THE UNIVERSITYOF ILLINOISLIBRARY370.E>^. l4-cop.v^2LIBHARYDigitized 'by the Internet Archivein 2011 with funding fromUniversity of Illinois Urbana-Champaignhttp://www.archive.org/details/studiesonnortham14millILLINOIS BIOLOGICALMONOGRAPHSVol. X] V . No.Published by the University of IllinoisUnder the Auspices of the Graduate SchoolUrbana, IllinoisEDITORIAL COMMITTEEJohn Theodore BuchholzFred Wilbur TannerCharles Zeleny1000—i-36—7536STUDIES ON NORTH AMERICANCERCARIAEWITH EIGHT PLATESByEdwin Lynn MillerContribution from the Zoological Laboratory of theUniversity of IllinoisNo. 475DistributedApril 28, 1936Ib (o oCONTENTSI. Introduction 7II. Methods of Investigation 9III. Discussion of Infection Records 11c' IV. Discussion and Key to the IlUnois Cercariae 23<:V. Cystocercous Cercariae of Liihe 26^ VI. Monostome Cercariae 36VII. Echinostome Cercariae 40VIII. Xiphidiocercariae 46IX. Furcocercous Cercariae 78X. Cercariaea 96XI. Summary 99Bibliography 100Plates 105Index 122ACKNOWLEDGMENTSTo Professor Henry B. Ward, under whose directionthe investigations have been carried out, the writer wishesto acknowledge indebtedness for the use of his valuableprivate library and for his suggestions and helpful criti-cisms. Also a number of friends and fellow students haveaided materially in the identification of mollusks and thecollection of material during the course of the followingstudies.I. INTRODUCTION*From the time of Joseph Leidy to comparatively recent years Ameri-can larval trematodes and trematode life histories have received increas-ing attention. Before Cort published his pioneer work on larval trema-todes of Illinois, very little was known about these larvae in NorthAmerica, and even in Europe only a few life cycles were known. Up to1914 only twelve cercariae had been reported from North America, butin the same year Cort added fourteen new species to this list.Faust described fifteen additional species in 1917 and two years latercompiled a list of eighty-one described forms from the United States.Such studies became more prevalent soon after this time, so that McCoyin 1928 estimated the number of described cercariae in this country asabout one hundred, but stated that the complete life histories of onlyfour trematodes in the United States were known. Up to 1929 ten com-plete life histories had been described.While these estimates may in some cases be incomplete, neverthelessthey serve to show one of the trends of modern investigation in the fieldof Helminthology. Now the number of described cercariae in this countryhas reached such proportions that it is not practical even to refer to allprevious descriptions in this paper. Descriptions from the state of Illinoisalone, including those in the present paper, cover thirty-eight species.In some attempts to establish life histories of these forms, eitherexperimentally or morphologically, many errors have occurred, largelybecause of vmsubstantiated generalizations or insufficient experimentation.Due to a diversity of structure within each of the several larval groups,I find many difficulties are encountered in determining a relationship be-tween the morphology and the developmental cycle. In short, I believeDollfus (1914) was right when he stated that cercariae very similar instructure dwell in different hosts and have very different kinds of de-velopment, and that cercariae very different morphologically live in iden-tical environments and have similar courses of development.In his classification of cercariae in 1909, Liihe recognized five majorgroups, Lophocercariae and Gasterostome, Monostome, Amphistome, andDistome Cercariae. He further subdivided the Distome Cercariae intothe Cystocercous, Rhopalocercous, Leptocercous, Trichocercous, Furco-cercous, Microcercous, and Gorgonocephalous Cercariae, as well as tail-less cercariae.*It is not convenient to consider here several publications which have apiieared since thismanuscript was completed in 1934.8 ILLINOIS BIOLOGICAL MONOGRAPHSLebour (1912) used the development in sporocysts or rediae of theseforms as a basic factor in her scheme of classification. Viewing thisplan now in the light of numerous additions to taxonomic lists of cer-cariae from various parts of the world, I realize that such a scheme candenote only very general relationships since individuals of the subgroupswithin each of these two large groups differ greatly in most other respects.No one can doubt that an accurate classification of cercariae basedpurely on relationship would be of great value in indicating possible cluesto the life histories of closely related larvae. However, the still inade-quate knowledge concerning the value of many larval characters in re-vealing adult relationships and the inadequate descriptions of manycercariae make such a classification still impossible for all of the de-scribed larvae.Certain larval structures, such as the number and position of the pene-tration glands, the shape of the bladder, the branching of the excretorysystem, the shape and size of the stylet, and the character of the germinalmass, should be regarded as less important for definite specific diagnosesand more important for showing subgroup relationships. Earlier workerswere sometimes inclined to regard these characters as specific.Perhaps the statement of Faust (1917) shows adequately the view-point taken by some more recent workers, when he says: "The writerhas attacked this part of the problem with the idea in mind that not onlythe fundamentals of the adult trematode are found in the mature cercaria,but that even the main descriptive features of the adult trematode arealready present, so that the worker can recognize the adult in the larva."After various studies on many cercariae I am inclined to depart some-what from the above viewpoint, for while many of the larval charactersresemble closely those of the adult, yet I find several incompletely de-veloped structures in the cercaria which bear little resemblance to thesame structures in the adult. For instance, the poorly defined and shape-less germinal mass of the emerged furcocercous cercaria bears Uttleresemblance to the reproductive organs of the adult trematode. Thecharacter of the excretory system may change due to the division of theflame cells and the growth of tubules and capillaries, and even a ventralsucker may appear during the metacercarial stage (McCoy, 1929). Il^elieve the above facts must be considered carefully if we are to progresstoward the use of dependable characters of the cercaria for specificdiagnosis.Similarity between excretory systems has proved to be of greatvalue in determining relationships but I find this similarity too great tohave the systematic significance given it by some workers. Several in-stances of difTerent species of cercariae, as well as different species ofNORTH AMERICAN CERCARIAE—MILLER 9adults, are on record in which the excretory systems are identical as to thearrangements of the tubules and terminal cells.The discovery that many cercariae do not have the host-specificityoriginally supposed has brought to light almost identical descriptions offorms from different molluscan hosts.The following studies may help in clarifying some of the earlier errorsin taxonomy and descriptions of North American cercariae, and will addto the information concerning the life histories of several forms. De-scriptions of four new cercariae are included in the morphological sectionof this paper, and I have added to the knowledge of nineteen additionalspecies.It is hoped that the survey of the Illinois forms and the summaryof the localities and hosts from which each form has been reported maybe of use to future investigators.II. METHODS OF INVESTIGATIONFormer workers who have placed emphasis on the study of livingforms have recognized the advantages in such methods. Earlier descrip-tions of cercariae based on preserved and mounted material are re-sponsible for much of the confusion existing in the literature at present.Such descriptions have made it impossible to determine the identity ofmany such forms with certainty and have made their inclusion in iden-tification keys and systems of classification highly problematical.As pointed out in my earlier paper (1930), technique methods do notinsure a similarity in the proportions of body structures before and afterkilling and fixing. Obviously the study of such material cannot give atrue and complete concept of these forms.For these reasons the great majority of my investigations have beenbased on living specimens, and detailed studies of all forms included herehave been made on the living animals with the aid of an oil immersion.Pressure of the cover slip is advantageous since it makes structures morevisible. It also slows down the activity of the worm so that more accuratemeasurements can be completed on the living form. Most of the follow-ing observations were made on living cercariae under uniform pressurewhich was just strong enough to prevent rapid movement.Measurements without explanations of the stages of contraction orexpansion of the body mean very little. Therefore I have tried particu-larly to obtain measurements at various stages of body contraction andextension. Only in this way can such measurements be of use to futureinvestigators. Abundant material for the study of local forms has made10 ILLINOIS BIOLOGICAL MONOGRAPHSthis possible. All measurements mentioned here, unless otherwise speci-fied, were made from living material, and represent the averages for atleast five different individuals.Recent workers have shown the error in basing descriptions ononly partially developed cercariae which have been secured by dissectionof the molluscan host. The following morphological studies have beenmade from cercariae after emergence from the mollusks. However,Stunkard (1930) has found that cercariae may leave the sporocyst orredia while still immature, and complete their development in the lymphspaces of the mollusk. My own observations have corroborated this, and,in addition, there is evidence that at least some of the stylet cercariae,under conditions of high temperature in small pools during the hot sum-mer months, emerge from the snail prematurely. In such cases there areseveral points of difference between their structure and that of formswhich emerge during the colder fall and spring days. It has been sug-gested in recent descriptions (Beaver, 1929; Horsfall, 1930) that someearlier descriptions have been based on such immature forms.It would seem that abnormal conditions as yet little understood are atwork, when observations show that at least with some species, thoseleaving the snail soon after it has been placed in a laboratory aquariumencyst normally, but those appearing later due to this artificial rise intemperature die without encysting. Perhaps their development has beenspeeded to such an extent that they break from the sporocyst and emergefrom the snail prematurely, death consequently resulting. This may alsoexplain why many hosts remain uninfected during the experimental lifehistory studies of cercariae.As indicated in the tables of collection records and in the collectiondates in the description of each species included in this paper, my workextended over the period from September, 1931, to July, 1933. In thelaboratory the snails were isolated in small vials or boittles and examinedrepeatedly for about forty-eight hours. Those not giving off cercariaewere later examined for infections so that the rediae or sporocysts anddeveloping cercariae might be studied. Infected individuals were segre-gated in small containers so that the movements of the emerging cercariaecould be studied before microscopical studies were made. Later, cystswere recovered for study from the inner walls of these containers andfrom the snails themselves since they often serve as the host of theencysted forms as well, particularly for the echinostome cercariae.Incidence of emergence could be studied too, and has been mentionedin the descriptions of some species. Parasitized snails frequently die inthe laboratory, although, in some cases, it has been possible to keepseverely parasitized hosts for long periods.NORTH AMERICAN CERCARIAE—MILLER 11Cercariae were fixed with warm Gilson's fluid, saturated corrosivesublimate fixing fluid, and corrosive acetic. Sections of the liver, includ-ing sporocysts or rediae, were also fixed and in all cases preserved in 75%alcohol. Entire mounts of the cercariae, sporocysts, and rediae were madefor additional study and later reference, after staining with Delafield'shematoxylin, Ehrlich's acid hematoxylin, Mayer's paracarmine, alumcochineal, and Mallory's phospho-tungstic hematoxylin.In addition to the methods mentioned above, intra-vitam staining wasused in these studies. The use of neutral red for staining certain glandsand organs in the living animal proved to be very valuable, particu-larly for distinguishing the number of penetration glands and the slender,undeveloped ceca of the digestive system, both important points in iden-tification. Weak solutions of methylene blue, introduced under the cover-slip, aided in locating spines of the tail and body, and the collar spines ofechinostome cercariae.II T. DISCUSSION OF INFECTION RECORDSAn examination of the data on moUuscan infection with the cercariaediscussed in this survey brings out a number of interesting features ofthe work. As previously mentioned, the reporting of many molluscanhosts for the same species of cercaria in the same locality has beenquestioned. However, Cort (1918) gave several striking examples ofthe lack of specificity in the choice of intermediate hosts, notably thehuman schistosome cercariae, C. douthitti Cort 1914 and C. douglasiCort 1917. He submitted data to support this contention and said: "Thedata given above seems to clearly indicate that the forked-tailed cercariaereadily adapt themselves to new molluscan intermediate hosts."Many species have now been reported from a wide variety of hosts.From my own records I can say with certainty that C. acanthocoela hasbeen found in Physa gyrina hildrethiana and Helisoma trivolvis; thatC. mesotyphla occurs in Physa gyrina hildrethiana, P. halei, and P.gyrina; that C. pteractinota infests both P. gyrina and H. trivolvis; andthat C. trivolvis Cort 1914 was found in both H. trivolvis and P. gyrina.In fact the very existence of many forms depends upon their cosmo-politan adjustment to various hosts in different localities. This has beenproved by distributional and experimental studies.Miller and Northup (1926) concluded that there is a semi-annualrise and fall in the larval trematode infestation of Nassa obsoleta. Theybelieved this was due to the migration of the definitive hosts and thedegree of their infestation, as well as the life span of Nassa and the12 ILLINOIS BIOLOGICAL MONOGRAPHSeffect of parasitism upon it. While my collections were not regularenough to base such conclusions on them, there is some evidence inTable I to show the effect of the long severe summer drouth of 1931 onthe larval trematode fauna of gastropods. The instability of this faunain a particular body of water is also apparent. No doubt many of theholostome cercariae, as well as others, reach local bodies of water throughthe infected excrement of migrant or summer-resident birds. A certainspecies of cercaria may be found only once in a given locality, eventhough collections are continued over a period of several years. But eventhough many of the species studied are isolated in particular bodies ofwater, several forms, such as C. pteractinota, C. trivolvis, and C. meso-typhla appear to be distributed generally over the area represented by thecollections (see Table II).The data oft'ered by former workers to show the percentage of infec-tion which they found for larval trematodes were a compilation showingthe total number of infected snails, that is, both those with undevelopedcercariae and those with emerging cercariae. My data represent an at-tempt to determine the periods when emergence is normally at its height.Therefore, infections showing only completely developed cercariae areincluded in the following tables and are represented in the computationsof Table IV.Cort (1922) gave some idea of the enormous number of cercariaethat may emerge from a single snail host. He also showed the definiterelation between the number of sporocysts present in the snail and itsoutput of cercariae. Temperature has been shown by various workers tobe an important regulator of the emergence of cercariae from theirhosts. Studies of infected snails after they have been kept in the labo-ratory for a long period without feeding, indicate that the number ofescaping cercariae is greatly reduced by starving the host. In these casesthe sporocysts have always contained relatively few cercariae, and inmany cases I have noticed dead cercariae and disintegrating germ ballswithin the cavity of the sporocyst or redia.An examination of Table IV shows that Cercaria meniscadenais the commonest form found in the Urbana area, since over 10% of thePleurocera acuta collected were infected with emerging cercariae. In all,emerging cercariae from about one hundred snails were studied. Theseinfected snails represent about 2.98% of the total number collected fromall localities. A few snails were collected at Baton Rouge, Louisiana,Sinking Creek and St. Charles, Alissouri, and Leesburg, Florida. Theselocalities have been clearly indicated in Tables I and II. All other col-lections were made in Illinois, chiefly in the vicinity of the University ofIllinois at Urbana.NORTH AMERICAN CERCARIAE—MILLER 13l-O l-O->l1 'Of^ ro t-Oo O^U (U 1—1« oS 1- Q 1^M_i w rt c> :=;o f. O* •-^ f;^ "^3 ?5Species>cariaedeinthisCi.<5 § ^ r ^5UG G G;--d(U OJ-^ t1S ai o o o o .—(o o O O O ro r-H3 •+H CM^^^ y._2 "si c\ po o o r^ oo \0 1^ IT) o r^ vO u-)rO ro ro ^ o eg (VI r^ CMl-Ho^5o01c Co §_Cs^Q1-, s^^ Ji .c S .3 CoU 5 "55.^ ct 2"^2X t5 ' «^^ 2 g Qo-G tm'S V"?c 'S cC« .5t".^ ?». V ?-i 's ?^ ?^. - <^ "0 ^£ £<3)s-!-i.cCI.u 4.E Ea.Ec c cj; Ert> ^cCOI-^'^ o n n y -*- ^- a. 0. c rt(U oo:1-'oc1,Eco:2a:>cc>cPh(L)a:rtc>KC5c oT&•^ngam ngamk* y c a 0: re re >C C o IIL cr U ir XT H4}rtQ^ ^ ,_ ,_^ _ ^c^ c<- ro t^ r'' r'' r<- r<~ ro,_4 rv^^ vC C OJ u-^ COrg CN a- O O 0- O-14 ILLINOIS BIOLOGICAL MONOGRAPHSO<* 'fljuUO ^—• oj .cy rt -^a,CO rt'o3 t:^3(U O^^(InQC o• ~ CM-4CN .5 1-^Uu U< •3 U « u •^ ; J 12 -1- • S •- !, -^ =^ ~^ ^^ 'u c^~ 5 "r' '"' r> ^*^ ^ T—4« ."i; --I ?^J ? Jw s w ^w5^^wu U o G G'-I O CM T-H O O O >—*>—'00 "—I '—I t—I^IS) *-JS rtu C-o^uco DCLhOw ^o XU (JC5 iSl ~cl; a,' s:'SiDPh Ut/) 1-1<1J^ oJ CL^c -H U QUuNORTH AMERICAN CERCARIAE—MILLER 15H ii m.f-* 1j 5hJ ^ J JXL) ^ W S'§ <3 W s w" ^wL G u Ij G G uV- -0 CM (\ C? 00 CM•r-* C^" t^ rn f CM^I^ 3"t: (N r—i in<-HcnC^u Vs ac nCrt Docrt;^ -o E r^ ri| C cr ^ X.^ :h1-0,a-t^ (L) crs _> C/1>u _>a;(L.fo c5 s1—>'~7'L;_ bfi c CO c^fin U ^ U B ^' sT1 Srtboc1.rtX Xrt OJ ct rt rt r: rtU J c/- u CO ^9JrtQr—i ,-^ ,_tr^ ror^ ro --^ro<~ot^ CO C OC -t'(V•^ (J 1) flj tA r *—•*j (U > en IT ^ C02 ZZV O s ^- rt ^U c^J^^ 5 ^a.'i 20,a.c/T 1beP^ E U tr ^ c be 2 > c03 03"a.c'0CO U < u CO C 0-njrtQr^ CV] (M (N r^^^, ^ -r) V >n r- oCGrtUCa (u ru OJ ^ Ji^S 2 ^?J §.Ki•SlI ^s w ^ w -. wu L) u^ o o o o^H-1bo3OPicoCO 00 Ma: ^' ci,'ma3 feT—1(U«=^ ^-s (t!H hJ«"S5a o =; '^li.<3i ^PbOoco18 ILLINOIS BIOLOGICAL MONOGRAPHSL)QH^ ^u1 LO U-) lO 1^ IT)ro •^ s? rO CO. -o O Oj On O o\U C CI-»—--2 ^5 *--2 J:iSpeciesofcariaedescinthispa 0013 5 c^ IStrivolvisCort1914hamataMiller192^pteractinoE.L.Mill1^t-5-u5c3au u G u G "J DUGu-CIL> OJ-^ r;C (- m • 5 p • H "?Id?^ v ?*,^.c; C31 C31^Cj> ~1!eJ cC CIh' :i: i: CiJ^'> o O1) o s 1—. jf 1—>iJ u ^ ^ be ^OS ^^^ 5 en 3 COE OCO£rtboCmoOoo«rtQoj rvi (n" CMro rO ro ro: c^ « -" ^ Sp lU o ^ 2 oj -- ;G u G G G^ur-H CM55>^u^ T)'^(1)rtis.8. C. zvardi Miller 1923 ; from Urbana and St. Joseph ; in H. trivolvis.9. C. pteractinota E. L. Miller 1935; from Paris; in P. gyrina.Xiphidiocercariae1. C. heinilopJiura Cort 1914; from Rockford; in P. gyrina.2. C. isocotylea Cort 1914; from Urbana and DeKalb; in H. trivolis.3. C. polyadena Cort 1914; from Chicago; in Lymnaea reflexa.4. C. stilifera Faust 1918; from Mt. Morris; in P. gyrina.5. C. trifurcata Faust 1919; from Urbana; in P. gyrina.6. C. candelabra Faust 1919 ; from Urbana ; in H. trivolvis.7. C. mesotyphla E. L. Aliller 1935 ; from Muncie, Seymour, Sadorus, Alhambra,St. Joseph, and Rantoul ; in P. gyrina, P. gyrina hildrethiana, and P. Iialci.8. C. cystorhysa E. L. Miller 1935; from Homer; in Goniobasis livescens.9. C. meniscadena E. L. Miller 1935 ; from Mahomet ; in Plenrocera acuta.10. C. acanthocoela E. L. Aliller 1935; from Urbana, St. Joseph, and Seymour; inH . trivolvis and P. gyrina hildrethiana.11. C. steganocoela E. L. Miller 1935; from Seymour, Sadorus, and Urbana; in P.gyrina hildrethiana.12. C. pachycystata E. L. Miller 1935; from Seymour and Henry; in H. trivolvis.The above forms have been arranged in the form of a key for con-venience in identification.NORTH AMERICAN CERCARIAE—MILLER 25Key to the Illmois Cercariae(71) Cercariae with tail which is not forked 2Only one sucker and that at anterior end—Monostome Cercariae 3Only two pigmented eye-spots—BinoculateCercariae C. aurita Faust 1918.Three pigmented eye-spots—Trioculate Cercariae 5Body spines present C. spatula Faust 1919.Body spines not present 7Excretory system consisting of only a bladder and two large collect-ing tubules filled with granules C. urhanensis Cort 1914.Excretory system with accessory capillaries and flame cells 9Caudal excretory tubule unbranched, except at terminal fork ; bladderU-shaped C. infracaudata Horsfall 1930.Caudal excretory tubule with many branches ; bladderspherical C. robusta Faust 1919.Body possesses two suckers 12Second sucker ventral and at posterior end of body—AmphistomeCercariae 13Body unpigmented except for narrow area aroundeyes C. diastropha Cort 1914.Anterior one-third to one-half of body heavilypigmented Cercaria of Allassostoma parvuin Cort 1914.Second sucker ventral but not at posterior end of body 16Body possesses long heavy tail not used in swimming 17Tail has invaginated distal end ; not swollen at base—Gymnocephal-ous Cercariae C. megalura Cort 1914.With heavy tail swollen at proximal end, into which the body may bewithdrawn—Gorgoderine Cercariae 19Distal portion of tail long and fiHform; nostylet C. sphaerocerca E. L. Miller 1935.Distal portion of tail not filiform; styletpresent C. mitocerca E. L. Miller 1935.Tail slender and used in swimming 22Stylet present 23Tail with fin-fold—Cercariae Ornatae 24(26) Excretory bladder club-shaped C. hemilophura Cort 1914.(26) Excretory bladder small, crenate, with anterior end prolongedinto two lateral collecting tubules C. trifurcata Faust 1919.(25) Excretory bladder with two vesicles separated by a very narrowconstriction C. mesotyphla E. L. Miller 1935.Tail without fin-fold 28One or two penetration glands on each side—Cercariae Microcotylae. . . .29With characteristically wrinkled, rectangularbladder C. cystorhysa E. L. Miller 1935.With U-shaped bladder C. vieiiiscadena E. L. Miller 1935.More than two penetration glands on each side—Cercariae Armatae 32Elongated bladder consisting essentially of a posterior vesicle and twolateral ones 33Many bluish, oil-like droplets throughout body; four penetrationglands on each side C. pachycystata E. L. Miller 1935.Body without oil-like droplets 35No trace of digestive ceca posterior to pharynx 36Six to eight penetration glands on each side...C. isocotylea Cort 1915.Ten to twelve penetration glands on each side.C polyadena Cort 1914.With complete digestive tract, including ceca 39(41) Twelve penetration glands on each side...C slUifcra Faust 1918.26 ILLINOIS BIOLOGICAL MONOGRAPHS40 (39) (41) Nine penetration glands on eachside C. steganocoela E. L. Miller 1935.41 (39) 40) Seven to eight penetration glands on eachside C. acanthocoela E. L. Miller 1935.42 (32) Bladder composed of anterior and posterior vesicle with mediumconstriction C. candelabra Faust 1919.43 (22) Stylet absent ; collar spines developed or absent—EchinostomeCercariae 4444 (49) Swollen excretory crura filled with crystals 4545 (46) Tail with fin-fold C. trivolvis Cort 1914.46 (45) Tail without fin-fold 4747 (48) Collar of 40 spines C. chisoleiiata Faust 1918.48 (47) Collar of 38 spines C. complexa Faust 1919.49 (44) Excretory crura without crystals 5050 (51 ) Tail with fin- fold ; no collar spines C. reflexae Cort 1914.51 (50) Tail without fin-fold; collar spines present. .C. afanZ/jo.s'iojna Faust 1918.52 (1) (71) Cercariae with forked tail 5353 (54) Large basal tail stem into which body can be withdrawn—CystocercousCercariae C. niacrostoina Faust 1918.54 (53) Body cannot be withdrawn into tail stem—Furcocercous Cercariae 5555 (60) With no ventral sucker 5656 (57) With two small pigmented eye-spots C. multiccllulata Miller 1923.57 (56) Without eye-spots 5858 (59) Oral sucker pyriform C. rhahdocaeca Faust 1919.59 (58) Oral sucker oval in shape C. haniata Miller 1923.60 (55) With ventral sucker 6161 (62) Without eye-spots C. rohusticauda Faust 1919.62 (61) With two pigmented eye-spots 6363 (64) Furcae longer than one-half the stem length.... C. minima Faust 1918.64 (63) Furcae shorter than one-half the stem length 6565 (66) A posterior mucin gland present C. ti'ardi Miller 1923.66 (65) No posterior mucin gland present 6767 (68) Four penetration glands on each side of body. . .C. douthitti Cort 1914.68 (67) A great many penetration glands filling the entire region posteriorto the eye-spots 6969 (70) Furcal fin-folds closely fluted; without furcalrays C. gigas Faust 1918.70 (69) Furcal fin-folds braced with radial furcalrays C. pteractiiiota E. L. Miller 1935.71 (1) (52) Tailless larvae—Cercariaea Leucochloridium problematicuin Magath 1920.V. CYSTOCERCOUS CERCARIAE OF LUHEFor many years tlie term Cystocercous was used to designate a mis-cellaneous group of cercariae, each of which is able to draw its bodywithin the tail appendage where it encysts or remains unencysted. Theearliest form to be described for this group is Cercaria macrocerca Filippi1854. All subsequently added members of the group also possessed verylarge tails and the name Macrocercous was naturally applied to suchmembers. It was found some years ago when their life histories beganto be worked out that this grouping was very artificial, and at presentthree distinct groups should be recognized. Various workers haveNORTH AMERICAN CRRCARIAE—MILLER 27spoken of them as the Cystophorous Cercariae, the CystocercousCercariae, and the Macrocercous or Gorgoderine Cercariae. I shall con-sider them in the above order.Cystopttorous CercariaeHistory and DefinitionWagener described the first cj^stophorous cercaria to be reported in1866, and called it Cercaria cystophora. He found it in Planorbismarginatus. Sonsino (1892) described C. capsidaris from Cleopatrabulmoides and later Looss (1896) said that it belonged to this group.Pelseneer (1906) reported two marine species of the group, namely C.appendiculata from Natica alderi and C. vaidlegeardii from Trochnscinerariiis.When Liihe (1909) listed C. cystophora in his key to the CystocercousCercariae he said about it: "In die Kanimer ist ausser dem Korper desspateren Distomums auch das seitlich abgeknickte Schwanzende Zuriick-ziehbar. Entwicklung in Redien in Planorbis."Sinitsin (1911) defined the group of Cystophorous Cercariae as:"Cercariae which are characterized by possessing a vesicular tail withvarious appendages upon it." He also added two new marine species.Cort and Nichols (1920) gave a more detailed discussion of theCystophorous Cercariae when they added a new species, C. californien sis,to the group. They assigned the following characteristics to the group:1. All cystophorous cercariae except C. vaultegeardii develop in rediae.2. Mother sporocysts where rediae develop have been described for C. Sagittariusand C. cystophora, but none have been found where rediae contain rediae.3. All species lack larval structures for penetration and encystment ; stylet, cysto-genons, and cephalic glands absent.4. Each species has a tail with a central vesicle into which the body can be with-drawn.Sewell (1922) refers four previously described cystophorous cercariaeto his Appendiculata group, along with a new species, Cercaria indicaeXXXV. His definition of the group can apply to all cystophorous cercariaebut he does not explain why he has included only five of the ten formsknown at that time in his new group. His definition follows:(1) The distome body is somewhat elongate in shape and is colorless and trans-parent ; the two suckers are of equal size.(2) The mouth leads back to a pharynx which is followed by a triclad gut.(3) The excretory bladder is elongate, reaching forward nearly to the acetabularmargin.(4) The tail is complex and consists of two parts, a distal, flattened or cylindricalprocess, and a proximal, rounded or oval, and much swollen portion thatforms a cyst containing a long slender filament.(5) Development occurs usually in rediae which in turn arise from sporocysts.The redia has a well-marked pharynx and gut, but is devoid of loccjmotorprocesses.28 ILLINOIS BIOLOGICAL MONOGRAPHSC. vaullegeardii and C. capsularis differ from the other members ofSewell's Appendiculata group in that they develop in sporocysts insteadof in rediae as do the other species.The following cystophorous cercariae have been described:1. Cercaria cystophora Wagener 1866 9. C. syringicanda Faust 19222. C. capsularis Sonsino 1892 10. C. indicae xxxv Sewell 19223. C. appendiculata Pelseneer 1906 11. C. calliostomae Dollfus 19234. C. vaullegeardii Pelseneer 1906 12. C. invaginata Faust 19245. C. Sagittarius Sinitsin 1911 13. C. macrocercoides Faust 1926 (C6. C. laqueator Sinitsin 1911 macrura Faust 1921 preoccupied)7. C. yoshidae Yoshida 1917 14. C. biflagellata Faust 19268. C. californiensis Cort & Nichols 1920 15. C. projecta Willey 1930Cystocercous CercariaeHistory and DefinitionBraun (1891) first described and named one of these anchor-tailedcercariae and gave it the name of Cercaria mirabilis. Faust (1918c)added two new species, and described the group as follows:Aside from their anchor tail the species of this group possess other charactersin common which demonstrate their close relationship. Among these are thecrowded ceca with granular contents, the long median Y-shaped excretory bladder,the presence of the ovary and pair of testes close behind the acetabulum, and theswollen cirrus pouch anterior to the acetabulum. ... In general, the cercariaedevelop as the parthenogenetic offspring of sporocysts. They are found in therespiratory or digestive organs of snails.Sewell (1922) listed six of the eight forms belonging to this groupthat had been described up to that time in his new Mirabilis group. ThisMirabilis group, which included only these six cercariae, he described asfollows:(1) Development probably occurs in sporocysts; but the parthenitae have onlybeen recorded in three forms.(2) The tail is extremely large and wide, and at its anterior end forms a cavityinto which the distome may be partially or completely withdrawn, exceptin the case of C. fusca, in which it is connected to the body by a shortfold.(3) A pair of suckers are present.(4) A well-developed pharynx appears to be present, and the alimentary canalconsists of a very short oesophagus which almost at once divides into longwide intestinal caeca reaching back to the posterior end.(5) The excretory vesicle is elongate and is continued forwards as a median tubeto the acetabular region, where it divides into two lateral branches.The list of described cystocercous forms consists of the following:1. Cercaria mirabilis Braun 1891 7. C. pckinensis Faust 19212. C. wrighti Ward 1916 8. C. stephanocatida Faust 19213. C. anchoroides Ward 1916 9. C. splendens Szidat 19324. C. macrostoma Faust 1918 10. C. melanophora Smith 19325. C. hrookoveri Faust 1918 11. C. hodgesiana Smith 19326. C. fusca Pratt 1919NORTH AMERICAN CERCARIAE—MILLER 29GORGODERINE CeRCARIAEHistory and DefinitionThe first cercaria described which belongs in this group is Cercariamacrocerca Fihppi 1855. Later Wagener (1857) and Thiry (1860) re-ported this species, but Sinitsin (1905) demonstrated that their reportsrepresented distinct species. Others worked on the life cycles of theseforms, but much of the work was not experimentally conclusive.Luhe (1909) and Sinitsin (1905) agree in calling the C. macrocercaof Thiry (1860) a new species. Sinitsin described it (1905) and namedit Cercaria gorgoderae pagenstecheri. Sinitsin also demonstrated thatthe C. macrocerca of Wagener was a distinct species and named it Cer-caria gorgoderae loossi. In 1905 Sinitsin described Cercaria gorgoderaevarsoviensis. The life history discussions which Sinitsin submitted lackexperimental evidence.Kowalewski (1904) described Cercaria gorgoderae cygnoidis andLiihe agrees that this is the larva of Gorgodera cygnoides.The following list includes all gorgoderine cercariae that have beendescribed up to the present time.1. Cercaria macrocerca Filippi 18542. Cercaria gorgoderae cygnoidis Kowalewski 19043. Cercaria gorgoderae loossi Sinitsin 19054. Cercaria gorgoderae pagenstecheri Sinitsin 19055. Cercaria gorgoderae varsoviensis Sinitsin 19056. Cercaria sphaerocerca E. L. Miller 19357. Cercaria mitocerca E. L. Miller 1935When Liihe (1909) separated these forms from the cystocercouscercariae he described them as follows: "Schwanz ziemlich drehrundund nicht gabelig. Bohrstachel vorhanden. Sporocysten in Sphaerium.(Macrocerke Cercarien von Gorgoderien)."Sewell divided this group into two divisions according to the relationof the individuals to the adult genera Gorgodera and Gorgoderina, butsince experimental evidence for such a classification is lacking, I amomitting this subdivision.During my study of cercariae of the Urbana region, I examinedspecimens of Muscidiitm transversa, taken from the Salt Fork Oxbowjust north of St. Joseph, Illinois, on November 24, 1931, and again onFebruary 20, 1932, and found them to be infected with a gorgoderinecercaria. The individuals were found within the gill tissue of theMusculium, lying between the gill filaments. After considerable study Ifound it to be a new species of cercaria which very likely is a larva ofone of the Gorijoderinae.30 ILLINOIS BIOLOGICAL MONOGRAPHSCercaria sphaerocerca E. L. Miller 1935(Figs. 1-9)The distorted appearance of the body and the awkward shape andgreat size of the tail give to this cercaria a most unusual appearancewhich is quite distinctive from all other cercariae which I have eitherstudied or noted. The tail is noticeably divided into two distinct regions,a narrow posterior region, greatly elongated, and a swollen or inflatedanterior region resembling that of the other gorgoderine cercariae, andseveral times larger than the body of this cercaria (Fig. 4). At theproximal end of the tail is a bell- or funnel-shaped structure with thick-ened sides and a central core which serves as an attachment for the bodyof the cercaria. Just distal to this structure is a constricted, neck-likeportion which separates the bell-shaped cyst cavity from the large tailglobe. The body is elongate and narrow (Fig. 1), pointed at the posteriorend when well extended, and rounded when contracted. The anterior endof the body is narrow but broadly rounded.The body of this cercaria breaks loose from its tail easily and will dothis readily when the cover-slip is pressed, or even because of its ownmovements in the tap water. I find that the cercariae have broken loosefrom their tails and are encysted inside the sporocysts after the deadtissues of the Musculium have been kept in tap water for about twenty-eight hours. However, they were found also encysted within the cystcavity or expanded chamber at the proximal end of the tail (Fig. 3),which is quite probably their normal method of procedure. They twistabout freely inside the cyst wall, this wall being thin, transparent, pliableand tough, so that it can be pushed out of its normal shape easily. Anumber of cysts were found in the containers but whether they w^erecysts of cercariae which had escaped from broken sporocysts, or wereformed by cercariae which escaped normally from the sporocysts, is apoint which was not determined.Annular wrinkles extend around the body. Upon examination underhigh power these wrinkles appear to be horizontal rows of tiny swollenareas which are papillae. These papillae are less distinct on preservedcercariae. Projections are also located on the dorsal lip of the oralsucker. The body is an elongate oval in outline and the ventral sucker isa little posterior to the middle of the body. The posterior portion ofthe body proper is flattened and appears almost fan-shaped at times.A small stylet is present, dorsal to the cavity of the oral sucker, butit is somewhat different from that described by earlier workers for othermembers of this group, as it lacks the lateral points along a ventral sharpblade as well as other structures so well illustrated by Sinitsin (1905),NORTH AMERICAN CERCARIAE—MILLER 31and Liihe (1909) (Fig. 6). It is connected posteriorly by a group offrom six to eight stylet glands on either side of the body just anteriorto the acetabulum. These glands connect to a main duct which isbipartite at least in the anterior part of its course.In the region of the body, posterior to the acetabulum and along eitherside of the elongated excretory bladder, is located a number of elongateglands in a rather regular group like those pictured for Cercariagorgoderae pagenstccheri by Sinitsin (1905), but not in as regular a for-mation as those of Cercaria gorgoderae loossi. When, however, thebladder becomes deflated the regular character of these cells is more likelyto be obscured.The acetabulum is larger than the oral sucker and is posterior to themiddle of the body, varying in position from a point just posterior tothe center, to the anterior edge of the posterior one-third of the body,depending on the state of contraction since the posterior region of thebody in particular is capable of contracting to an astonishing extent. Inside view this sucker appears as a cup-shaped structure, attached by itsbase only to the body of the worm (Fig. 5). No pharynx or prepharynxis present; the esophagus extends posteriorly to a point about two-thirdsof the distance from the oral sucker to the acetabulum, before it dividesto form the intestinal crura. These crura reach a point slightly posteriorto the halfway mark between the acetabulum and the posterior end ofthe body.The excretory bladder is a long expulsion canal in this form, reach-ing from the posterior dorsal excretory pore to a point a short distanceposterior to the acetabulum. In side view this bladder is a typical club-shaped structure with its enlarged end forward. Its shape is constantlychanging but usually both an anterior and a posterior bulb are evident(Fig. 8). Two main collecting tubules divide into two branches justposterior to the anterior limits of their courses. The anterior branchredivides just posterior to the oral sucker. The posterior branch ex-tends posteriad to a point slightly behind the acetabulum where it dividesinto two branches, the posterior one of which redivides immediatelylateral to the excretory bladder. Finer branches and flame cells arepresent but their exact location has not been determined.The following measurements were made while the living worm wassubjected to rather strong pressure of the cover-slip, and during a stateof contraction, in most cases. When the body is only partially extendedit measures 0.576 mm. in length and 0.144 mm. at its greatest width,which is through the region of the acetabulum. The suckers were alsomeasured when the worm was slightly extended and subjected to strong32 ILLINOIS BIOLOGICAL MONOGRAPHSpressure. The oral sucker is 85 ;li long and 78 ^i wide, while the ace-tabulum is 0.104 mm. in longitudinal diameter and 0.111 mm. in trans-verse diameter.In measuring the tail greater pressure was necessary. The constrictedregion is 0.616 mm. long and the swollen portion, or globe, is only 0.392mm. in length by 0.252 mm. in width. Because the greatest width wastaken, it was necessary to measure the area just posterior to the centerof the swollen part. The bell-like structure in which the cercaria wasoften found encysted, was measured after the cercaria had brokenloose. It is 56 jx in length and 84 /i in width when it is contracted. Thetotal length of the entire cercaria is about 1.64 mm.The large tail is sluggish in its movements but after becoming de-tached in the water of the container sometimes remains active longer thanthe body. No definite bodies are discernible in this globe but it is com-posed of large, clear, irregular-shaped divisions (Fig. 2), which areeasily seen when the worm is observed under high power of the micro-scope. These are similar to the divisions described by Sinitsin (1905) forC. gorgoderae varsoviensis. Rounded nuclear bodies are also locatedthroughout this globe. Smaller angular bodies as well as larger roundedbodies are present but the triangular ones are more common in theposterior portion of the globe (Fig. 7).In the region between the swollen and constricted portion of the tail,is a small group of tiny glands, which has also been noted in other close-ly related forms. There are smaller groups in other portions of the tail,with the exception of the central core. The narrow part of the tail,when at rest, possesses peculiar lateral folds which are always locatedin the same regions of the tail, two groups being on either side of thetail at the base of the constricted portion and two similar groups nearthe anterior edge of the posterior one-third of this part. It is possiblethat the muscle fibers of these regions function to produce the swaying,back-and-forth movement, mentioned by Luhe (1909) for similar forms.This cercaria matures in an elongated irregular sac-like sporocystwhich tapers at the end where it is attached to the gill tissue of thehost and where there is a prominent knob projecting from the body,although this structure is not always present (Fig. 9). Only briefmention has been given to the sporocyst in descriptions of the fewknown closely related cercariae. Perhaps one reason for this is that theend opposite the knobbed end is filled with pigment which makes observa-tion difficult. In fact the older sporocysts are not transparent enoughto enable one to see the cercariae within, without rupturing the wall ofthe sporocyst. The young sporocyst extends and contracts in a sluggishmanner, but is still as active as some of the cercariae. It is more trans-parent than those more advanced in age and the germ balls can be seen inNORTH AMERICAN CERCARIAE—MILLER 33movement quite easily, as they are pushed from side to side during themovements of the sporocyst. The body wall is composed of unusuallylarge cells and becomes thickened at each end of the sporocyst.When the sporocyst is pressed the cercariae come out of it, and thebody of the cercaria, which has been folded at the side of the swollenportion of the tail, when it was in the sporocyst, straightens. Many ofthe sporocysts contain only one cercaria; perhaps the long period of con-finement of the host in the laboratory may have brought about this con-dition. This again, as has been formerly intimated, might indicate thatinfection of the molluscan host terminates of its own accord.Encysted forms were found inside the bell of the tail of individualsin the container. When subjected to pressure of the cover-slip theencysted individual was forced through the opening at the tip of thebell. These recently encysted individuals conform with the descriptionof the cercariae, in their appearance and measurements. Some cercariaehave also been found broken loose from their tails and encysted inside thesporocysts that had been freed from the gills of the Musculium and leftin water over night. Twenty-eight hours after encystment they were stillactive.Cercaria mitocerca E. L. Miller 1935(Figs. 10-15)The material which furnished the basis for this study was taken fromthe liver tissue of Actitionaias carinata collected in the Sangamon Rivernear Mahomet, Illinois, on Nov. 4, 1932. Very few cercariae from theUnionidae have been reported in North America. This is particularlystriking when one considers the abundance of these mollusks in almostall parts of the United States. Altogether about twenty species of theseAcephala from various parts of the world have been listed as harboringlarval trematodes. From North America, Leidy (1858) reportedCercaria diiplicata (Von Baer 1827), a rhopalocercous cercaria, and gaveas its hosts Anodonta fiuviatilis and A. lacustris.This cercaria resembles the other gorgoderine cercariae very much,but differs in that it has no stylet. There is no other cercarial groupwhose members resemble more closely this species, and since it is verysimilar to these species with the exception which I have noted above, Iam including it here.This cercaria resembles C. spliaerocerca, in that it possesses a longtail greatly swollen into a large body at its proximal end, and a narrowdistal portion. This posterior portion is very narrow and elongated, be-ing almost threadlike in its appearance (Fig. 12).The body is large, and elongated when extended, but when mediumh'contracted the posterior end appears as a wide Hare (Fig. 11) extending34 ILLINOIS BIOLOGICAL MONOGRAPHSlaterally from the sides of the body just posterior to the acetabulum,and much more compressed dorso-ventrally than the rest of the body.The edges of this portion of the body, when the worm contracts, re-semble the lobate edge of a contracted turbellarian. The posterior endis quadrate with a constriction in the region of the excretory pore.Lateral constrictions occur on either side of the body just anterior to theventral sucker (Fig. 10). This feature is evident in nearly all of thecercariae described by Sinitsin (1905) belonging to this group. Thesurface of the body is broken by several rather prominent papillae whichare more common on the anterior end. They extend posteriad along thesides to slightly beyond the posterior limits of the oral sucker.The size of the body varies greatly according to the state of contrac-tion. When well extended it often is 1.12 mm. in length and 0.269 mm.in greatest width, which in this form is in the region just posterior to theacetabulum, due to the lateral flare already mentioned. When contractedthe body is only 0.728 mm. by 0.448 mm., and when only mediumly ex-tended it is 0.952 mm. by 0.336 mm. The portion immediately posteriorto the acetabulum often flares outward, out of all proportion to the restof the body, measuring sometimes as much as 0.504 mm. in width.The oral sucker is terminal and the mouth opening is ventral. Fromside view the acetabulum is seen projecting ventrally. The oral sucker isslightly longer than it is wide; it is 0.14 mm. by 0.129 mm. when theworm is only slightly contracted. The acetabulum is located near themiddle of the body ; it is smaller than the oral sucker and is spherical,being about 0.126 mm. in diameter. It is located about 0.28 mm. posteriorto the oral sucker and 0.504 mm. from the posterior end of the body.The oral sucker opens into an esophagus, no pharynx being present,and extends for approximately one-half the distance from the oral suckerto the acetabulum before dividing to form the two intestinal crura, whichare relatively large and which extend to within 0.13 mm. of the posteriorend of the body. However, this distance varies greatly with extensionand contraction. The esophagus is about 0.104 mm. in length.No stylet is present, but ducts can be seen running posteriorly fromthe sides of the oral sucker in a lateral position. The location andnumber of glands could not be determined in this form, due to thepresence of many small cells in this region of the body.Extending from the posterior end of the body to within a short dis-tance of the acetabulum is the elongated excretory bladder or expulsioncanal. When contracted the sides are irregular and the posterior endis swollen into a slight bulb. This bladder and the main collecting tubulesresemble greatly those of C. sphaerocerca. It divides anteriorly to formthe two main collecting tubules which, in the anterior region of theNORTH AMERICAN CERCARIAE—MILLER 35body, turn posteriorly and run the entire length of the body again. Theybecome indistinct in the maze of tubules, large and small, which ramifythe body in all directions. Large flame cells are present in the body.A mass of large spherical bodies fills the major part of the bodyposterior to the acetabulum, and when the body is well extended theyseem to occupy a definite position and to resemble glands. They arecircular but are not S3'stematicall3^ arranged, as has been noted in otherspecies (Fig. 11). Also in this area are located three bodies, two ofwhich are lobed, and one unlobed, which I believe to be the reproductiveglands. Since the left posterior one is five-lobed and the right anterioris four-lobed, I believe these bodies will give rise to the two testes, oneof five parts and the other of four parts, in the adult. For this reasonI believe the form may be the larval stage of an adult gorgoderine bladderliuke. The ovary is anterior to the left testis and immediately posteriorto the acetabulum.Like C. sphaerocerca this cercaria contains a long, tail-like structure,consisting of an anterior swollen area and a posterior constricted thread-like portion (Fig. 12). The thread contains a hollow core throughoutits length, and there are scattered nuclei in both the globe and thread ofthe tail. The surface of the globe is covered with tiny fissures (Fig. 14),which have no definite arrangement but which connect and diverge in allpossible directions.At the proximal end of the globe is a spherical hollow structure havingthickened walls (Fig. 13). The body is attached here, and, when itbreaks loose, the opening snaps shut giving the appearance of a closedsphere. The globe measures about 0.448 mm. in length by 0.185 mm. inwidth, while the narrow portion has the great length of 2.128 mm. and awidth near its base of only 22 p.. The width tapers only slightly towardthe distal end of this thread.The sporocysts which give rise to these cercariae are ovate, broadly-rounded sacs, some with contracted tips at the smaller end of the sac(Fig. 15). No independent movement was noted in these forms, evenin the younger ones, but the cercariae could be seen within, moving aboutsluggishly. An average of the measurements of ten taken at randomgives a length of 0.980 mm. and a width of 0.462 mm.A few encysted individuals were found inside the sporocysts in thetissue of the mussel, which had been allowed to remain in water overnight after it had been dissected, but there were no tails on these individ-uals. However, many of these forms remained alive in containers for48 hours without encysting. Encysted individuals were enclosed by aspherical transparent wall, and they reseml)lcd the cercariae in allstructural details.36 ILLINOIS BIOLOGICAL MONOGRAPHSVI. MONOSTOME CERCARIAEHistory and DefinitionRelatively few of the cercariae described can be placed in this group.Up to the time when Cort (1914) described Ccrcaria urbanensis fromIllinois, only two reports of monostome cercariae were available fromthe literature from North America. Cort (1915) says that they havebeen known since 1817, but I know of no one of them of which thelife history has been proved experimentally. Liihe (1909) described thegroup as: "Ohne Bauchsaugnapf, mit Augenflecken, Schwanz sinfach,lang, schlank, ohne Borstenbesatz. Entwicklung in Redien. Encystierungim Freien (ob bein alien Arten)."None of these monostomes have been known to develop from sporo-cysts, but Looss (1896) states that in material of C. imbricata nearLeipzig he had found rediae in which rediae were developing. A fewforms belonging to this group have been described as having posteriorlocomotor projections on the rediae such as C. imbricata Looss 1893.Some of these rediae also bear peculiar constrictions in their bodies, forinstance, Ccrcaria urbanensis Cort 1914 and Ccrcaria (Glenocercaria)lucania Leidy 1877.Sewell (1922) used the term Monostome Cercariae in its broadestsense, to include "all these forms in which as the name implies, a ventralsucker or acetabulum is missing." Since then experimental life historywork has been done, notably that by McCoy (1929a) on a lophocercousmonostome cercaria, showing that the ventral sucker which has beenabsent in the cercaria, may develop in the metacercaria. Such discoverieshave shown beyond doubt that Sewell's classification of these monostomecercariae is an unnatural one, since many of the forms which he includesin this group are in reality either xiphidiocercariae or furcocercouscercariae. He also divided all monostome cercariae into six subgroupsand named them: Pleurolophocerca, Urbanensis, Ephemera, Lophocerca,Lophoides, and Ubiquita. An analysis of this classification shows groupsUrbanensis and Ephemera to contain only those forms which had beenconsidered true monostome cercariae up to that time. Sewell's Lophocercaand Lophoides groups contain only furcocercous cercariae while hisUbiquita group contains only stylet cercariae. The individuals of hisPleurolophocerca group differ from those of the Urbanensis andEphemera groups in that the so-called oral sucker is really a penetratingorgan or anterior organ similar to that of the furcocercous cercariae;there are no posterior locomotor pockets; the tail has cuticular fin-folds;and there is no trace of any esophagus or intestinal ceca.NORTH AMERICAN CERCARIAE—MILLER 2,7Sewell's Urbanensis group corresponds in the main to the binoculategroup of Faust (1917) and his Ephemera group to the trioculate groupof Faust (1917). For the above reasons, I am limiting the monostomecercariae to Sewell's Urbanensis and Ephemera groups.I find descriptions of the following species that belong to the Mono-stome Cercariae:Binoculate Cercariae1. C. fnh'ociilata Cawston 1911 4. C. kemispheroides Faust 19242. C. konadensis Faust 1917 5. C. yeiwhingensis Faust 19303. C. aurita Faust 1918Trioculate Cercariae1. C. ephemera Nitzch 1807 9. C. robusta Faust 19182. C. hyalocauda Haldemanu 1842 10. C. spatula Faust 19193. C. (Glenocercaria) lucania Leidy 1877 11. C. indica xi Sewell 19224. C. imbricata Loess 1893 12. C. plana Faust 19225. C. monostomi v. Linst. 1896 13. C. trabeculata Faust 19246. C. sostera Sinitsin 1911 14. C. infracaudata Horsfall 19307. C. urbanensis Cort 1914 15. C. triophthalmia Faust 19308. C. pellticida Faust 1917 16. C. leboiiri Stunkard 1932Ccrcaria urbanensis Cort 1914(Figs. 20-27)Physa gyrina hildrethiana taken at Camp Creek near Seymour, Illi-nois, in October, 1931, was found to be infected in unusual numbers witha monostome cercaria, C. urbanensis. Study of this form revealed anumber of interesting facts which have not been mentioned before.Table I, which gives the infection records, will indicate that thisspecies is exceptionally numerous in the above-mentioned vicinity. Hostswere collected also in January of 1932, and great masses of rediae wereobserved in the hepatic tissues. They were elongated sac-like structures(Fig. 26), only 0.263 mm. in length and 0.151 mm. in width in the im-mature stage, 2.25 mm. by 0.63 mm. in a more advanced stage and 3.42mm. by 0.936 mm. in the case of large rediae containing developedcercariae.The almost terminal, muscular pharynx contains noticeable cross-striations in its wall and is spherical in shape. The intestine is large andswollen in most cases (Fig. 24) and the cavity of the body is filled wathwhat appears to be disintegrating tissues and small clear glandularbodies. No living cercariae were seen inside the rediae or in the tissuesof the host in the snails collected in January, although, in a few cases,free cercariae were noted in the water after a mass of sporocysts had38 ILLINOIS BIOLOGICAL MONOGRAPHSbeen separated from the liver tissue. This may indicate that the lengthof infection is definitely limited, either by the seasonal factors or by thelength of life of the rediae, both of which may result in such disintegra-tion of the rediae in the liver tissue. Many of the rediae are greatlyconstricted in one, rarely in two areas (Fig. 25), giving the local regionthe appearance of a neck; also the posterior end, in many cases, is con-stricted, causing a posterior tail-like structure to be present. The intestinehas never been observed extending into this portion.When the snail hosts are kept in containers at room temperatures thecercariae emerge from them in greatest numbers between 8:00 and 9:00in the morning. After this period very few leave the snail and in thelate afternoon and evening the containers, with scarcely an exception,contain only encysted forms. On successive mornings this swarmingis repeated, the snails often being so heavily infected with this form thatthe walls of the containers are literally covered with these cysts. Afterswimming about for a very short time they encyst on the glass, or pre-ferably on water plants and sword grass, while the tail beats with greatspeed, then comes loose and swims about in the water for a long time be-fore finally disintegrating (Fig. 21). The body rounds itself into aflattened circular body and a transparent, stiff covering is formed aboutit. The cyst is formed so rapidly that it resembles the molting processof some animals, but the substance of the wall is probably cystogenousmaterial. By pressing on the cover-slip this cyst is broken and the wormcrawls out. However, I have never observed it to reencyst.Almost all of the body is filled with small granules, refractile, andspherical or oblong, which make the cercaria appear almost black underthe low power of the microscope. The body is also filled with pigmentgranules of a brownish or black color which make a detailed study of itsstructure from the living specimen very difficult if not impossible.Probably the process of cyst formation is not a continuous one,for after the cyst vv'all has been formed it can be seen that there areseveral successive layers (Fig. 22). The body can rotate inside the cystwall and twists about quite readily (Fig. 23). The following are averagesof measurements on five specimens: diameter of cyst 0.232 mm., widthof outer wall 28 /x, width of inner wall 28 /x, total width of cyst wall 56 /x.The tail of the worm is relatively long, as long as the body whileresting normally and much longer when extended for swimming. It has aparenchymatous core, and many striations are present which extend par-allel to the core.The body itself need only be characterized here, for its structure hasbeen carefully studied by other workers. Many other very characteristicNORTH AMERICAN CERCARIAE—MILLER 39features facilitate the identification of this cercaria, namely, the tworelatively large, deeply pigmented eye-spots lateral to and almost on alevel with the posterior limits of the oral sucker; the central eye-spot,slightly smaller, of a more brownish color, but also heavily pigmented;the condensation of pigment anteriorly and laterally; the elongate ovalbody, more pointed anteriorly and subquadrate posteriorly (Fig. 20).The narrow esophagus extends only for a very short distance posteriorlybefore dividing to form the two intestinal ceca which reach almost to theposterior end of the body and extend mesiad to the two large excretoryvessels. The small excretory bladder is at the very posterior end of thebody. The two excretory siphons are large, swollen, sinuous, and filledwith small dark excretory granules (Fig. 20). Posterior locomotorappendages are on the posterior lateral margins of the body on eitherside of the tail base.The two siphons which open into the excretory bladder, extend anter-iorly on either side of the body, and unite in the region of the oral sucker,in the midline of the body, and just anterior to the median eye-spot.No other part of the excretory system could be distinguished in the body,but the tail contains a central longitudinal tubule which connects anter-iorly with the bladder.It is quite probable that the final host of this cercaria exists in someabundance in this stream, since such a high percentage of infection wasfound among the snails collected here. Furthermore, muskrats havebeen noticed several times along the banks and their holes are commonin the banks. They are a likely mammalian host for this parasite, andsince they are largely herbivores the metacercariae would have an easymethod of gaining access into their bodies. This can be confirmed onlyby further studies.Encysted forms or metacercariae were found fastened to the shell ofthe snail as well as on the bottom and sides of the container. The snailswere collected on October 26, 1931, and most of the cysts containedliving metacercariae on January 29, 1932. The cysts are circular objects,flat on their attached sides and convex on their outer surfaces. The coiledtrematode can be seen clearly within (Fig. 23). It is deeply colored by adark brownish pigment, only the anterior end being light in color. Theworm lies in a central cavity and is separated from the cyst wall by a nar-row space. The wall of the cyst is composed of layer upon layer of thin,clear homogeneous material. The animal within has elongated greatlyand deepened in pigmentation. No trace of the two posterior locomotorappendages can be found, but the large granular excretory bladder ismuch larger here than in the free swimming stage.40 ILLINOIS BIOLOGICAL MONOGRAPHSVII. ECHINOSTOME CERCARIAEHistory and DefinitionIn 1909 Liihe placed the Echinostome Cercariae in his LeptocercousCercariae and characterized this Leptocercous Group as follows:Distome Cercarien mit ungegabelten und borstenlosem Ruderschwanze, dessenBreite auch im kontrahierten Zustande wesentlich hinter der des Kdrpers zuriick-bleibt.Liihe designated three subgroups of leptocercous cercariae, one ofwhich was the Echinostome Cercariae, and described the latter as follows:Ohne Bohrstachel. Vorderende mit einem ventral offenen, KragenartigenWulst, auf dem ein Stachelkranz zur Ausbildung gelangt.—SchlankschwanzigeCercarien von Distomen mit dem fiir die Echinostomiden charakteristischen,ventral offenen Kopfkragen, der auch schon bei unreifen, des Stachelkranzes nochentbehrenden Cercarien deutlich kenntlich ist. Reife Cercarien auch bereits mitStackelkranz. Bohrstachel und Augen fehlen. Entwickelung in Redien, die einenvorderen Ringvvulst, zwei hintere seitliche Fortsatze und eine sehr deutliche, dichthinter dem Ringwulst gelegene Geburtsuffnung besitzen. Encystierung in einemHilfswirt.Sewell (1922) devised a rather extensive classification of theEchinostome Cercariae, in which he formed three subgroups: theEchinatoides, the Coronata, and the Echinata. He also included a fourthgroup of cercariae with the Echinostomes, the Megalurous Cercariae, be-cause his study had convinced him of the relationship of this group tothe Echinostomes. However, he does not submit findings which I be-lieve constitute sufficient evidence for such a grouping, so I shall not dis-cuss the megalurous cercariae at this time.Many of Sewell's characteristics which he applies to the subgroupsof Echinostomes can be equally applied to all of these subgroups so thatdefinitive characters of these subgroups are obscured by generalities.Sewell also removed three cercariae from the Echinostome Cercariae sincethey had been described as having no collar spines, even though it hadalready been demonstrated that at least two of these individuals developedspines after encystment. I am speaking of Cercaria agilis Filippi 1857,C. reflexae Cort 1914 and the cercaria of Himasthla militaris Van Bene-den 1861. He also described a new form without the collar spines, C.indica xli.Because of the above-mentioned difficulties in a grouping such as thatof Sewell, I shall not attempt here to use his groups of Echinostomes.Furthermore, a definite designation of all the described larvae into sub-groups seems inadvisable at this time. Several forms that have previouslybeen listed as echinostome larvae must be removed from this groupsince new families have been created in recent years, such as Acantho-stomidae Poche 1926, to include several of the old echinostome genera.Synonomy in the group is common. For instance, the cercaria ofNORTH AMERICAN CERCARIAE—MILLER 41Echinostomum revoliitum has been considered by various authors to beC. echinata Siebold 1837, Ccrcaria A Tsuchimochi 1926, Cercaria No. jNakagawa 1915 and C. limnicola Faust 1924.Faust (1924) attempted to divide these cercariae into ten subgroupsaccording to their excretory systems, but such a grouping is impracticablefor many forms whose flame cell formulae are unknown. Numerouscystogenous glands prevent accurate determination of the pattern ofthe excretory system in many echinostome cercariae.The following forms have been described as possessing no collarspmes:1. Cercaria agilis Filippi 18572. Cercaria of Himasthla viilitarisVan Beneden 18613. C. reflexae Cort 19144. C. fusiformis O'Roke 19175. C. arcuata Cawston 19186. C. complexa Faust 19197. C. pcnihesilia Faust 19218. C. indica xli Sewell 19229. C. senii-robusta Faust 192410. C. pseudo-echinostoiim Faust 192411. C. redicystica Tubangui 192812. C. chitinosto)ua Faust 1930The following forms do possess collar spines but they are all marineforms:4. Cercaria of Echinostouiuni sccu}idnmLebour 19125. C. littorinae obtiisatae Lebour 19126. C. qiiissetensis Miller & Northup 19261. Cercaria leptosonia Villot 18792. C. purpitrae Lebour 19073. C. patellae Lebour 1907fresh-water forms do not include men-18. C. cristacantha Faust 192219. C. chekiensis Faust 192420. C. limnicola Faust 192421. Echinostome Cercaria, Species BTsuchimochi 192622. C. Iiypoderaei conoidei Mathias 192523. C. isidorae Faust 192624. C. eqiiispinosa Brown 192625. C. granitlosa Brown 192626. Echinostome Cercaria, Species ATsuchimochi 192627. Cercaria of Echinoparyphiuni flcxumMcCoy 192828. C. rebstocki McCoy 192929. C. mehrai Faruqui 193030. Cercaria of Euparyphiuni mitriintiitTubangui 193231. C. palustris Chatterji 1933Another form, unique along with C. reflexae in that it possesses afin-fold on the tail, was described by Cort in 1914 as C. trivolvis. Threelarge-tailed echinostome cercariae have been described, unlike the otherechinostomes in regard to their unique tails. They are C. magnacaudaO'Roke 1917, C. caudadena Faust 1921, and C. cita Miller 1929.Descriptions of the followingtion of a fin- fold on the tail:1. C. echinata v. Siebold 18372. C. echinatoides FiHppi 18543. C. coronata Filippi 18554. C. spinifera La Valette 18555. C. number 7 Nakagawa 19156. C. catenata Cawston 19177. C. trisolenata Faust 19178. C. chisolenata Faust 19189. C. acanthostoma Faust 191810. C. constricta Faust 191911. Cercaria of Echinostomum xeiiopiPorter 192012. C. cucumeriformis Faust 192113. C. indica xx Sewell 192214. C. indica xn Sewell 192215. C. indica xxm Sewell 192216. C. indica XLVin Sewell 192217. C. serpens Faust 192242 ILLINOIS BIOLOGICAL MONOGRAPHSCercaria trivolvis Cort 1914(Figs. 28-34)Helisoma trivolvis appears to be particularly heavily infected with thisform in Camp Creek near Seymour, Illinois, and in the St. Joseph Oxbow.Physa gyrina at St. Joseph, Illinois, was also infected.The cercaria moves rapidly, either by crawling or creeping on a sur-face with its suckers or by a rapid lashing of its pow^erful tail, which islonger than the body when it is extended for swimming. The body iselongated, pointed anteriorly, and broadly rounded posteriorly. Whencontracted for swimming the body is 0.280 mm. long and the tail is 0.504mm. long. When only mediumly contracted the body is 0.336 mm, inlength. Under pressure it is 0.448 mm. by 0.280 mm. through the ace-tabulum. When extended the length of the body is 0.549 mm. and ofthe tail 0.616 mm. At its base the tail is 78 /x wide.Under slight pressure narrow fin- folds are noted on the posteriorhalf of the tail (Fig. 28). Without careful study it is impossible to seethe very fine spines which are located on the anterior portions of theworm. A row of thirty-seven alternating spines partly encircles thebody, with a break in the middle of the ventral surface. These spinesare quite long, and point posteriad and laterad, except for the angle spineson the ventral surface near the edge of the break, which point towardthe midline of the body.The oral sucker and acetabulum of this distome are relatively farapart, with no very great difference in size. The length of the oralsucker averages about 65 jx and the width 69 p. when the worm is sub-jected to slight pressure. The acetabulum is 75 /.<, long and 80 ft wide.Both suckers are almost spherical. The oral sucker is followed by aprepharynx which is almost as long as the pharynx. The pharynx is33 ju, by 31 jx. The esophagus is long and reaches almost to the acetabu-lum, which is about 0.169 mm. posterior to the oral sucker. The twonarrow intestinal crura reach almost to the posterior end. The entireesophagus and intestinal crura are filled with connected masses oftissue which enclose open spaces in what will later be the lumen (Fig. 28).This presents an unusual appearance in the living specimen and indicatesthat the digestive system is still non- functional. The acetabulum is about91 /J, from the posterior end of the body.The excretory system is similar to that of most echinostome cercariae.Near the base of the tail on the dorsal side is the excretory pore, andjust anterior to it is the small rounded excretory bladder. The two maincollecting tubules, or excretory siphons, extend anteriad, and near thelevel of the anterior margin of the acetabulum they become greatlyNORTH AMERICAN CERCARIAE—MILLER 43swollen with large, uniform, spherical, two-layered, highly refractiveexcretory granules. These siphons lie intercecally and anterior to theoral sucker, the granules diminishing in number and size anteriorly, andceasing in the region of the pharynx. The characteristic triangular loopof echinostome cercariae is present, and the tubules turn backward andcontinue posteriad, in the immediate vicinity of the siphon, almost tothe posterior end of the ceca, before dividing into secondary tubules.One secondary tubule extends to the pharynx again before it branchesto form capillaries. Flame cells were noted but it is difficult to determinetheir exact connection with the finer branches of the system becauseof the great number of characteristically dark cystogenous glands whichfill the body except in the regions anterior to the pharynx and immediate-ly anterior to the bladder. Another noticeable feature of this excretorysystem is the presence of vibratile elements, throughout almost the entirelength of the descending siphons, particularly active in the region of theacetabulum and above it part way to the oral sucker.One tubule extends posteriad into the tail, which soon divides intotwo lateral branches, each branch extending laterad to the very edge ofthe tail. Cort (1915) describes these branches as opening to the outside.However, I could detect no sign of an opening here. Perhaps theseopenings, functional in the early life of the undeveloped cercaria, be-come closed in the free-living form. Cort states that his material wasoften secured by dissecting the cercariae from the host tissue, andtherefore it is possible that his material difi^ered from emerged cercariaein some respects.The body contains many large cystogenous glands which fill allavailable space in the body. Under pressure they can be seen to extendfrom the oral sucker, to the posterior end of the body, in four ratherdefinite groups or rows. Two rows extend one on either side of thebody, lateral to the main excretory tubes ; an additional row on each sidelies posterior to the pharynx between the esophagus and excretory siphon.They are interrupted by the acetabulum, but, posterior to it, continue tothe end of the ceca. The space anterior to the bladder lacks theseglands. Each gland is filled with elongated refractile bodies arranged inbundle-like formation.Groups of glands, perhaps penetration glands, are posterior to theoral sucker, but distinct tubules connecting them with the anterior end ofthe body were not seen. However, a noticeable feature about thiscercaria is a row of six swollen openings along the anterior lip of theoral sucker, each one of which extends posteriori}^ as a small fiber-likestructure. Each fiber is swollen near the dorsal median side of the oral44 ILLINOIS BIOLOGICAL MONOGRAPHSsucker. Possibly each of these fibers is an undeveloped duct which con-nects with the penetration glands of the worm.Masses of cells which are anterior and posterior to the acetabulum,and connected by a narrow row of cells, constitute the genital cell masses.The tail is much longer than the body when extended for swimming,but under slight pressure is of about the same length. A core extendslongitudinally through the tail, and the tissue next to this core containsa row of large, regularly arranged nuclei as shown by an optical section.They are easily seen in the tail when it is subjected to pressure (Fig. 34).A small fin-fold is limited to the distal part of the tail, and I believe thisstructure has never been described for other echinostome cercariae whichhave an anterior collar of spines. The posterior end of the tail tapersrapidly for a distance of about 0.114 mm., so that the posterior end ispointed. On some specimens there projects from this distal tip a tinyblunt projection, which is more evident with increased pressure, butwhich is only rarely seen. Ultra-microscopic projections or granules arepresent on this structure (Fig. 31) but its exact nature is not known.It is possible that it represents an inverted end of the tail which becomesevaginated under pressure (Fig. 32).C. trivohis develops in rediae which are transparent in the youngstages but are yellow, and finally brown, in their later stages. Theredia is elongated, with narrow posterior and anterior ends, but it variesgreatly in shape according to the degree of extension of the body. Nearthe posterior end of the body are two prominent locomotor appendages,characteristic protrusions extending outward from the body wall andnarrow at their distal extremities (Fig. 30). Posterior to these thebody is narrowed, ending usually in a small knob-like extension, moreprominent when the body is contracted.Near the anterior end of the body, and a short distance posteriorto the sucker, is a broad collar extending around the animal. Whencontracted, the sucker is partly withdrawn in this collar with only itsanterior extremity showing (Fig. 33), but when fully extended a longslender neck separates the collar from the sucker.Just posterior to the collar lies the lateral birth pore, and, underpressure, the cercariae are slowly expelled from the body through thepore (Fig. 29). Under these conditions the pore is situated on a slightprominence. The anterior opening of the cavity of the sucker is terminal,and posteriorly it opens into a rhabdocoele gut which is about one-half aslong as the body. This gut is filled with dark material of a deep reddish-brown color, with the exception of its anterior extremity which is oftentransparent.NORTH AMERICAN CERCARIAE—MILLER 45As the redia develops, its body cavity increases in size, even extendinginto the posterior locomotor appendages, and sometimes contains cercariaeand germ balls in various stages of development.Many of the immature rediae, when contracted, are only 0.347 mm.in length and 0.101 mm. in width, but when extended, measure 0.560 mm.by 62 ^i. The mature rediae are about 0.878 mm. by 0.266 mm. but varyfrom 0.630 mm. to 0.170 mm. in length.C. trivolvis emerges from its snail host in comparatively large num-bers about noon of each day, probably due to temperature increases, butis present in the containers in decreased numbers during the night andearly morning.After swimming about for a time these cercariae enter their snailhost again to encyst, or other snails if they are available. It has beenfound that host-specificity for the encysted cercariae is not very greatfor I have succeeded in recovering them from laboratory raised Helisomatrivolvis, Physa gyrina, Pseudosuccinea, and Succinea.These cysts are transparent, and the worm coiled within is clearlyvisible. The spines are more easily discernible but the penetrationglands are still indistinct.During the summer of 1932, encysted forms of this cercaria werefed to a domestic duck which had been raised in a small pen wherechances of trematode infection were minimized. Fourteen days after thistime, the adult echinostomes were found in the intestine of the duck.Since it was impossible to continue the experiments at that time theexperimental feeding was repeated on a more extensive scale during thesummer of 1933.On July 9, 1933, laboratory raised PJiysa gyrina and one Helisomatrivolvis were placed in a container with a Helisoma trivolvis from St.Joseph which was giving off C. trivolvis in large numbers. On July 14these six snails were examined and a number of encysted forms werefound in each. This material was then fed to a three months old duck.On July 28 the duck was examined and twenty-seven large echinostomeswere found at the lower end of the alimentary tract attached to the wallsof the tract just inside the anus.Later the experiment was repeated ; this time five small Physa gyrinaand two Helisoma trivolvis, all laboratory raised, and previously exposedto emerging cercariae, were fed to a young duck about three and one-halfmonths old. Cysts in one snail were counted and twenty-six were found.After sixteen days mature echinostomes were recovered from the duck.Further studies are in progress concerning this life history and theidentification of the adult, and will be given fully in a later discussion ofits life history.46 ILLINOIS BIOLOGICAL MONOGRAPHSVIII. XIPHIDIOCERCARIAEDefinitionThe cercariae commonly termed xiphidiocercariae represent an im-mense number of forms, differing greatly in their anatomical structure butall having at least one structure in common, namely a stylet. However, itmust be borne in mind that other forms not placed in this group alsohave stylets, for instance, the microcercous and gorgoderine cercariae.Nevertheless, in the xiphidiocercariae this stylet possesses a single sharppoint and sometimes a bulb-like swelling, while in other forms the styletsometimes assumes a complex structure with several points along a ven-tral border, for example in the gorgoderine cercariae.Several authors have described the act of penetration into new hostswhen the cercaria uses the stylet to make an aperture in the tissue, sothat we must conclude that this often functions as a definite penetratingstructure.All members of this large group also possess certain glands, and, asthey seem to have no connection with the stylet, I am using the termpenetration gland which better expresses their true nature. The variousformations which these glands may assume, as well as the nature of theirusually granular contents, are convenient features for specific diagnosis,and workers have utilized this characteristic even for the designation ofsubgroups (Sewell, 1922).Liihe (1909) defined the xiphidiocercariae as follows:Schlankschwanzige Cercarien von Distomen mit einem Bohrstachcl am ab-gerundeten Vorderende. Augen fehlen. Entwicklung in Sporocystcn. Die En-cystierung erfalgt in einem Hilfswirt. Hierher besonders zahlreiche und schwerzu tmterscheidende Arten.The xiphidiocercariae have been subsequently divided into a numberof groups, the members in each case showing certain structures incommon which authors have recognized as showing probable relation-ship. Liihe (1909) recognized only four such groups: Cercariae Micro-cotylae, Cercariae Virgulae, Cercariae Ornatae, and Cercariae Armatae.Lebour (1911) placed some forms in a new group, the Spelotrema, andCort (1915) created another, the Polyadenous Cercariae,Cercariae OrnataeHistory and DefinitionLiihe (1909) created the group Cercariae Ornatae to include twospecies, Cercaria ornata La Valette 1855 and C. prima Sinitsin 1905, andcharacterized it as follows: "Distome Cercarien mit P)ohrstachel, derenschlanker Ruderschwanz einem Flossensaum besitzt."NORTH AMERICAN CERCARIAE—MILLER 47Later Cort (1914) added C. hemilophitra to Liihe's Cercariae Ornatae.Sewell (1922) created a new subgroup, the Prima group, for histwo new species C. indica xxiv and C. indica xxviii and defined thegroup as follows:(1) Distome Cercariae of moderate size in which the acetabuhtni is smaller thanthe oral sucker and is situated behind the middle of the body-length.(2) The tail is shorter than the body and is furnished with a dorso-ventral fin-foldin its distal portion: the ventral portion of the fin extends further forwardsthan the dorsal part.(3) The alimentary canal possesses a prepharynx and a pharynx and the intestinalcaeca reach back to a point between the posterior margin of the acetabulumand the posterior end of the body.(4) Salivary glands are present, and consist of four or five pyriform cells.(5) The excretory bladder is oval or rectangular and the main excretory canalsare dilated in the posterior part of their course and open into the bladderby a common median orifice. The excretory formula appears to be2 X 6 X 1 = 12 flame-cells.(6) Development occurs in oval or sack-shaped sporocysts.Faust (1924) made a second subgroup, the Hemilophura, on thebasis of the excretory system, and placed C. hemilophura Cort 1914 andC. trifurcata Faust 1919 in it. He considered both these forms to havethe flame cell formula 2 [(3 + 3) + (3 + 3 + 3)]. However, McCoy(1929) found that C. hemilophura does not possess this formula and saidit should be removed from the Hemilophura. Thus we have a thirdsubgroup differing from the original two in having an excretory systemof the 2 [(3 + 3 + 3) + (3 + 3 + 3)] type. To this I shall add onespecies described below, namely Cercaria mesotyphla.Since the above groups have been based largely on the character ofthe excretory system, it leaves out of consideration one species of ornatecercaria, Cercaria racemosa Faust 1917. Faust did not give the detailsof the excretory system of this form, but the system is obviously quitedifferent from that of other forms of this group. Therefore, it must beplaced in another subgroup. There are naturally many questions aboutsuch a classification as has been made for this group of cercariae, butperhaps the above will serve to show the morphological distinctions whichvarious authors have pointed out for dififerent individuals of the CercariaeOrnatae.At present the group comprises the following:Subgroup 1. Prima Group Sewell 1922. Subgroup 2. Hemilophura Group1. C. ornata La Valette 1855 Faust 1924.2. C. prima Sinitsin 1905 1. C. trifurcata Faust 19193. C. indica xxiv Sewell 1922 Subgroup 3.4. C. indica xxvni Sewell 1922 1. C. hemilophura Cort 19145. C. longistyla McCoy 1929 2. C. mesotyphla E. L. Miller 1935Subgroup 4.1. C. racemosa Faust 191748 ILLINOIS BIOLOGICAL MONOGRAPHSCcrcaria nicsotypJila E. L. Miller 1935(Figs. 35-40)Physa gyrina hildrcthiana from the Oxbow at Muncie, from CampCreek at Seymour, and from East Lake Eork near Sadorus, were infectedwith C. mcsotypJila. Also P. halci from Alhambra and P. gyrina fromthe Oxbow at St. Joseph and a Pond near Rantoul were parasitized bythis form. Infection is quite prevalent in the Urbana region and wasparticularly high at Rantoul. Hall, in a personal communication, reportedthe same cercaria from the Embarrass River near Urbana.In appearance the body is an oval, narrowed in front and morebluntly rounded behind. It is a rapid swimmer and the tail lashes vio-lently from side to side as it propels the body. In regard to its emergencefrom the host. Hall also states that under constant conditions of light,daylight, and temperature of fifty degrees F., the numbers of cercariaegiven ofif are constant, being approximately two hundred over a twenty-four hour period. A decreasing in the amount of light and temperaturecauses the number of cercariae given off to decrease proportionately.The body is rather small, being only 0.35 mm. long and 0.308 mm.wide through the acetabulum when contracted. In the same state thetail is 0.308 mm. long. When well extended the body is 0.576 mm. by0.196 mm. and the tail is 0.616 mm. long, and 0.308 mm. wide near itsbase.Spines cover the entire body and are directed posteriorly, being moredense near the anterior end of the body.The tail is smooth and without a lumen ; it possesses a noticeable fin-fold near its posterior half (Fig. 35) which decreases in width near theposterior end. It is attached to the body on its ventral surface, justanterior to the posterior end of the body. It is quite muscular and haslongitudinal muscles which are evident when subjected to pressure.There are four groups of these longitudinal muscles which extend in widespirals through the tail, in addition to a deeper circular layer. It will beseen from the above measurements that the tail is as long as, or slightlylonger than, the body of the worm (Fig. ^S). The fin-fold extends alongthe distal two-thirds of the tail.The acetabulum is slightly posterior to the middle of the body and issmaller than the oral sucker. It is circular and measures 60 /x in diameter,when the body is slightly contracted, while the circular oral sucker meas-ures 84 IX in diameter.The cavity of the oral sucker opens into a short prepharynx, about40 /(. long, which connects with a thick-walled, muscular pharynx. Thisstructure is 44 ji wide when it is contracted and only 40 jx long. TheNORTH AMERICAN CERCARIAE—MILLER 49esophagus extends posteriad for a distance of 50 to 80 jx and then dividesto form the intestinal ceca which reach almost to the posterior end. Onthe posterior border of the intestinal fork is a noticeable bulge or sac,which persists, to a lesser degree, even when the worm is greatly extended(Fig. 35). This is a characteristic feature of this species.The stylet points forward and toward the dorsal lip of the oralsucker, and is comparatively small, being only 23 j.i in length. It has aclear hyaline base and its walls are thick, particularly in the region of itsposterior third, and in the anterior portion just behind the point (Fig. 39).Lateral to the esophagus, on either side, lies a group of six styletglands, each of which opens through an individual duct. These glandsare particularly indistinct in this species. The main duct which leadsanteriad from each group of glands is bipartite in nature. After reach-ing the region of the stylet it opens above and anterior to the cavity ofthe oral sucker. These glands do not take neutral red stain as readilyas do those of most other forms which I have examined. Many otherglands are present in the body, particularly from the acetabulum to theoral sucker and along the sides of the body.Dorsal to the ventral sucker are two groups of cells, the germ masses.Both masses lie in a diagonal, dorso-ventral plane and their upper endsare narrowed (Fig. 40). This narrowed portion may indicate the be-ginning of an accessory duct, the oviduct or the vas deferens, since themasses may represent the ovary and testes of the adult.A body which I believe is a ganglion of the nervous system lies oneither side of the pharynx, but the nerves could not be distinguished.The excretory system is characterized by two spherical bladders, ananterior and a posterior one, which fill and empty in a rhythmic manner,and by a flame cell formula of the 2 [ (3 -f 3 + 3) + (3 + 3 + 3)]type (Fig. 36). The two alternately contracting bladders, when filledwith fluid, are slightly different in size, the upper being about 40 /x wideand 20 ju, long, and the lower 30 /x wide by 19 /x long. When the contentsof the posterior bladder are expelled through the pore, the anterior blad-der empties its contents through the median constriction, the processbeing repeated rapidly when little or no pressure is exerted on the worm.The two main collecting tubules proceed anteriad and just anteriorto the acetabulum they divide into an anterior and a posterior branch.The anterior branch on each side gives rise to three branches, one inthe region of the cecal bifurcation, one lateral to the esophagus, and onelateral to the pharynx. Each of these branches divides dichotomouslyinto three capillaries, each ending in a flame cell, the location of whichcan be ascertained by examining the illustration (Fig. 36).The posterior branch on each side gives rise similarly to three groups50 ILLINOIS BIOLOGICAL MONOGRAPHSof flame cells, three in each group, its first division being just posterior tothe acetabulum, the second opposite the anterior bladder, and the thirdlateral to the constriction between the two vesicles of the bladder. Ofcourse the locations of the divisions of the tubules vary slightly withcontraction, but the locations of the flame cells are constant.The above flame cell formula shows why I believe this species shouldbe placed in a subgroup of the Cercariae Ornatae along with C. hemil-ophura Cort 1914.The sporocysts of C. mesotyphla are long, slender sacs of a brownish-yellow color, and vary in size. The larger ones measure about 5.70 mm.in length by 0.43 mm. in width and the smaller ones 3.60 by 0.36 mm.Very little liver tissue of the host remained but great tangled masses ofsporocysts were present. They were twisted almost inextricably aboutone another (Fig. 37), each one having one free end while the other endwas attached to the central mass. The free end often moves slowly backand forth, resembling some algae in this respect, and even contracts andextends, although not to any appreciable degree.Each sporocyst contains cercariae and germ balls in various stages ofdevelopment (Fig. 38). The structure of the immature cercaria isdifficult to see because of many small dark cells which crowd its entirebody. Those forms having the ability to move about in the sporocystwere very active. No birth pore was noted in the sporocyst.Dissection of P. gyrina from Rantoul, Illinois, disclosed the presenceof an infection with cercariae which are identical with the above form inall characteristics which I have noted. However, the sporocysts pre-sented some differences. All five infected snails in this lot containednumerous short sporocysts about 0.592 mm. long by 0.200 mm. wide.This might indicate that these are fairly young sporocysts, even thoughsome of them contained a few mature cercariae.After living more than thirty hours in tap water these cercariae stillfailed to encyst. All attempts to make them enc3^st upon minnows, goldfish, tadpoles, crayfish, and water plants were unsuccessful. I havealso attempted to cause their encystment upon isopods, giant water bugs,and whirligig beetles from the regions of infection, but all attempts wereunsuccessful. Many dead cercariae were noted in the same containerswith these possible intermediate hosts, but no cysts were found.Because the cercaria is so similar in structure to the adult trematode,Glypthehnins quieta Stafford 1900, and particularly because its excretorysystem is identical to that of G. quieta which I illustrated in an earlierpublication (1930), I thought that it might prove to be the larval formof this trematode. My findings have shown that both this larva and theadult G. quieta occur commonly together in different localities in Illinois.NORTH AMERICAN CERCARIAE—MILLER 51The only species with which C. mcsotyphla might be confused isCcrcaria hemilophura Cort 1914. The fin-fold of C. mesotyphla is con-sistently longer than in Cort's form, C. hemilophura; Cort says the wholebody of C. hemilophura contains small cystogenous glands which fill al-most all available space, but I do not find these in C. mesotyphla; Cortalso said he could not distinguish stylet glands in his species ; the bladderof C. hemilophura is club-shaped but has two vesicles in C. mesotyphla;and no blind pouch between the ceca has been described for C. hem.-ilophura. The measurements of C. hemilophura differ from those ofC. mesotyphla.Cercariae MicrocotylaeHistory and DefinitionSewell (1922) believes these forms represent the most primitive ofthe xiphidiocercariae. Liihe used the size of these minute forms toseparate them in his key, but since it is impossible to place many inter-grading forms which have been more recently described, authors havefound it necessary to disregard the size element. However, there areother characteristics for the group which aid in a classification of theseforms. The great majority of them have no digestive system posteriorto the pharynx and the rest have only very short intestinal ceca.Liihe (1909) listed ten species of microcotylous cercariae and definedthe group as follows:Sehr kleine distome Cercarien mit schlakem ungegabeltem Schwanz and mitBohrstachel. Korperlange unter 0.2 mm. Bauchsaugnapf wesentlich kleiner wicder Mundsaugnapt und hinter der Korpermitte gelegen. Stacheldriiscn gering anZahl (2-4), dicfit neben und vor dem Bauchsaugnapf gelegen, haufig von gelblicher,braunlicher oder griinlicher Farbe. Exkretionsblase klein, mit am verbrcitertenVorderende mehr oder weniger deutlich hervortretender Gabelung. Hautbestachc-lung bisfier nur bei eg>-ptischen Arten nachgewiesen, aber wahrscheinlich auch beideutschen Arten vorhanden.3 deutsche Arten scheinen durch verschiedene Form des Bohrstachcls sichcr-gestellt, einige weitere sind unsicher.Cort (1915) improved on the above characterization:1. Developed in gastropods in round or oval sporocysts which arc seldom morethan twice as long as wide.2. Cercariae under 0.2 mm. in length.3. Acetabulum back of the middle of the body and smaller than the oral sucker.4. Stylet glands not more than four on each side and arranged in rows on eachside of the acetabulum.5. Digestive system undeveloped except for a short prepharynx and a smallpharynx.Sewell, working in 1922, divided these forms into four subgroups,namely the Cellulosa, the Pusilla, the Parapusilla, and the Vesiculosa.However, the separation of these subgroups by Sewell's superficial char-acters is questionable.52 ILLINOIS BIOLOGICAL MONOGRAPHSCellulosa SubgroupAlthough Sewell (1922) first used this term and placed in the sub-group C. cellulosa Looss 1900 and C. indica lvii Sewell 1922, he failedto characterize the subgroup, other than to say: "The possession of only-two salivary-gland cells on each side of the body and the simple struc-ture of the excretory system, comprising only four flame cells on eachside of the body, appear to me to be sufficient grounds for creating anew sub-group for this form." Probably the following forms also belongto this subgroup: C. chlorotica Diesing 1850, C. brunnea Ercolani 1850,C. microcotyla Filippi 1854, and C. pseudornata Liihe 1909.I have studied three species of microcotylous cercariae which belongto this subgroup:Cercaria cystorhysa E. L. Miller 1935(Figs. 41-46)Collections of Goniobasis livcscens from the Salt Fork River atHomer, Illinois, in May, 1932, were found to yield large numbers oftiny stylet cercariae, for which I proposed the name Cercaria cystorhysain 1935.A number of features make this form unique among local cercariae.It is very minute and not easily seen with the naked eye, being only about0.140 mm. in length even when extended as it crawls along with the aidof its suckers beneath the cover-slip. During such movement the tail ispulled along without beating from side to side—a characteristic of manystylet cercariae—so that its surface is contracted into folds. The tail isnot more than one-half of the body in length when they are both atrest and it approximates more nearly a third of the body when they arecontracted (Fig. 41).Ordinarily the body of the worm is about 0.140 mm. by 34 /j, whenextended and 73 jx by 56 /x when contracted. However, when the ex-tended worm is quieted by the application of pressure it is 0.140 mm. by50/..The tail is 39 /x long when contracted and 0.140 mm. when extended,but with pressure it is about 43 /x long and 23 /x wide at its base.The longitudinal diameter of the oral sucker is 30 jx and the trans-verse is 27 II while the acetabulum is about 18 /i in diameter. Thesemeasurements were taken when the worm was at rest. The acetabulumis located at a point about 33 /a posterior to the posterior margin of theoral sucker, and it is 39 /x from the posterior end of the body.When swimming, the body is contracted and bent ventrally whiletlic tail lashes back and forth in a jerky, spasmodic movement. AfterNORTH AMERICAN CERCARIAE—MILLER 53swimming for a time the cercaria settles to the bottom of the containerwhere it remains until death.The body is elongated and flattened, and the ends are both broadlyrounded, with the anterior narrow and the posterior subquadrate. Nobody spines were noted on this form.A well-developed oral sucker and acetabulum are present, but thelatter is posterior to the middle of the body and noticeably smaller thanthe oral sucker, being from one-half to two-thirds of it in size. It liesat a point about two-thirds of the body length from the anterior end ofthe worm.A central lumen or core is seen in the tail when no pressure is ap-plied, resembling that of other microcotylous cercariae in this respect.Strong pressure and oil immersion enabled me to see numerous tinyhair-like structures on the distal third of the tail (Fig. 44). A few large,deeply-stained nuclei are scattered through the tail.Located dorsally and in the anterior end of the body is a relativelylarge stylet about 17 ju, in length. It has the characteristic swelling, aswollen circular ridge, at a distance of two-thirds its length from thebase of the stylet. The thickened stylet wall does not extend entirelyto the base of the stylet, but only a thin membrane surrounds this portion(Fig. 43).Lateral to the acetabulum on either side of the body is a pair ofpenetration glands differing from each other in shape and in the natureof their content. The outer gland is more elongate; it consists ofthree lobes or parts but has only one nucleus, and it takes neutral redstain readily. It is granular but cannot be seen clearly without theapplication of pressure. The inner gland is more compact, non-lobed,and contains a large spherical nucleus (Fig. 41). The salivary duct,which contains a granular fluid similar in appearance to that of thetwo median penetration glands, and which is swollen at irregular inter-vals, passes forward, above the oral sucker. These ducts open, one oneither side of the stylet, where granular material exudes, under pres-sure of the cover-slip. This material adheres to the body surface andremains there as globules for a long time.Many nuclear bodies are scattered through the outer tissue of thebody and stain darkly with neutral red.Posterior and to the left of the acetabulum is a crescent-shaped massof tissue which stains a light pink in neutral red; it is probably theprimordium of the reproductive system of the adult worm.The excretory bladder is small and approximately rectangular whennot swollen with fluid. This bladder is prolonged laterally where it givesrise to the main collecting tubes of the excretory system. A characteristic54 ILLINOIS BIOLOGICAL MONOGRAPHSfeature of this bladder when only partially filled is its possession ofanterior and posterior folds or wrinkles (Fig, 42). During contractionthis bladder is rectangular but becomes U-shaped when the body is ex-tended. The folds give a great variety of shapes and sizes to thebladder.The course of the main collecting tubule on each side becomes lost ina coiled mass of tubules just anterior and lateral to the bladder, but ananterior continuation is present, which soon divides into two branches,the anterior of which extends to the region of the oral sucker (Fig. 42).The minute size of this form made it impossible for me to work out thelocation of the capillaries and terminal cells.Cercaria cystorhysa matures in small, oval, or sac-like sporocystswhich occur in great masses (Fig. 46) in the liver tissues of Goniobasislivescens. They are grayish or semi-transparent in color and are filledwith granules and small globules. They vary in shape from sphericalto oblong, many possessing knob-like projections at one end, while someare irregular in outline, with constricted centers. An average of eightsets of measurements shows the oblong forms to be 0.195 by 0.121 mm.,the oblong forms with knobs to be 0.187 by 0.116 mm., those formswith constricted centers to be 0.174 by 0.101 mm. and the spherical onesto be 0.126 by 0.112 mm.Mature cercariae move about inside, but in no case were they seento escape through the walls. No birth pore was noted.No sporocysts were found which contained more than four cercariae,and I have never seen more than two fully developed ones in a sporocyst(Fig. 45). Only one cercaria was found in many of them, but in suchcases the snail hosts had been kept in the laboratory for nearly threeweeks before they were examined.Cercaria meniscadena E. L. Miller 1935(Figs. 47-51)The percentage of infection is higher for this species than for anyother found in Illinois. Large numbers of Pleurocera acuta Raf. werecollected in the Sangamon River near Mahomet, Illinois, in October, 1931,and found to be heavily infected with C. meniscadena. Pleurocera fromOconomowoc River, Wisconsin, was also infected with this cercaria.The worm crawls with the current under the cover-glass, and movesby extending its anterior end and contracting the posterior end as it ispulled forward. It progresses slowly in this manner, the tail being of nouse. When free in the water it has the characteristic, jerky movementof the microcotylous cercariae and moves its body and tail violently.NORTH AMERICAN CERCARIAE—MILLER 55Later it falls to the bottom of the container, where it rests, congregatingthere in great numbers.The body is elongated with a broadly rounded anterior and a narrowposterior end where it is only 18 /x in width. In the region of thepenetration glands and acetabulum the width increases. When well con-tracted the body is about 89 /x long by 66 jx wide. This width was takenthrough the acetabular region. The tail, at the same time, is 59 j-l inlength by 16 /A in width near its base. When well extended for move-ment the body is 0.170 mm. long and the tail 0.150 mm. When at restthe body is 0.117 mm. by 52 p. and the tail is 78 /x by 17 jx. When underpressure of the cover-slip, and slightly contracted, the body is 0.143 mm.by 72 IX and the tail is 0.117 mm. by 17 /x. When well contracted thebody and tail together measure 84 jx in length, when at rest about 0.124mm., and when greatly flattened by pressure 0.224 mm. It can be seenthat the tail is only slightly shorter than the body, whether the cercariais contracted or extended (Fig. 47).No spines can be definitely determined for this form ; however, underimmersion oil, granular-like objects can be noted over the body surface.The oral sucker is well developed and much larger than the ace-tabulum, which is a little posterior to the center of the body. The oralsucker is slightly wider than long, being 33 fi in transverse and 30 /x inlongitudinal diameter. The acetabulum lies about 39 fx posterior to theoral sucker and is 20 ix in diameter. It is about 52 ^u, from the posteriorend of the body. The oral sucker's cavity empties into a tiny pharynx.No prepharynx is present and only a tiny portion of the esophagus wasseen. The remainder of the digestive system has never been observed.The stylet, in the anterior lip of the oral sucker, is 17 /x long and 5 /xwide at its base, while the pointed tip at its anterior end distal to theswollen ridge is 5 /x long (Fig. 47).Two large penetration glands are on each side of the body, theanterior one being in front of the acetabulum and the other being lateralto it. The anterior gland is darker and more coarsely granular, evidentlycontaining a substance of a different nature. Each gland contains alarge clear nucleus. Indistinct bipartite ducts lead forward to theregion of the stylet, where they open to the outside. Lying on each sideof the body, between the ventral sucker and the two salivary glands,is a transparent body which cannot be seen without great pressure. Itpresses against the salivary glands, during contraction of the body, andgives to the posterior pair especially, a crescent shape. The transparentbody contains a single large nucleus. Perhaps this body is a very earlystage of the reproductive glands.The small excretory bladder is rectangular when not fully expanded,56 ILLINOIS BIOLOGICAL MONOGRAPHSbut when extended it is U-shaped, due to the expanded proximal por-tions of the two main collecting tubes. Its pore opens to the outside onthe dorsal surface. In side view this bladder is seen to have consider-able thickness; it measures approximately 26 /x in width and 10 ju, inlength when expanded.The two horns of the U-shaped bladder soon narrow into very finetubules which are so minute and tangled in this cercaria that I was notable to see the connections of their branches with certainty. However,the main collecting tube can be seen to divide in the region of theacetabulum into a posterior and an anterior branch. A division occursin the anterior branch in the region of the salivary glands. No part ofthe excretory system could be seen extending into the tail.The tail has thick walls and a large lumen in its center. Annularconstrictions, which are often present even when the animal is greatlyextended, characterize it. At times the constrictions are annular, par-ticularly when the tail is greatly contracted (Fig. 48) ; again they remindone of spirally twisted ridges extending around the tail. During exten-sion these rings disappear at the base of the tail, the smoothing processcontinuing up to the distal end. About 13 /^ from its distal end is asmall vesicle which sometimes appears when the worm is subjected topressure.C. meniscadena develops in small, swollen, oblong sporocysts which arecharacteristic of the cercariae of the Cellulosa subgroup. They aremassed together in the liver of the host, particularly near its surface.The ends of the sporocysts are bluntly rounded, so that they have anoval appearance in most cases. The nearly colorless wall is very unevenin its thickness, being very thick in some places, while in others it isvery thin but extremely tough (Fig. 49). A central cavity is filled withfluid and contains an abundance of small spherical bodies. Loose strandsof tissue are also present in the cavity.Commonly one, two, and three cercariae are found in the sporocysts,while germ balls are also present (Fig. 50). In many cases disintegrat-ing germ masses are observed. Many sporocysts were also found thatcontained neither germ balls nor cercariae.These sporocysts have no power of independent movement, at leastin their older stages. Mature cercariae move about for hours, pushing theimmature individuals aside in their progress, but none were seen to rup-ture the sporocyst's wall.The sporocysts vary greatly in size and shape ; however, all are ap-proximately oblong or spherical, many with median swellings or terminalknobs (Fig. 51). The average sporocyst is about 0.185 mm. long and0.124 mm. wide. Fifteen specimens were taken at random for thisNORTH AMERICAN CERCARIAE—MILLER 57average. The oblong ones average about 0.205 mm. by 0.127 mm. andthe more spherical ones 0.154 mm. by 0.120 mm. Two or three cercariae orgerm balls were noted in most of the sporocysts but in the majority ofcases only one fully developed cercaria was found.Attempts to induce the free swimming cercariae to encyst in crayfishwere not successful. No cercariae were found encysted in the tissue ofthe snail host.Cercaria cyclica nov. sp.(Figs. 52-53)A number of snails of the species Viviparus georgiana at Leesburg,Florida, were examined in October, 1931, for cercarial infection and twowere found to be infected with a very small stylet cercaria, for whichI propose the name Cercaria cyclica. It is the smallest cercaria that Ihave studied, the body being only 0.126 mm. long when slightly extendedand 66 /x wide through the acetabular region, while the length of the tailis 0.126 mm. When extended for movement the body measures 0.143mm. by 52 ft and the tail is 0.124 mm. long and 18 jx wide near its base.The worms emerge from the snail in large numbers in the earlymorning but emergence soon ceases until the following morning whenthere is another swarming. The body is elongate in shape with a sub-quadrate posterior end, but becomes circular in shape almost immediatelywhen placed on a slide for study (Fig. 52), so that it is impossible tostudy it in its normal, free-living shape. This circular shape is quitecharacteristic, for in less than one minute it has rounded into a flattenedcircle for encystment.The stylet works incessantly at this time, evidently trying to breakthrough the cover-slip. The tail is lost when encystment begins, andsoon it becomes inactive. The worm is an active crawler and makes gooduse of its suckers. No body spines were seen.The oral sucker is large, being slightly more than twice the size ofthe ventral sucker, which is posterior to the middle of the body on asmall projection. No part of the digestive system posterior to the cav-ity of the oral sucker was noted in this form.The tail is of about the same length as the body; a central cavityextends through its center but no part of the excretory system could beseen in it.Many small globules are located mainly in two areas of the body, onearea being just posterior to the large stylet glands and the othersmaller area immediately posterior to the oral sucker.The worm has an unusually large stylet in proportion to the size ofits body, the stylet being 20 /x long and 5 /<. wide at its base. The swol-58 ILLINOIS BIOLOGICAL MONOGRAPHSlen area or shoulder near its anterior end is also very prominent andwell developed (Fig. 52).Perhaps its most noticeable features are the penetration ducts oneach side of the body. In this form there are really two ducts on eachside which are not even connected as are the components of the bl-and tripartite ducts of several other forms. The outer, lighter, andfinely granular duct opens anterior to the other, and connects posteriorlywith a large elongated penetration gland which lies in a transverse posi-tion just lateral to the acetabulum. When the body is contracted thisgland becomes folded, since its anterior end merges gradually into itsduct, giving the appearance of two glands instead of one. The diameterof this duct is not at all uniform, and at one point, about midway inits course, it is swollen into a large, gland-like body, which contains anucleus similar to that in the gland proper. For this reason two of theseglands may be considered to be on each side, instead of only one.The median duct on each side contains larger droplets of materialdifferent from that in the other duct. Anteriorly it ends slightly behindthe anterior end of the other duct, and posteriorly it widens into a largebody just anterior to the acetabulum (Fig. 52). The two inner ductsboth connect to this median enlargement.A small rectangular bladder, which becomes U-shaped when thebody is extended, due to its swollen lateral projections, gives rise to themain collecting tubes. Posterior and lateral to the acetabulum each ofthese tubes divides into an inner secondary tubule which divides intothree branches near the acetabulum, and an outer secondary tubule whichdivides into a posterior and an anterior branch (Fig. 53). The anteriorbranch is greatly convoluted anterior to the acetabular level, but finallycontinues, dividing into three terminal branches lateral to the acetabulum.I believe these are the capillaries of the excretory system but I havenever observed flame cells in this form.After removal of these forms from containers each formed a cystwall. Tapping on the cover-glass caused this wall to break and the wormto crawl out. However, I have never observed these forms to encyst asecond time, for they ahvays died soon after leaving the broken cystw all.Cercariae ArmataeHistory and DefinitionLiihe in 1909 placed a number of xiphidiocercariae in this group be-cause these forms are without a fin-fold and the body length reaches over0.25 mm. He described the group as follows:NORTH AMERICAN CERCARIAE—MILLER 59Distome Cercarien mit Bohrstachel, deren schlanker Ruderschwanz keinenFlossensaum und ungefahr dieselbe Lange wie der Korper besitzt. Korperlange0.25 mm. iiberschreitend. Bauchsaugnapt etwas hinter der Korpermitte gelegenund, wenn iiber haupt, so doch meist nur wenig an Grosse hinter dem Mund-saugnapt zuriickbleibend. Exkretionsblase (soweit bekannt) Y-formig.Hierher anscheinend sehr zahlreiche und schwer zu unterscheidende, bisheroffenbar auch erst zum kleinen Teil unterschiedene Arten.Perhaps Liihe's statement that the species of this group are basedon small differences, indicates the confusion met with in a study of theclassification of these species. He listed ten species as belonging to thegroup but since then many more have been added.Cort (1915) created a new group of xiphidiocercariae and gave itthe name Polyadenous Cercariae, but Sewell (1922), recognizing the factthat size does not constitute a logical basis for cercarial groupings, con-sidered this a subgroup of the Cercariae Armatae, in spite of the smallsize of the two forms which Cort placed with the polyadenous cercariae,namely C. isocotylea Cort 1914 and C. polyadena Cort 1914.Later Sewell divided the Cercariae Armatae into two subgroups, thePolyadenous Cercariae Cort 1914 and the Daswan subgroup Sewell1922. Sewell modified Cort's definition of the polyadenous cercariaeand gave several characteristics of his Daswan subgroup, but the ma-jority of these characters apply equally to both subgroups. However,the forms which Sewell placed in these subgroups, including his newspecies, do not follow his own definitions of the subgroups, the resultbeing, so far as I am able to determine, that only two points in thesecharacterizations are sufficiently constant to form a working basis for theassignment of species to them, namely, (1) that referring to the de-velopment of the cercariae in elongate sack-shaped or filiform sporocystsin the case of polyadenous cercariae and in sausage-shaped sporocystsin the case of those of the Daswan Subgroup, and (2) the characterof the excretory tubules in the two groups.Even here these two points are highly problematical, for many au-thors have not described or figured these sporocysts, and secondly, thecharacter of the excretory system in these minute forms is of such anature that it has never been described in the majority of forms andprobably never will be in many of them because of cystogenous and pene-tration glands which make it impossible to locate already obscure flamecells and capillaries.Altogether there have been well over fifty of these CercariaeArmatae described from various parts of the world. At least twelvespecies from the United States have been sufficiently described so thatthey can be definitely assigned to this group. The list is as follows:60 ILLINOIS BIOLOGICAL MONOGRAPHS1. Cercaria polyadena Cort 1914 7. C. glandidosa Faust 19172. C. isocotylea Cort 1914 8. C. diaphana Faust 19173. C. haskelli O'Roke 1917 9. C. dendritica Faust 19174. C. gregaria O'Roke 1917 10. C. micropharynx Faust 19175. Cercaria of Lissorchis fairporti 11. C. stilifera Faust 1918Magath 1917 12. C. candelabra Faust 19196. C. crenata Faust 1917Several species of Cercaria Armatae have been found commonly inthe Urbana area, as well as at Leesburg, Florida, and Baton Rouge,Louisiana.Cercaria acanthocoela E. L. Miller 1935(Figs. 54-59)This species was found in Helisoma trivolvis from a variety of places,chiefly in the Oxbow at Urbana, the Pollywogs and Oxbow at St.Joseph, and Camp Creek at Seymour, Illinois. It was also found in P.gyrina hildrethiana from Camp Creek, Seymour.It does not remain active for any length of time but soon falls to thebottom of the container where it can be found crawling about among thedebris. In swimming, the entire body is twisted from side to side, thetail lashing even more rapidly, the result being an aimless movement,jerky and unsteady, which does not favor rapid movement in any onedirection for long. When in motion the body is bent into a loop withthe dorsal side outside, and the entire body is somewhat contracted.When it comes in contact with any hard object such as the walls or bot-tom of the container, it progresses by means of its suckers, and, if acover-slip is above it, it prefers to crawl with its ventral side uppermost.As it moves in this manner, the contracted tail is dragged along behindthe body.The body is small and oblong in outline (Fig. 55) with its greatestwidth through the region of the acetabulum when at rest. However, theworm has great powers of extension, extending sometimes until it re-sembles a long narrow ribbon. When greatly contracted it may be moresubquadrate in shape. When subjected to pressure it contracts, theanterior region becoming much wider while the posterior end becomesvery narrow. The anterior end is rather bluntly rounded because oftlie subterminal position of the oral sucker, while the posterior end haspronounced rounded corners because of the presence of setae pocketsor caudal pockets on either side of the tail base. When contracted thebody is 0.228 mm. in length and 0.111 mm. in width, but when extendedit measures 0.355 mm. in length, 85 ft in width. Its length is 0.252 mm.when it is at rest. Neutral red was added to the water to quiet the cer-cariae and then measurements were taken with little difficulty.NORTH AMERICAN CERCARIAE—MILLER 61The body is armed with large spines which are situated in rows thatrun horizontally and diagonally across the body. The spines at theanterior end are quite pronounced but they decrease in size and becomemore scattered posteriorly, until posterior to the acetabulum they arevery small and far apart.The body wall extends ventrally on either side of the tail, whichis attached on the ventral side of the animal near the end of the body.Because of these lateral processes of the body wall, a setae pocket isformed on either side of the tail base, so named because it is open at itsanterior end and bears a group of long setae, or spine-like processes,clearly evident from either a dorsal or ventral view (Fig. 54).The oral sucker is slightly larger than the acetabulum, being 67 [xin diameter when at rest while the acetabular diameter is 58 ^. Theacetabulum is posterior to the middle of the body and, under pressure, orwhen the body is slightly extended, it is at the anterior edge of theposterior third of the body. It is 91 /x posterior to the oral sucker and85 IX anterior to the posterior end. It does not project from the ventralside of the body.Tiny papillae are on the ventral sides of both the oral sucker andacetabulum. These papillae are on the inner, ventral edges of the suckersclose to the margins of their openings. A short distance posterior to theoral sucker is the pharynx into which a short prepharynx opens. It isof about the same length as the prepharynx, but slightly less in severalcases, being only 20 fi long and 23 /x wide while the prepharynx is 23 /xlong. Repeated attempts to see the digestive ceca in the living form wereunsuccessful until neutral red was added to the water containing thecercariae. This makes them visible when great pressure is applied.About midway between the pharynx and the acetabulum the esophagusdivides into two very narrow strands of tissue that represent the futurefunctional crura. For almost their entire course these strands are solidand only in isolated places does a lumen appear. They extend posteriadto a point lateral to the midline of the acetabulum.The stylet, as is usual, is inserted in the dorsal anterior lip of the oralsucker, and is moved about freely by the movements of the sucker'swall. The anterior third of the stylet is cone-shaped, with its pointdirected forward and its basal walls thicker than those of the anteriorend, so that from a side view it appears to have a thickened hump orshoulder on either side of the base (Fig. 56). The posterior two-thirdsis divided into two regions, an anterior part which constitutes by farthe major portion of the stylet and which has reenforced walls of thesame bluish material that is present in the walls of the cone, and a smallposterior portion, darker in color, and solid in texture. It is definitely62 ILLINOIS BIOLOGICAL MONOGRAPHSseparated from the anterior portion and lacks the thickened walls apparentin the rest of the stylet. The stylet is 30 /x long, with its pointed portionor cone not more than 7 ii in length.A group of penetration glands lie lateral and anterior to the ace-tabulum, on either side of the body, the median glands of each group ex-tending mesiad so that sometimes they meet in the region immediatelyanterior to the acetabulum. Repeated efforts to count the glands oneach side gave varying results and led to confusion until it was finallydetermined with certainty that the same number of glands was notalways present. This is interesting in that it is contrary to the condi-tion in many other cercariae with regard to this character. It is oftenregarded as a character of great specific value in the identification ofspecies but it is to be noted here that we must make allowance for thisvariation. Pressure enables one to see all of the glands clearly, each withits own nucleus, since they are all brought to the same level. Seven oreight glands are located on each side—only rarely are there six or nine—the median ones meeting in the midline.A pair of ducts, two on each side and in close proximity, extendanteriad to the side of the stylet where they open to the exterior. Thetwo ducts on each side twist about each other. This, together with thefact that they possess numerous swollen areas throughout their lengths,differentiates them from many other forms similar to C. acanthococla.Many small glands fill the body, both anterior and posterior to theacetabulum, each with a dark nucleus when in neutral red. A compactgroup of small cells lies between the oral sucker and the pharynx.Lateral bodies are thought to be cystogenous glands.Two cell masses are present which are the early stages of the repro-ductive organs. One lies just posterior to the acetabulum and the otheris just anterior to it. They are connected by a narrow strand of cellsextending postero-laterad around the acetabulum.Normally the excretory bladder, because of a constriction in its an-terior region, consists of a posterior or caudal vesicle which opensanteriorly into a narrow lumen, and two lateral vesicles or arms withwhich this lumen connects. The walls of these arms, or bases of themain collecting tubules, are flexible so that they become periodicallyswollen with fluids (Fig. 54). This gives the appearance of three blad-ders in this cercaria, an important characteristic in identifying it if thefunctioning of the various parts is understood. The connections betweenthese parts of the bladder are difficult to see when no pressure is applied(Fig. 57). Periodically the two lateral vesicles connect so that at this timethere appears to be a single bladder, which extends horizontally. Thefluids are then forced toward the center so that a median anterior vesicleNORTH AMERICAN CERCARIAE—MILLER 63is formed, resembling greatly the above-mentioned caudal vesicle. Thefluids are emptied posteriorly and fill up the caudal vesicle from whichthey are emptied to the outside through the excretory pore. This lieson the dorsal surface near the base of the tail, a short distance anteriorto the posterior edge of the body. Under strong pressure the connectionsbetween these bladders all become widened so that the bladder is broadthroughout its entire length and resembles a large Y. When the medianpart is sharply constricted the bladder appears to consist of an anteriorV and a posterior rectangle. Thus the bladder assumes a great varietyof shapes during its functioning and with varying degrees of pressureexerted by the cover-slip.A main collecting tube extends anteriad from each arm of thebladder, and divides lateral to the acetabulum into a posterior and ananterior secondary tubule. The anterior tubule has four branches,and the posterior one two branches, each branch ending in three capil-laries. Thus there are eighteen capillaries in each side of the body,twelve anterior and lateral to the acetabulum and six posterior to it. Ofthe anterior branches, one is lateral and slightly anterior to the acetabu-lum, one is lateral to the esophagus, one is lateral to the pharynx, and thefourth is immediately posterior to the oral sucker. The anterior branchesof the two posterior ones are lateral to the median constriction of thebladder, and the posterior branch is in the extreme caudal portion of thebody lateral to the setae pocket. Only four flame cells were identifiedbut no doubt each capillary ends in one of these terminal cells.The tail is usually contracted as it is pulled along by the animal.Since it has great powers of extension, large folds occur along its sideswhen contracted, but no fin-fold is present. When free from pressure,a lumen or core can be seen extending through the center. Scatterednuclei are present in the tail, an average of fourteen being there for fourspecimens studied. The width near the base of the tail is 36 /<,. Whencontracted it is 0.117 mm. long and when mediumly extended it is 0.247mm. long.Nearly all of the liver tissue of the snail host had disappeared and thesporocysts were present in great tangled masses. These sporocysts areelongate, sac-like structures (Fig. 58) and vary a great deal in size andshape, depending on their age. The length varies from about 0.2 to0.78 mm. and the width from 15 ft to 0.24 mm. The walls are thin andprolonged into knobs and swellings at various points. Cercariae, whenmature, travel rapidly from one end of the sporocyst to the other andoccasionally break through a tiny opening at one end of the sacwhich they have made by their own efi:"orts. They squeeze slowly through64 ILLINOIS BIOLOGICAL MONOGRAPHSthis opening and swim actively away. At least in the older stages thesesporocysts have no power of independent movement.Immature cercariae in a single sporocyst range from ten in numberto one hundred and fifty.In one large reddish-brown pigmented sporocyst a large quiescentcercaria was observed. It acted much as an encysted individual, had nostylet, was as large as, or larger than, the metacercaria of this form andresembled the metacercaria in anatomical respects, but had a small un-dersized tail which moved only slightly. This cercaria was nearly aswide as the sporocyst and appeared to be a giant individual among itsfellows. Whether it represents a dual infection of the snail or a phe-nomenon as yet unexplained in the life history of Cercaria acanthocoelaremains to be solved. I believe that this represents a cercaria that forsome reason has failed to encyst.Encysted individuals were taken from cysts in the liver tissue ofthe snail host (Fig. 59), but their scarcity indicates that in the majorityof cases the cercariae do not return to encyst there.When the transparent cyst wall was broken the worm moved aboutfreely. The intestinal ceca are readily visible, reaching nearly to theposterior end of the acetabulum, and are noticeably wider and moredeveloped than in the cercaria. No stylet was present but it was noticedin the wall of the cyst before the cyst was broken. The bladder isfilled with granules and is truly Y-shaped. Spines are about evenlydistributed over the entire surface of the body, and can be easily seennow. The body is about 0.280 mm. by 0.123 mm. and the distance be-tween the oral sucker and the acetabulum is 61 /.i. The acetabulum is 52 /xin diameter and 81 ju, anterior to the posterior end of the body. The oralsucker is 69 fi wide and only 57 /x long.Attempts to recover encysted individuals of this form from severalspecies of fish, crayfish, and a number of frogs, were unsuccessful.However, cysts were found on Notropis whipplii Girard, sixteen hoursafter cercariae had been placed in the dish containing the fish. Thesecysts were fed to turtles, but with negative results.C. acanthocoela differs from similar forms in several respects. Itcannot be confused with C. isocotylea Cort 1914 because of the unde-veloped digestive tract in C. isocotylea as shown by Cort (1914) andFaust (1918a). C. polyadena Cort 1914 has no esophagus or digestivececa and has from ten to twelve penetration glands. C. glandulosaFaust 1917 differs radically from this form in the size of its stylet, thecharacter of its excretory system, and the possession of numerous glandsabout its digestive tract. C. diaphana Faust 1917 differs from C.acanthocoela in the nature of its anterior glands, the proportions of itsNORTH AMERICAN CERCARIAE—MILLER 65two suckers, and the nature of its excretory system. Finally, C. indicaXVII Sewell 1922 differs markedly from C. acanthocoela in regard to itsexcretory system, the size of its stylet, and its genital cell masses.Cercaria tricystica E. L. Miller 1935(Figs. 60-65)This xiphidiocercaria was found in Ilclisoina lanlnm at Baton Rouge,Louisiana. Collections were made in June, 1932.The body is bent ventrally and the tail lashes violently as the wormmoves through the water. Soon the cercariae sink to the bottom of thecontainer where they congregate in large numbers.The body is ilattened dorso-ventrally, much like that of Cercariamcsotyphla, and is oval in outline. When contracted or at rest the bodyis widest just anterior to the acetabulum. When at rest it is 0.224 mm.by 78 IX, when well extended 0.308 mm. by 56 /i and when contracted0.196 mm. by 0.112 mm. The greatest width of the body when contractedis about 0.124 mm.Spines are present at the anterior end of the body but they becomesmaller and more scattered posteriori}-, until, posterior to the acetabulum,they cannot be seen.The suckers are disproportionate in size, the oral sucker being largerthan the acetabulum. It is about 52 /x in length and 59 /<. in width whenat rest, while the acetabulum is only 39 ft in diameter. The acetabulumis posterior to the middle of the body, being about 65 /x posterior to theoral sucker and 59 ^i anterior to the posterior end of the body. It islocated at the division of the median and posterior thirds of the body.The ventral sucker does not project ventrally as is common in manyof these forms.A short prepharynx and relatively large pharynx lead from the oralsucker. This pharynx is about 20 /i long and 20 /x wide. Posterior to itextends the narrow esophagus, which soon divides to form the equallynarrow crura. They extend posteriad to about the horizontal diameterof the acetabulum (Fig. 60). These crura contain very narrow lumens,with numerous cell-masses, indicating that they are still undeveloped.The mucin glands constitute a noticeable and distinctive feature ofthe cercaria (Fig. 61). Each lateral group is composed of nine glandswhich lie in the dorsal region of the body and lateral to the acetabulum.Each gland contains a large clear nucleus. All of the glands on eachside connect anteriorly with a large lateral duct. In its posterior regionthis duct is bipartite but near the oral sucker each duct is composedof four separate parts (Fig. 60). Each duct opens at the side of thestylet, anterior to the walls of the oral sucker. Under pressure asticky material passes out through the openings of these ducts.66 ILLINOIS BIOLOGICAL MONOGRAPHSThe stylet is about 21 /x long and contains a dorsal ridge or swellingnear the base of its anterior third (Fig. 62). A side view of the styletindicates that this ridge does not extend ventrad (Fig. 63.)A genital mass, which stains pink in neutral red, lies posterior tothe acetabulum and extends to the right, passing forward along theright side of the acetabulum. It is composed of small spherical cells.The excretory bladder varies in its shape because of pressure andcontraction of the excretory pore. However, when not distended withfluid it often consists of three vesicles, because of a median constrictionwhich separates the two lateral arms from the posterior vesicle. Thisconstriction is weaker at times so that a broad T is formed. Whenthe body extends this shape changes to a Y. The constriction is so minutethat three separate bladders seem to be present. In this respect it re-sembles C. acanthocoela.A main collecting tubule extends anteriad and laterad from eachlateral vesicle and, lateral to the ventral sucker, divides into an anteriorand a posterior secondary collecting tubule. The connections of the finerbranches of this S3^stem have not been determined.The tail is attached ventrally as noted above, and when the worm isnot swimming the tail is contracted and has an irregular outline. Itis much shorter than the body, being only 84 /x long when contractedand 34 fx wide at its base. When slightly extended it is 0.140 mm.long and when well extended it is 0.174 mm. long. Very narrow caudalpockets are present because of the above mentioned tail attachment butthey are not readily seen. No setae are present in these pockets as istrue of the pockets of C. acanthocoela. No caudal excretory tubule isvisible but a narrow lumen is present in the tail which can be observedwithout the application of pressure. The tail has no fin-fold (Fig. 64).C. tricystica develops in the liver tissue of Helisoma lantum whichis crowded with very small oblong sporocysts, similar to those of C.meniscadena. In old infections I have never found more than one fullydeveloped cercaria in a sporocyst (Fig. 65), but in the young formsseveral fully grown as well as numerous developing cercariae werefound. The sporocysts possess transparent walls, but the walls of thosecontaining active cercariae may contain a light golden-brown pigment.The wall is elastic and easily distorted by the cercariae within. It is thinand composed of large cells joined to each other in an irregular forma-tion. Large individuals were 0.273 mm. long and 0.137 mm. wide butthe averages for ten individuals were 0.195 mm. in length and 85 /x inwudth.Cercaria. tricystica differs from both C. isocotylca and C. polyadenain the relatively small size of its tail, the shape and size of its sporocysts.NORTH AMERICAN CERCARIAE—MILLER 67the number of salivary glands, the possession of a complete digestivetract, and in several characteristics of less importance. It is unlike C.diaphana in that C. diaphana has caudal pockets lined with setae, astylet nearly twice as large as that of C. tricystica, and eight penetrationglands of much smaller size. The only other forms at all like C.tricystica are C. glandidosa and C. indica xvii. C. glandnlosa containsnumerous glands which line the digestive system ; it also has pronouncedcaudal pockets which have spines as does C. diaphana, and it has a styletlarger than that of C. tricystica. C. indica xvii has pyriform salivaryglands which differ in number and in the character of their ducts fromthose of C tricystica.Cercaria cystoncluioidcs E. L. Miller 1935(Figs. 66-70)Ampullaria depressa, collected at Leesburg, Florida, in October, 1931,was found to be infected with a very large st3det cercaria. The cercariaeand sporocysts were present in the liver in immense numbers, suchswarms of cercariae emerging that they soon made the bottom of thecontainer white, when they began crawling about with their suckers.They continue their movements long after the tail has been lost. Theyremained alive in the containers for a period of thirty-six hours.The body is elongate, bluntly rounded at its posterior end and drawnout to form a narrow projection at its anterior end (Fig. 68). A de-pression occurs at the posterior end of the body in which the tail isattached. The body is about 0.616 mm. long and 0.325 mm. wide whenat rest. This width was taken through the acetabulum. The tail isabout 0.504 mm. long when at rest. Thickh-set spines cover the entirebody surface and are larger in the anterior region.The large stylet is about 36 ji long and bears a swollen area, or ridge,at the base of its pointed anterior end (Fig. 67).The tail, which has almost the same length as the body, has no ex-cretory tubule, but its longitudinal core disappears when the tail isfully extended (Fig. 66). It possesses no fin- fold.Numerous glands make obscure the excretory tubules in this formand many tiny globules are present through the entire body.The penetration glands lie anterior to and on either side of theacetabulum, each lateral group consisting of a large number of glandsso that I was not able to determine the number. The large penetrationduct can be seen extending along either side of the bod}^ to its termina-tion at the anterior end of the body near the base of the stylet. Thistermination is swollen, the enlargement being particular)}^ noticeablewhen the worm is resting or is contracted.68 ILLINOIS BIOLOGICAL MONOGRAPHSThe oral sucker occupies an antero-ventral position, being not quitesubterminal. It is circular, being about 0.101 mm. in diameter. Theacetabulum occupies a position ver}' near the center of the longitudinalaxis of the body but slightly posterior to it. It is unique in being slightlylarger than the oral sucker, for it is about 0.104 mm. in diameter. Thebody extends 18 /^i anterior to the oral sucker and 0.182 mm. posterior tothe acetabulum. The ventral sucker is 74 ^i posterior to the oral sucker.Tlic cavity of the oral sucker, opening posteriorly into a short pre-])harynx which is continued posteriorly into a muscular pharAmx, measuresabout 0.299 mm. in length and 0.351 mm. in width when quiescent. Therelatively short esophagus divides to form the intestinal crura whicliextend posteriad as narrow lateral tubes, reaching almost to the posteriorend of the excretory bladder (Fig. 69).The large excretory bladder opens througli a dorsal pore to the ex-terior. It is rectangular when in a contracted condition, but when filled,it extends anteriorly as a large cone-shaped or pyriform vesicle, reachingto within a short distance from the acetabulum, where it divides into twoantero-lateral siphons.A mass of cells Avhich probably represents the genital primordiumlies posterior to the acetabulum.Each siphon crosses the cecum and divides just anterior to the acetabu-lum, into an anterior and a posterior secondary tubule (Fig. 69). Theposterior branch divides ultimately into three branches, each branchof which ends in three capillaries, each with its Hame cell. The flamecells, M"hich are constant in position, total thirty-six, eighteen on eachside of the body. The anterior secondary tubule divides similarly intonine such collecting tubules. The anterior group of flame cells lieslateral to the oral sucker, prepharynx, and pharynx ; the second group isin the immediate region of the union of the intestinal ceca ; the thirdgroup is in the region between the second group and the acetabulum ; thefourth group is lateral and posterior to the acetabulum; the fifth groupis lateral to the excretory bladder ; and the sixth group is lateral andposterior to the excretory bladder.Upon opening this infected AmpnUar'ia dcprcssa, I found the liver tobe bulging with thousands of cercariae and sporocysts in all stages of de-velopment. The excretory tubules and the bladder were not seen in thevery young cercariae.These sporocysts were quite heavily pigmented with a brownish-red pigment. Slight movement could be noted at the knob-like endsbut the swollen portions, at least in the older individuals, exhibited nonewhatever. The majority of the sac-like sporoc3'sts have two swollenareas filled with cercariae, and a neck-like constriction between them(Fig. 70). In many of the younger sporocysts only one of these swollenNORTH AMERICAN CERCARIAE—MILLER 69areas is present. Matured cercariae are actively engaged in strikingagainst the walls of the sporocysts with the stylet, and occasionally oneescapes through the opening made in this wall. Germ balls in variousstages of development are also present in large numbers.This species represents one of the few forms ever described fromFlorida, and no Cercariae Armatae have ever been described which mightbe confused with it because of close similarity in structure. Its largeacetabulum sets it apart from most other related forms. A few ofthese cercariae have been described which also have a larger ventralsucker than oral, such as Cercaria tenuispina Lijhe 1909 and Cercariatriloba Filippi 1857, but confusion can be avoided because of other differ-ences between these forms.Cercaria stcganococla E. L. Miller 1935(Figs. 71-73)The host of this species of cercaria is PJiysa gyrina hildrcthiana whichwas collected at Camp Creek near Seymour, East Lake Fork near Sa-dorus, and in the Drainage Ditch at Urbana. Material was obtained inApril and May, 1932. Scarcity of material gave me no opportunity tomake detailed studies of several features.This form resembles C. acanthococla and casual observation gives onethe impression that it is C. acanthococla. However, several differenceswill be mentioned.It is an elongated stylet cercaria, having the jerky movement cliar-acteristic of these forms, as it swims through the water.The body is narrower near its posterior end, and a little anterior tothe posterior margin on the ventral surface of the body is the attach-ment of the tail. A deep groove on this surface into which the tail fits,gives rise on either side of the tail base to a deep caudal pocket whichhas its lateral wall lined with small spines, directed inward (Fig. 71).Many spines are on the anterior end of the worm. They becomesmaller and are more scattered posteriorly until, in the region of the ace-tabulum, they are not visible.The body and tail are of about the same length. With oidv littlepressure the body is 0.224 mm. long and 0.168 mm. wide when contracted.When at rest both the body and tail are about 0.280 mm. in length, andthe tail is 45 n wide at its base. However, when well extended the bodvmay be 0.460 mm. by 80 //.. The tail is pulled along as the cercariacrawls, beating vigorously when body movement occasionally ceases. Alumen is visible when the tail is not compressed. No fin- fold has beenseen on the tail.The penetration glands are peculiar in that in addition to a group offive to six glands on either side of the acetabulum, there are a few small70 ILLINOIS BIOLOGICAL MONOGRAPHSglands attached to the side of the ducts (Fig. 71), Two small glandsare usually thus attached on each side but their position is so indistinctthat it is impossible to determine their number with certainty. Thelarge duct on each side of the body is twisted and swollen at intervals.It is narrower near the posterior border of the oral sucker, then swellsand from here on to its anterior opening is tripartite. Just before open-ing to the exterior on either side of the stylet the ducts narrow rapidlyand become very fine tubules, still, however, retaining a median striation.Droplets of a thick consistency form at the openings of these ducts whenpressure is applied to the animal. Other small glands cover the body.Small flattened masses of cells which represent the undevelopedgenital system lie anterior and posterior to the acetabulum (Fig. 71).The oral and ventral suckers are approximately of the same size.The length of the oral sucker averages 69 /a and its width 66 ix, whilethe ventral sucker is 67 fi by 65 /a. When the worm is at rest these twosuckers are spherical. The acetabulum is in the center of the body, at adistance of 70 ^ from the anterior end and 0.104 mm. from the posteriorend of the body. It is 98 /x. behind the oral sucker.The stylet contains the characteristic thickening of cercariae armataenear the base of its anterior third (Fig. 72). This thickening does notextend ventrally as determined from side views. Near its base thethickened walls cease at a circular constriction and the stylet ends in aglobular base which is enclosed in a thin wall and is composed of a homo-geneous hyaline substance. The stylet averages about 27 ^u, in length butoccasionally reaches a length of 30 p..Posterior to the oral sucker is a very short prepharynx which some-times does not show. Posterior to it is the pharynx, an esophagus, andfinally the two intestinal crura, which extend to within a short distanceof the posterior end, almost to the back margin of the posterior excretoryvesicle if the worm is not fully extended. These crura are very narrowand rudimentary and can seldom, if ever, be seen in the living animalunless it is stained with neutral red or a similar stain ; then the wormmust be subjected to great pressure. The tissue inside the walls of thecrura stains deeply with neutral red and this material is seen to fill thelumen only at irregular intervals (Fig. 71). The development of this di-gestive system is an important difterence between this form and C.acanthocoela, and constitutes one of the few useful characters in a sepa-ration of the two species.The expulsion canal is composed of the following elements: a posteriorrectangular vesicle which connects with its excretory pore by a narrow,short tube that opens at the base of the tail on its dorsal side; a medianNORTH AMERICAN CERCARIAE—MILLER 71anterior constriction which extends forward for a short distance be-fore dividing to form a Y; and, finally, two lateral elongated vesiclesposterior and lateral to the acetabulum which are really expanded por-tions of the basal ends of the main collecting tubules. These bladdersoften communicate with each other by forming a broad, transverse,single vesicle just before emptying into the posterior vesicle through theconstricted anterior end of the median expulsion canal. Again, allthree may be broadly joined so as to make a typical Y-shaped bladder.The bladder functions much as it does in C. acanthocoela. Main col-lecting tubules extend anteriad from these lateral bladders but the con-nections of the finer tubules and capillaries of the excretory system havenot been determined.Large, elongate, irregularly-shaped, yellowish sporocysts are foundin the liver tissue of the host (Fig. 73). They are filled with manycercariae in different stages of development, from undifferentiated germballs to mature cercariae seeking a way out of the sporocyst. Olderinfections were noted in which the liver seemed to be disintegrating eventhough the snail was still alive. In these snails the tissue was soft andbroken but still filled with active cercariae. Many old, partially disinte-grated sporocysts were found in these snails. It may be that when thecercaria is parasitic in several different species of snails, the more uncom-mon hosts are not able to withstand heavy infections, so that there is anactual disintegration of the liver, with the consequent death of the sporo-cysts. Disintegrating germ balls were also present. The average di-mensions for ten of these sporocysts were a length of 4.5 mm. and awidth of 0.252 mm.While the digestive system of C. steganocoela is similar to that ofabout fourteen other species of these Cercariae Armatae, other differencessuch as the number of salivary glands on a side, the shape of the excre-tory bladder, the presence of large caudal glands, and the character ofthe genital masses enable me to differentiate it readily from these forms.I refer to such forms as the following: C. stylobuccalis Faust 1922, C.microxiphifera Faust 1926, C. paracephaladena Faust 1926, C. cazvstoniFaust 1919, C. ingracilis Faust 1921, C. Jmmilis Faust 1921, C. cephala-dena Faust 1921, C. tennispina Liihe 1909, C. triloba Filippi 1857, C.limnaeae ovatae v. Linstow 1884, C. secunda Sinitsin 1905, C. dimorphaSinitsin 1911, and C. cribrata Sinitsin 1911. C. candelabra Faust 1919,the only North American form described up to this time which re-sembles C. steganocoela most in regard to the digestive system, differsfrom it in having an excretory bladder very different in shape, a smalleroral sucker, acetabulum and stylet, and in having a cluster of penetrationglands on each side of the body with many in each cluster, while thereare only from five to seven on a side in C. steganocoela. C. pseudarmata12 ILLINOIS BIOLOGICAL MONOGRAPHSBrown 1926 has only four penetration glands on each side, and C.leptosoma Brown 1926 has five.It should be noted here that synonomy may be the result of earlierdescriptions of forms in which no digestive system was seen beyondthe pharynx, for improved methods have probably enabled workersto see structures whicli were not seen by earlier workers. This has beendiscussed earlier in tliis paper.Cercaria pachycysiata E. L. Miller 1935*(Figs. 74-77)Jlclisoma Irivolvis collected at Camp Creek near Seymour, Illinois,in (Jctober, 1931, and at Mud Slough near Henry, Illinois, in June, 1932,was found to be infected with a small xiphidiocercaria belonging to theCercariae Armatae. A detailed study in 1935 convinced me that this wasa new species of cercaria.Measurements were difficult to make on this worm since it was con-tinually in motion, until the pressure of the cover-slip was great enoughto distort the worm, or until stain such as neutral red or methylene bluehad been added to the water. It crawls aimlessly about ; the contractedtail is pulled along, and at intermittent periods it is extended and beatsrapidly from side to side, as occurs commonly in the Cercariae Armatae.The body is usually an elongate, tlattened oval, but ribbon-like whenwell extended. The anterior end is narrower than the posterior end,which is broad and truncate. The posterior end is elevated dorsall}^ soas to make a hump above the ventral attachment of the tail. The smallacetabulum does not protrude ventrally. Many small oil-like droplets,bluish in color, are distributed through the body, and give this cercariaa distinctive appearance. Numerous small spines are on the anterior endof the worm, but they thin out posteriorly so that they do not reachbeyond the acetabulum.The length of the tail averages about one-half that of the body. Thetail is inserted on the ventral side of the body a short distance from theposterior end. When it is contracted there is a dark area in its centerwith occasional droplets and groups of cells scattered through it. Thetail has no fin- fold and no caudal excretory tubule. Few nuclei arepresent in the tail. The ratio of the body length to the tail varies withcontraction. All width measurements were taken through the region ofthe acetabulum. With faint pressure the contracted body is 0.129 mm.!jy 0.168 mm. and when extended it is 0.392 mm. by 73 /t. Measurements*Since the publication of the abstract of this monograph in 1935, the writer has found thatCercaria tetradena E. L. Miller 1935 is a homonym of Cercaria tetradena Faust 1924. Refer-ences to this species elsewhere in the present paper have been changed to C. pachycystata, asthe writer is here proposing the name C. pachyi. ystata for C. tetradena E. L. Miller 1935.NORTH AMERICAN CERCARIAE—MILLER 73taken to show the ratio of the tail and body length showed the quiescentbody to be 0.336 mm. by 0.157 mm. when pressure was used. At thesame time the tail is 0.169 mm. by 30 jx. These measurements show thetail length to be about half that of the body. The greatest length notedis that of 0.47 mm. for the body and 0.28 mm. for the tail when they wereboth fully extended.The stylet has thick walls which become thinner in its pointed anter-ior cone ; however, it lacks the pronounced swelling or ridge which isso common to those forms which we speak of as Cercariae Armatae. Itslength averages 16 /.i and its distal two-thirds consists of a hard, thickenedouter covering, which comes to a point grackially (Fig. 76). It is in thedorsal lip of the oral sucker.The oral sucker is located almost at the tip of the body. Prominentcircular muscle fibers line the cavity of the sucker. The two suckers areequal in size, averages showing the diameter of the oral sucker to be 59 /x,that of the acetabulum to be 52 /i. Under medium pressure the ace-tabulum is about 0.13 mm. posterior to the oral sucker and 0.153 mm.anterior to the posterior end of the body. A long prepharynx, 30 /x long,a comparatively large pharynx, 23 jx by 34 /.<., and a short esophagus arepresent. Near the acetabulum the esophagus divides into two narrownon- functional crura which extend posteriad almost to the end of thebody and slightly posterior to tlie excretory sphincter (Fig. 74). Onlyby persistent pressure, staining, and use of oil immersion, can one seethese in the living form.Two large ducts extend posteriad from the anterior dorsal marginof the oral sucker and connect with a group of four large glands oneach side of, and anterior to, the acetabulum. Each duct consists of threelarge strands clearly separated for some distance at their anterior end.Near the edge of the oral sucker the three strands unite or at leastbecome twisted about each other, but finally widen again before theyconnect with the salivary glands. A group of closely-packed, very smallcells or glands are also located along the ventro-posterior edge of tlieoral sucker.The excretory bladder is uiuisually complicated. Just anterior tothe union of the ventrally attached tail is a large sphincter possessingvery thick walls and hair-like structures on its inner postero-lateral walls.It empties into a narrow canal which extends to the posterior end of thebody above the tail base and opens to the exterior at the end of thebody between it and the tail. Anterior to this sphincter extends a thick-walled canal, the posterior portion of which periodically expands into abladder during the functioning of the expulsion canal. This canal isirregular in its course during contraction. Just posterior to the aceta-74 ILLINOIS BIOLOGICAL MONOGRAPHSbulum it expands into another transverse vesicle which is about as wideas the acetabulum (Fig. 77). The lateral portions of this vesicle pulsate,forcing liquid down the lumen into the posterior bulb of the bladder.Each lateral bulb connects laterally with a main collecting tubulewhich, at its lateral extremity, divides into an anterior and a posteriorsecondary collecting tubule. Each secondary tubule has three branches,the anterior branch of the posterior tubule being directed forward whilethe posterior branch of the anterior tubule is extended posteriad (Fig.77). Each branch, at least in the posterior half of the body, divides intofive capillaries. However, the penetration glands and other materialin the anterior half of the body make it difficult to determine the numberof capillaries and flame cells there.A single genital mass lies immediately posterior to the acetabulumand is composed of minute cells which stain pink in neutral red.The mature sporocysts have walls containing much orange or brown-ish pigment, and they fill all available space in the liver of the snail (Fig.75). They are elongate sacs with blunt ends and thin walls, and con-tain many cercariae in various stages of development. The sacs are notfiliform in the sense of having a length at all comparable to that of thesporocysts of C. mesotyphla.Various features of the excretory system, the salivary glands, genitalmass, and digestive system of this species differ sufficiently from alldescribed species to verify my statement that the above form is a newspecies. While C. acanthocoela, C. tricystica, C. cystonchnoides, andC. steganocoela bear certain features in common with C. pachycystata thatsuggest possible relationship, nevertheless C. pachycystata differs mater-ially from those forms. Another form, C. pseudarmata Brown 1926,differs regarding Its excretory bladder. C. leptosoina Browai 1926 has fivepenetration glands on each side. C. pandora Faust 1921 has four penetra-tion glands on each side also, but its rudimentary intestinal ceca differradically from those of C. pachycystata. (See footnote on page 72.)Cercaria tridena nov. sp.(Figs. 78-80)Snails collected at Baton Rouge, Louisiana, in April, 1932, andlater identified as Hellsoma lantum, were found infected with a smallxiphidiocercaria, whose structure has points in common with that of C.steganocoela, C. tricystica, and C. acantliocoela. However, its digestivesystem and salivary glands differ noticeably from those of the abovecercariae.The worm does not encyst after emerging from the snail but soonsettles to the bottom of the container where it crawls about for approx-NORTH AMERICAN CERCARIAE—MILLER 75imately twenty-four to thirty-six hours before dying. It is not a strongswimmer, but moves rather aimlessly through the water with its bodycontracted, and bent ventrally, while its tail lashes vigorously. Thetail is short as compared to the body when the worm is at rest, and itcontains lateral folds when contracted.When the oval body is contracted the region just anterior to theacetabulum is much wider than the region posterior to this organ.Therefore, all width measurements were made in this region. Theanterior end is often extended into a snout-like process when it iselongated, and at that time the length of the oral sucker is greater thanits width.When at rest the body is 0.196 mm. by 0.106 mm., but may vary from0.168 mm. by 0.129 mm. to 0.392 mm. by 56 ix. The tail varies in sizealso. When almost completely contracted it is only 33 /x. long and 7?) /xwide at its base, but it varies from 0.112 by 0.14 mm. to 0.252 mm. by26 ix. Thus the tail is slightly shorter than the body (Fig. 79).Tiny spines, much smaller than those of C. acanthocoela, are in theanterior region, particularly lateral to the oral sucker. They thin outposteriorly and become much smaller, so that in the region of the ace-tabulum they are contained entirely within the cuticula. From a point ashort distance back of the acetabulum to the posterior end of the body,no spines can be seen.The caudal pockets are very much reduced so that the lumen is al-most absent. Setae could not be found on the walls of these pockets.When contracted, the tail is very short, being only a fraction of thelength of the body. It is attached to the ventral side of the body, anda short distance in front of the posterior end of the body (Fig. 78).A narrow lumen extends through the tail, and ends distally in an en-largement a short distance in front of the distal end of the tail. Thislumen possesses irregular swellings throughout its course. When thebody is quiet or crawling along by means of its suckers, the tail beatsmuch of the time.The oral sucker is only slightly larger than the acetabulum. Whenslightly contracted it is 44 ft, long and 93 /x in width while the acetabulumis 52 /x long and 56 /a wide. When at rest the oral sucker is 61 /x longand 72 p. wide. At the same time the acetabulum is 59 p. long and 59 p.wide. Thus the oral sucker is slightly the larger. It bears a compara-tively small stylet which has the thickened ridge, or shoulder, at the baseof its narrowed anterior third. However, this ridge is less pronouncedthan in the majority of these forms. Its thickened walls extend back-wards on either side of the stylet, and end in the region of the murkybase which is a small area definitely differentiated from the rest of thestylet by the absence of a thickened wall or hollow center. The stylet is76 ILLINOIS BIOLOGICAL MONOGRAPHS20 jj. in length and 4 /x in width at its base. The acetabulum is aboutmidway between the oral sucker and the posterior end of the body. Itis 49 ft posterior to the oral sucker when the body is contracted and 0.104mm. when extended. It is also 52 ft in front of the posterior end whencontracted, and 0.117 mm. while the worm is extended.Posterior to the oral sucker is a very short prepharynx which isevident only when the worm is extended (Fig. y^)), a comparativelylarge pharynx measuring 23 ft in both length and width, an esophagusreaching about half-way to the acetabulum, and intestinal crura whichlie close to the lateral margins of the acetabulum when the worm iscontracted, but describe a broad arc when it is extended. They, as wellas the esophagus, are very slender, and in various regions consist of solidmasses of tissue. However, the posterior regions are, in all cases,hollow. These crura extend 52 ft posterior to the acetabulum, or forabout half the distance between it and the posterior end of the body.Ducts from the penetration glands pass forward to a point on eitherside of the anterior tip of the stylet and open to the exterior. Underpressure a thick liquid can be seen slowly exuding from these openings.Posteriorly the ducts possess many enlargements, apparently due to theirtwisting, and connect to the glands in the region anterior and lateral tothe acetabulum. Only three large glands could be seen on either side ofthe acetabulum, with occasional lobes occurring in one or more of them.Dark granular masses, of a murky gray color, extend along eitherside of the body from the posterior end to a point a little behind theoral sucker. These may be cystogenous glands. Other globular bodiesare scattered over the body, most of them being anterior to the acetabu-lum. They are lighter in color than the penetration glands, and havedefinite clear walls. Genital cell masses lie immediately anterior andposterior to the acetabulum and consist of elongated masses of smallspherical cells (Fig. 78).The excretory bladder extends forward from the excretorv porealmost to the acetabulum before dividing into lateral arms to form abroad Y. As it contracts this bladder may constrict at the anterior endof its stem ; the fluids of the arms flow together, and there then appearto be two separate vesicles, a caudal and an anterior one. When thebody is contracted these arms form an irregular transverse vesicle.However, I have never noticed the separated lateral bladders appear-ing as in C. acanihocoela and C. tricystica. A greatly twisted main col-lecting tubule divides lateral to the acetabulum and slightly behind it toform a posterior and an anterior secondary collecting tubule. Just anter-ior to the acetabulum the anterior tubule divides into two smallerbranches, but due to the glandular nature of the body it is impossible totrace the tubules of the excretory system further.NORTH AMERICAN CERCARIAE—MILLER 77The liver tissue of Helisoma lantum was literally replaced by animmense tangled mass of short, oblong sporocysts, with compact, smoothoutlines (Fig. 80) rather than irregular ones as is characteristic of thesporocysts of many other Cercariae Armatae. Some older sporocysts arelight gray in color but most of them are a brilliant orange. Many ofthese sporocysts contain encysted forms which will be described later.The sacs average 0.756 mm. in length and 0.14 mm. in width.In one of these sporocysts a large overgrown cercaria was foundmuch like the one found in the sporocyst of C. acantJiococIa. This in-dividual was tailless and had lost its stylet, but was filled with a greatmass of material resembling C3'Stogenous material which obscured mostof the structures in the body. Its bladder was greatly swollen withexcretory granules as is the bladder of the metacercariae, the digestivesystem was plainly visible with only slight pressure, and the worm movedslowly as does a metacercaria after being liberated from its cyst. Thisworm is 0.246 mm. long, when mediumly contracted, and 0.151 mm.wide. The oral sucker is 62 fx wide and 59 fi long while the acetabulumis only 49 fi long and 53 jx Avide. The acetabulum is about 65 /j. posteriorto the oral sucker and 72 jx anterior to the posterior end. These meas-urements may mean that this individual indicates a dual infection but Ido not believe the differences noted here warrant such a conclusion.As previously mentioned, this form encysts readily within the sporo-cyst and liver tissue of the host. However, many never encyst, as shownby the fact that the encysted forms are present in relatively small num-bers, in comparison with the immense number of cercariae that emerge.The cyst wall is a clear, transparent, tough substance ; and when thewall is broken, the worm begins to move about. Eight ducts openseparately, dorsal to the cavity of the oral sucker. A group of tiny, elon-gated, tube-like structures was noted here in the cercaria before itencysted, but because of their miiuite size these structures could not becarefully studied. Distinct spines are on the anterior portion of thebody, but become smaller posteriorly until, in the posterior region ofthe body, they cannot be seen. The excretory bladder is now a largesac-like structure filled Avith granules and the crura reach farther poster-iorly tlian they did in the unencysted form. The lateral bodies, possiblyvilelline follicles, present in the cercaria are now more pronounced, andmany large cells witli prominent nuclei are scattered through the body.Another form, the cercaria of Lissorchis fairporti described b}'Magath (1917), resembles C. tridcna superficially but cannot be mis-taken for it because of the difference in the salivary glands and excretorybladder. The structure of its stylet is also different. C. crcnata Faust1917 differs from C tridcna in the number and arrangement of its78 ILLINOIS BIOLOGICAL MONOGRAPHSsalivary glands, in the possession of two very unequal suckers, shorterdigestive ceca, and various other characters of less importance. CIcptosoma Brown 1926 has five mucin glands on each side of its body.IX. FURCOCERCOUS CERCARIAEDiscussion of the GroupThe first furcocercous cercaria described was that one given thename Vibrio malleus by Miiller in 1773. Cercaria vivax Sonsino 1892,one of the first to be described outside of Europe, was also one of thevery earliest to receive a detailed description (Looss, 1896). Liihe (1909)briefly described the furcocercous larvae in Germany and neighboringcountries but grouped two of these individuals with his Lophocercariaebecause they were monostomes. He described the furcocercous cercariaeas follows:Distome Cercarien mit langem, an seinem freicn Ende gegabelten Schwanze,in welchen der schlanke Korper nicht zuriickgezogen werden kann. Entwickelungmeist in sehr langgestreckten Sporocysten, welche (ob bei alien Arten?) selbstan-dig beweglich sind, nur bei einer Art angeblich in Redien.Liihe divided these forms on the basis of presence or absence of eye-spots. Lebour (1911) divided the British marine forms into two pri-mary groups on the basis of development in sporocysts or rediae. Cortdescribed the first form reported from North America, Cercaria douthittiCort 1914.Because of Leiper's work (1915) the schistosome cercariae wereseparated from other furcocercous forms by their lack of a pharynx,of pigmented eye-spots, and of a cuticular keel on the furcae, which areless than one-half as long as the tail stem. Cort (1917) divided severalof these forms into three groups on the basis of presence or absence ofpharynx and eye-spots but his scheme is too limited to allow the inclusionof all forms now known. Sewell (1922) gave the first complete surveyof all furcocercous cercariae but he separated out all monostome formssince he considered the presence or absence of an acetabulum to be ofprime importance here in a system of classification. However, McCoy(1928, 1929a) found that furcocercous monostomes may develop intoadult distomes.Faust (1924) divided these forms according to the excretory sys-tem's flame cell pattern because he believed it was a natural basis forsuch grouping. His belief that it is a common system carried overfrom the cercaria to the adult would seem to be refuted by ]\liller'sstatement (1926a) that flame cells of the cercaria might have poten-tialities for more rapid division such that the pattern of the adult wormcould not be predicted. This has been illustrated in other forms, forinstance, in the larval and adult Schistosoma japonicum.NORTH AMERICAN CERCARIAE—MILLER 79Miller (1926a) in his comprehensive studies on furcocercous larvaedivided all known forms into two main groups, the ApharyngealCercariae and the Pharyngeal Cercariae, which probably constitutenatural groups. Each of these were subdivided according to whetherthe individuals were brevifurcate or longifurcate and distomes ormonostomes.The species included in my studies will be listed in their properposition in Miller's scheme of classification.Apharyngeal Brevifurcate Distome CercariaeDefinitionAll furcocercous cercariae with no pharynx, with furcae which areusually less than one-half the tail-stem length and frequently sharplydelimited from the tail-stem and which have both a ventral and oral suck-er were placed in this group by INIiller (1926a). He defined the brevi-furcate larvae as follows:Furcae usually less than one-half the tail-stem length; frequently sharplydelimited from the tail-stem. Tail-stem diameter less than that of body; usuallyattached somewhat ventrally, sometimes decidedly so, such that a dorso-ventralmount is rare. Furcal fin-folds sometimes present. Body frequently very hyaline.Eye-spots may be present. Anterior organ a very highly modified oral sucker,with anterior thin-walled and posterior muscular portions ; head gland usuallypresent. Ventral sucker usually much smaller in diameter than anterior organ;very protrusible and often held protruded. Penetration glands very large; fre-quently divided into anterior coarsely granular and posterior finely granular cells.Penetration gland duct openings frequently capped by hollow piercing spines. Ex-cretory openings at tips of furcae. Never more than one pair of flame cells in prox-imal part of tail-stem. Tail-stem wall usually provided with powerful longitudinalmuscles. Caudal glands not conspicuous ; when present, are not arranged in pairsalong caudal excretory tube. Tail-stem and furcae usually spined ; no sensoryhairs. Furcae almost cylindrical in some larvae. Alimentary canal opens more orless ventrally as a capillary tube; ceca absent or at most very short.Miller (1926a) divided the apharyngeal brevifurcate distomes intoeight subgroups and designated them as Subgroup A, B. C, D, E, F, G,and H. He listed twenty-six such forms and I have found descriptionsof additional ones, namely, Cercaria syncytadcna Faust 1926 and Ccrcariaanomala Rao 1929.Cercaria ivardi Miller 1923(Figs. 81-87)During my studies of infected Helisoma trivolvis collected in an Ox-bow north of St. Joseph in June, 1932, a unique furcocercous larva wasdiscovered which was described and named by Miller in 1923, and laterdiscussed in his monograph on the furcocercous cercariae. Additionalinformation about this form may be of value.80 ILLINOIS BIOLOGICAL MONOGRAPHSTlie body is very thick so that usually it must be viewed from the sideunder the cover-slip, only rarely a dorsal or ventral view being obtainable.The body is hrmiped above the tail insertion (Fig. 81) as is also that ofCcrcaria (jigas Faust 1918. Spherical eye-spots are the most prominentfeatures of the worm. Large prominent backward-pointing spines coverthe anterior end of the worm, forming a thick crown over the front halfof the swollen anterior portion of the oral sucker (Fig. 86) and reach-ing posteriori}' for a distance of about 46 ^i.The body is broadly subquadrate at its posterior end, and narrowedanterior to the acetabulum. When the body is under medium pressuremy measurements are as follows: Body length, 0.35 mm. and greatestwidtli at the posterior end. 0.156 mm.; tail stem, 0.689 mm. long, 65 ju,wide at base, 85 p. wide at its middle; furcae, 0.247 mm. long and 52 /xwide near base. These measurements slightly exceed Miller's.The oral sucker is pyriform in shape (Fig. 86) with the posterior endsmaller. It is about 0.13 mm. long by 68 /x in width at its anterior endand 39 /x at its posterior end. The acetabulum protrudes prominentlyand is easil}' everted by slight pressure. Its inside is thickly coveredwith small spines and the entire body contains tiny spines, those nearerthe posterior end being embedded in the cuticula. The acetabulum ismuch smaller than the oral sucker, being onl}' 50 /x in diameter. It issituated at the end of about the anterior two-thirds of the body. Theesophagus extends ventrad and soon divides into the two intestinal crurawhich extend to the acetabulum (Fig. 81).The circular eye-spots consist of spherical pigment granules whichappear as a black mass in a cavity containing a transparent fluid. How-ever, when these granules are scattered by pressure they are seen to bebrownish in color. They are about 0.182 mm. posterior to the anteriorend and 78 /x anterior to the acetabulum. Each measures 26 /x in trans-verse diameter and 20 /<, in longitudinal diameter.Many glands and other tissue fill the entire body of this cercaria.Penetration ducts, each consisting of several distinct parts, which opennear the ventral border of the anterior margin of the oral sucker, emergefrom the sucker ventrally and connect with a mass of five glands on eachside of the body. They are clear in appearance and lie dorsal to theacetabulum in large jiart, immediately behind the intestinal crura. Alarge, irregular, granular mass lies just posterior to these glands andnearly fills the body space posterior to the acetabulum. This is theposterior mucin body formerly mentioned by Miller (1926a).Just anterior to the posterior mucin gland, between it and the ventralsucker, is a germinal cell-mass. Surrounding the posterior mucin glandand particularly numerous dorsally, are manj^ large gland-like cells, each\\ith a large nucleus. These may be cystogenous in character. AuthorsNORTH AMERICAN CERCARIAE—MILLER 81have used various designations for these bodies. The anterior regionof the body is entirely obHterated after treatment with neutral red, be-cause of these dark nuclei.When quiescent the tail stem is twice as long as the body but it maybe much longer than this when it is fully extended. The furcae, usuallycontracted, are a little shorter than the body. The stem is narrowedboth distally and proximally and is attached to the ventro-posterior mar-gin of the body. It is parallel with the longitudinal axis of the body.Muscle fibers are prominent and have been described by Miller (1923,1926a). The furcae are slightly shorter than the body when quiescentunder pressure but in this state they are always contracted so that thefurcal fin-folds become fluted. Two dorso-ventral fin-folds extend alongeach furca throughout its length (Fig. 83) and possess numerous ray orrib-like structures, which are prominent at the end of the fin-fold (Fig.82).The study of the excretory system proved to be difficult since thissystem is obscured by the glands and other cells of the body. Two giantflame cells near the base of the tail stem constitute the most prominentfeature of the tail. Measurements which include the basal or nucleatedportion of the flame cells show it to be about 20 /a long while the flameitself is only 13 fi long. This vibratile portion becomes inactive whengreat pressure is applied and can then be studied in some detail. Evencamera lucida drawings can be made during this stage (Fig. 87). Thevibratile portion is clearly striated but there is no indication of therebeing separate cilia here. Four distinct dark bands, run longitudinallyand three narrow, lighter striations separate them from each other. Inmotion this structure resembles the undulating movements of a vibratilemembrane. The complete excretory system was determined (Fig. 84)and corresponds to the description given by Miller (1926a).When the snail was dissected the liver tissue seemed to be a living-mass of cercariae for the walls of the sporocysts are so thin, delicate, andtransparent that they are very easily broken. I have never disentangled acomplete sporocyst, but in a few cases have found parts of tlie sacs Avhichcontained maturing germ balls and cercariae (Fig. 85).Miller placed this form in his Group E of apharyngeal brevifurcatedistomes since all members of this group are unique in possessing aposterior mucin gland.Cercaria pteractinota E. L. Miller 1935(Figs. 88-93)Specimens of Physa gyrina collected at Twin Lakes near Paris, Illi-nois, and at Baton Rouge, Louisiana, were found to be infected with a82 ILLINOIS BIOLOGICAL MONOGRAPHSlarge brevifurcate form; those of Helisoma trivolvis, collected at CampCreek at Seymour, and at the Oxbow Lakes at Urbana and St. Joseph,were also infected with this cercaria. It hangs in the water with its headdownward when not disturbed but can move rapidly forward by its tailmovements. It has exceptional ability to extend itself, and the anteriorend is sometimes drawn out to form a narrow neck, extending by an out-pushing process which is probably due to the ability of the anteriororgan itself to extend. Under the cover-slip the long tail is a hindranceto locomotion by the suckers. The worm can live in tap water for along time, having been observed in the water for a period of thirty-onehours, at the end of which several of the worms were still living.The body is quite rectangular in shape, being wider at the posteriorend than at the anterior, when even slightly contracted. It is long andcomparatively narrow and may appear quite ribbon-like when completelyextended (Fig. 92). The tail is nearly three times as long as the bodywhen it is extended. The quiescent body is 0.27 mm. in length, and 0.363mm. long when extended. The widest portion, just posterior to the eye-spots, is 0.104 mm. The tail stem is 0.532 mm. long and 56 jx wide, andthe furcae are 0.185 mm. long and 28 /x wide at their bases.An immense number of tiny spines covers the body but those over theanterior half of the oral sucker, or anterior organ, are much moreprominent (Fig. 91 ). They are arranged in longitudinal and transverserows but spaced so as to make diagonal rows as well.The eye-spots are prominent features of the cercaria and are elongatedtransversely. They lie midway between the oral sucker and the smallacetabulum. When the worm is at rest they lie 96 /x posterior to theanterior end, and when it is extended, about 0.156 mm. posterior, and0.195 mm. from the posterior end. The two conspicuous black spots arelarge in comparison with the size of the body, being in width about one-third that of the body in that region. An eye-spot is about 39 ft in widthand 12 jx in length. A small compact mass of pigment, which resemblesthe eye-spot of a planarian worm, lies in the center of each pigmentmass. .Two other prominent pigment masses are present, one on eitherside of the oral sucker near its posterior end. Other scattered brownishmasses of pigment are distributed over the body, several of them beingconstant in position (Fig. 91).When the worm is at rest, the distance from the base of the tailto its bifurcation may be nearly three times as great as the length of thebody. A sharp division separates the tail stem from the furcae. Thesefurcae bear fin-folds on both sides of the distal one-half to two-thirdsof their length and each fold has numerous rays or ribs throughout itslength (Fig. 90). A broad central lumen runs longitudinally throughNORTH AMERICAN CERCARIAE—MILLER 83the tail stem, extending also into the furcae, and is evident when littlepressure is applied. The tail is inserted on the ventral side of the bodyand makes a noticeable angle with the long axis of the body because ofthis insertion. A membrane passes ventrally over the base of the tail,making a cup into which the tail fits. Longitudinal muscles run in adiagonal direction in the tail, both outer and deeper fibers being present.Two giant flame cells, very prominent, are in the basal portion of thetail stem.The digestive system leads posteriad from the elongated oral sucker,no pharynx or prepharynx being present. The oral sucker is much largerthan the ventral, measuring about 91 /x in length by 59 /x in width, whilethe diameter of the acetabulum is only 29 /x. The oral sucker is sub-terminal and fills the whole anterior tip of the body (Fig. 93). Thesmall acetabulum is on the tip of a prominent knob and is circular, easilyeverted with pressure, has its inner surface covered with spines, and hasa three-cornered opening. It lies 65 fi posterior to the oral sucker andabout 0.124 mm. anterior to the posterior end of the body. The esophagusruns posteriad and ventrad but it could be traced in the living specimenfor only a very short distance. It turns downward and runs ventrad tothe two eye-spots, along the body wall.Large ducts, tripartite in their anterior regions, pass posteriad over theoral sucker and extend ventral to the eye-spots, passing to a point slight-ly posterior to the acetabulum, where they communicate with the pene-tration glands. These glands fill a large portion of the body posteriorto the acetabulum. They occupy the dorsal regions of the body, aregranular, and distinguish themselves easily from the large lighter gland-ular bodies which fill most of the remaining space posterior to the eye-spots. However, under pressure these glands seem to fill the ventralregions posterior to the acetabulum.Two or three ventral compact masses of dark cells lie posterior to theacetabulum in the ventral region of the body. Two medium-sized com-pact bodies also lie just above the acetabulum. These bodies probablyrepresent the germinal masses of the cercaria. The anterior regions ofthe body are filled with tiny nuclei.The excretory bladder is almost forked by an anterior mesial pro-jection which incompletely divides it. The lateral main collecting tubulesdescribe an elongated loop (Fig. 88) and then divide into anterior andposterior collecting tubules. A large median excretory tubule runsthrough the tail to its fork where the tubule also divides, one fork runninginto each of the furcae and extending to the very tip where it ends in aslight enlargement. Two giant flame cells are situated a short distancedistal to the base of the tail, each connecting proximally with a tin}'collecting tubule which runs through the base of the tail into the body.84 ILLINOIS BIOLOGICAL MONOGRAPHSThe sporocyst of this form is a thin-walled, filiform sac. The walls ofthese sacs are so delicate that the separation of a single complete speci-men from the tangled mass of the liver tissue of the host is extremelydifficult. The walls are thin and easily broken so that it is not unusualto see the tail or body of an immature cercaria protruding through abreak in the wall. The dark pigment granules sometimes give the wallsa light grayish appearance but in most cases they are quite transparent.The sporocyst is so narrow that rarely more than a single cercaria lieslengthwise in the central cavity (Fig. 89). Several large cercariae andgerm balls were found in the sacs in various stages of development.The powerful tail is usually coiled lengthwise in the sporocyst. The im-mature forms lack pigment except for the two large eye-spots posteriorto the oral sucker.Several of these forms were found encysted in the liver of the snailsbut in all cases the worm inside was dead. Undoubtedly this is not anormal procedure. Attempts to recover encysted forms of C. pteractin-ota from crayfish were not successful.C. pteractinota belongs to Miller's group of apharyngeal brevifurcatedistome cercariae. The relatively few penetration glands and the ab-sence of eye-spots in all members of Group A prevents me from placingthis form there, while Group B also is characterized by only a few ofthese glands, only five pairs. The small size and presence of a few pene-tration glands in members of Group C also separate them from thisform. C. pteractinota lacks the posterior mucin gland of Group E, de-scribed above for C. wardi. The five distinct penetration glands and theposterior cell mass in members of Group G prevent me from listing C.pteractinota wdth these forms. C. elephantis Cort 1917 has a body andtail covered with spines and C. echinocauda O'Roke 1917 develops inrediae. Cercaria gigas Faust 1918 of Group H, has a much shorter tailstem, has flutings in the furcae instead of rays, has two distinct types ofglands, lacks the pigment masses described for C. pteractinota, and hasonly a single germinal mass of cells. C. pteractinota must therefore beplaced in Group F since it lacks the so-called posterior mucin gland andthe head gland found in Group E. The possession of numerous pigmentmasses, of numerous penetration glands, of two germ masses instead ofone, and of elongated sporocysts, instead of small oval ones, separatesthis new species from Cercaria indica xxxvi Sewell 1922, the only rep-resentative of Group F. More recent apharyngeal brevifurcate distomessuch as C. anomala Rao 1929 and C. syncytadcna Faust 1926 bear onlya superficial resemblance to C. pteractinota.NORTH AMERICAN CERCARIAE—MILLER 85Cerearia gigas Faust 1918(Fig. 94)This form was found only once in Pliysa gyrina collected in theSangamon River near Mahomet, Illinois, on May 29, 1932. FormerlyFaust (1918) reported this in Helisoma trivolvis and Physa gyrina fromDeKalb, Mt. Morris, and Urbana, Illinois. Few additions to Faust's ori-ginal description can be made since the snail host soon died after it wasbrought into the laboratory. The large, characteristic, pigmented eye-spots lying at a point about one-third of the body length from the anter-ior end (Fig. 94), the absence of a pharynx, the presence of a small,spined, protruding acetabulum, the long tail stem with very short furcae,the snout-like, elongate oral sucker which is also covered with spines, thegland cells posterior to the acetabulum, and the large number of pene-tration glands all help to identify this form as the sole member of GroupH of Miller's apharyngeal brevifurcate distome furcocercous cercariae.Pharyngeal Longifurcate Monostome CercariaeDefinitionAbout one-half of the furcocercous forms possess pharyngealsphincters. Miller (1926a) separated the longifurcate from the brevi-furcate cercariae on the basis of the following description:Furcae longer than one-half the tail-stem, sometimes exceeding it ; usually notsharply delimited. Tail-stem diameter approximately equal to that o£ body whenfully extended ; attached terminally, dorso-ventral mount the usual one. Furcalfin-folds absent. Body usually crowded with small parenchyme cells. Eye-spotsusually absent. Anterior organ less highly modified ; cells which possibly representa head gland present in but a few larvae. Ventral sucker frequently large, in somecases of greater diameter than anterior organ. Penetration glands small in pro-portion to body ; no differentiation into anterior and posterior sets. Usuallycoarsely granular, and acidophilic in sections. Solid piercing spines more frequentthan hollow ones. Excretory openings typically mid-furcal. Usually two pairs oftail-stem flame cells, seldom confined to a strictly proximal location. Tail-stemwall frequently annulated ; tail less powerful and more transparent. Conspicuous,more or less regularly paired caudal glands in a number of species. Tail-stemusually devoid of spines; furcae may be spined; sensory hairs on the tail-stems ofseveral larvae. Furcae never cylindrical, usually much flattened. Alimentary canalusually opens terminally or subterminally ; esophagus a fair-sized tube; ceca usuallywell-developed, frequently reaching almost to posterior end of body.Miller also divided the pharyngeal longifurcate monostomes intothree groups, the Vivax Group, the Tetis Group, and the RhabdocaecaGroup, and listed eight species as belonging to the three groups. Sincethen other forms have been described, namely, Cercaria dorsocandaTubangui 1928, Cercaria bessiae Cort & Brooks 1928, and Cercariaphysae Cort & Brooks 1928. The character of its excretory system indi-cates that C. dorsocauda undoubtedly belongs in the Vivax Group. C.86 ILLINOIS BIOLOGICAL MONOGRAPHSbcssiac and C. pJiysae belong to the Rhabdocaeca Group because they con-tain six posterior penetration glands instead of the numerous anteriorones characteristic of the Vivax and Tetis Groups. They also agree withother members of this group in possessing sensory hairs on the tail steminstead of spines, and in having an excretory system slightly different butstill characteristic of the group.The following forms have been placed in the Rhabdocaeca Group:1. Ccrcaria rJiahdocaeca Faust 1919 4. C. dorsocauda Tubangui 19282. C. hamata Miller 1923 5. C. bessiae Cort and Brooks 19283. C. iimltiicllulata Miller 1923 6. C. physae Cort and Brooks 1928Study of C. Jiamata and C. multicellulata, collected in Illinois, and ofC. bessiae, collected in Louisiana, has been made. Also descriptionsof two new species of these pharyngeal longifurcate monostomes will begiven here, one species from Illinois and the other from Louisiana.Cercaria Jiamata Miller 1923(Figs. 95-98)This cercaria was found in Helisoma trivolvis collected in the OxbowLakes near Urbana and St. Joseph, and in F. gyrina hildrethiana in LakeDecatur near Decatur, Illinois. IVIiller (1926a) reported it from the(Jrbana area. The worm lies in the water with its anterior end bentventrally, giving the hook-shaped appearance characteristic of so many ofthese forms. Annulations appear as the worm contracts slightly butthey are confined largely to the anterior one-half or three-fourths of thebody surface. In locomotion the tail functions so that the cercaria swimsbackwards by jerky spasmodic movements.Normally the stem and furcae are of about the same length, the bodybeing slightly shorter. The width of the tail stem is equal to that ofthe body unless the body is greatly contracted. Under pressure the bodyis 0.224 mm. long, the tail stem 0.252 mm. long, and the furcae 0.235mm. long. The body is 45 /x wide at its greatest width, the tail stem is39 p. and the furcae 28 /x at their bases. However, average measure-ments for slightly extended specimens are: body 0.151 mm. long, tailstem 0.213 mm. long, and furcae 0.209 mm. long. Spines are presenton the anterior tip of the body but do not extend much posterior to theregion of the oral sucker.An elongate, relatively large, terminal oral sucker empties into a verynarrow, undeveloped prepharynx and tiny bulbular pharynx (Fig. 95).The anterior organ is not pyriform as it is in C. nudticellulata. Theshort rhabdocoele gut represents the development of the digestive systembeyond the pharynx. The oral sucker is 29 jx long and 33 /.i wide whencontracted and 39 jx by 23 jx when extended. No acetabulum is presentbut a circular mass of cells which separates the anterior pair of penetra-NORTH AMERICAN CERCARIAE—MILLER %7tion glands from the two posterior pairs may be the undeveloped sucker.The pharynx is 12 /a in width and 9 /x in length while the prepharynx isabout 12 jx long.A group of six large clear nucleated penetration glands lies in theposterior region of the body. The three glands of each side are arrangedin linear fashion and taper into the narrow ducts leading from each.When the body is contracted these glands become globular or evenbroadly rectangular with the transverse dimension greater than thelongitudinal, but with body extension they become duct-like in appear-ance. A single clear vesicular nucleus is in the center of each gland.Each duct divides just in front of the anterior pair of glands, one ductpassing to the anterior gland and the other dividing to connect with thetwo posterior glands (Fig. 95). Anteriorly the ducts continue to theoral sucker and pass through it, where they become greatly swollen andthe two parts of the duct become distinctly separated. They open at theanterior end where they are associated with large, definitely pointedspines. For some distance posterior to the pharynx these ducts are in-distinct in the network of glandular bodies and tissue there.A mass of deeply-staining cells in neutral red, the germinal mass, isposterior to the penetration glands and anterior to the excretory bladder.Many small round nuclei are scattered over the body.A small, constricted excretory bladder lies at the posterior end ofthe body; it is constricted near its middle so as to give the appearance ofa double bladder. Extending posteriorly from this bladder is a singlemedian tubule which runs along the longitudinal axis of the tail-stemand divides near the fork (Fig. 98). A small island of Cort is present.Each branch of this tubule extends through one-half the distance of thefurca before ending in a solid rod of cells near its lateral border. I havenever seen external openings for these tubules as described by Miller, buthave seen a terminal solid mass there in some specimens. Anteriorly eachof the main collecting tubules of the body divides into an anterior and pos-terior branch. The anterior ends in four capillaries, each with its flamecell, and the branches of the posterior end in six flame cells, four ofwhich are in the body and two in the tail-stem (Fig. 95).The tail-stem is attached terminally as in C. multicellulata. It bearsnumerous sensory hairs which number about fifteen or sixteen oneach side (Fig. 96). Numerous caudal glands are present which be-come greatly flattened and distended under pressure. A wide, glandularlumen extends through this stem and divides to extend into the tips ofthe furcae. Many nuclei lie in the tail, both in the stem and furcae,and, from a surface view, are evenly distributed. Loose muscle bandsextend throughout the length of the tail-stem and terminate in the furcae.The furcae are very long, each as long as the tail-stem and longer88 ILLINOIS BIOLOGICAL MONOGRAPHSthan the body when at rest (Fig. 98). No fin-fold is present. Fromfour to six striations extend longitudinally through the furcae, the sixdistal striations decreasing in number near the basal region, until, at theproximal end, there are only four such lines. These striations do notoccur in the tail-stem. They are easily seen in the living, unstainedspecimen after strong pressure has been used but cannot be seen instained forms since the furcal nuclei obscure them. Two rod-like struc-tures (Fig. 97) arise at the posterior border of the furcal union andpass through about half the length of the furcae before ending nearthe outer margin of the furcae in a tiny mass of solid tissue. Occasion-ally one of these passes to the inner margin instead of to the outer.Earlier in this study they were believed to be the furcal excretory tubulesbut their apparent permanence under pressure makes me believe theyrepresent different structures.Great masses of slender, thread-like parthenitae fill all available spacewithin the outer membranes of the liver of the host. The sporocysts areattenuate structures and resemble a mass of slowly oscillating algael:)ecause of their power of independent movement. They can contract andextend and when contracted, swollen, bulb-like areas are present. Theyvary in color from orange to brown and contain developing larvae andloose tissue in their centers. Each is swollen at one end, and is unusuallyactive in its movements, its tip contracting much as the anterior end of anadult trematode. These bodies vary greatly in size. Narrow portions ofthe sac are only 28 jti in width while the swollen active ends are 84 ju, inwidth. The sporocyst averages about 56 ft in width and varies in lengthfrom 2.0 mm. to 9.73 mm. Many of the smaller ones are 3.5 mm. long.The birth pore mentioned by Miller was not observed.C. hamata differs from C. multicellulata and C. physae in that it lacksthe pigmented eye-spots which the latter forms have. C. bessiae has un-pigmented eye-spots and also has no caudal bodies. No pharynx hasbeen described for C. multicellulata. The possession of a well-developeddigestive system, of a different excretory system, and of a radically differ-ent body outline dift'erentiates C. dorsocauda from this form. C. rhah-docaeca lacks glands and sensory hairs on the tail-stem. Its bladder isvery different from that of C. hamata and it has no island of Cort. Theoval anterior organ, the tail-stem of uniform width, the limited bodyspines, the caudal bodies and sensory hairs, the island of Cort and bodyproportions all enable one to recognize C. hamata.Cercaria midticellidata Miller 1923(Fig. 99)The Physa gyrina hUdrcthiana found to be infected with this cercariaNORTH AMERICAN CERCARIAE—MILLER 89were collected at Seymour, Illinois, in Camp Creek, in April, 1932.Miller (1926a) reported it from Urbana, Illinois.The cercaria hangs in the water with its furcae above and open. Itmay dash suddenly through the water with the furcae working so asto draw the body after them. The body is shorter than the tail-stemand the furcae, but not noticeably so. The tail-stem is slightly longerthan the furcae when they are quiescent. Small, thickly-set spines coverthe anterior end of the oral sucker but thin out rapidly posteriorly,reaching only to a point about midway between the anterior organ andthe eye-spots. These small, pigmented eye-spots are about midway be-tween the oral sucker and the posterior end of the body.The tail is attached terminally and its stem and furcae are filled withmany large nuclei. Caudal bodies or glands are also present in the stem(Fig. 99) and are much more easily seen in some individuals than inothers, depending on the age of each particular cercaria. Small, narrowfin-folds extend along the sides of the furcae.No trace of a pharynx or alimentary canal is evident. The largeoral sucker is terminal and easily evertible, this action being repeatedcontinually under observation.The yellow, thread-like sporocysts were so tangled that individualswere not completely separated for study. Many parts of sporocystswere studied and found to be filled with germ balls and undevelopedcercariae in different stages of development.The pyriform oral sucker, the extent of the spination, the two pig-mented eye-spots, the uniform tail-stem, the thin fureal edges, thesensory hairs of the stem, the absence of a digestive canal or pharynx,the paired caudal bodies, the excretory system, and the mass of cellswhich separates the anterior pair of penetration glands from the twoposterior pairs, which may be the rudimentary ventral sucker, all helpto distinguish this form.The absence of a pharynx separates this from other pharyngeal longi-furcate monostomes. It also differs from all except C. hessiae and C.physae in the possession of eye-spots. Those of C. bessiae are not pig-mented. C. physae has only five pairs of caudal bodies while C. niulti-cdlulata usually has about eight pairs.Cercaria hessiae Cort & Brooks 1928(Figs. 100-101)The material which furnished the basis for the present study ofthis species was found at Baton Rouge, Louisiana, in April, 1932, inHelisoma lantum. Cort and Brooks have reported it from DouglasLake, Michigan, from Helisoiiia trivolvis.90 ILLINOIS BIOLOGICAL MONOGRAPHSThe cercaria hangs fairly motionless, head downward in the waterfor rather long intervals ; then the furcae suddenly flip rapidly and theworm shoots upward in the water, the tail foremost. When at rest thebody is characteristically bent downward like a hook, as mentioned byCort and Brooks.The body is elongated, with a round, narrow anterior end and sub-quadrate posterior end. Under slight pressure and when quiescent thebody is no wider than the tail-stem. When at jest the body is usuallyslighth' shorter than the tail-stem and furcae, while they are of aboutthe same length. When neither extending nor contracting under thecover-slip the body measures 0.168 mm. by 40 /j., the tail-stem from 0.196mm. to 0.241 mm. by 45 /x, and the furcae 0.185 mm. by 22 ju, at theirbases. When the body has the same width as that of the tail stem due toextension it is about 0.224 mm. long.Under high power a group of thickly-set spines can be distinguishedat the anterior tip of the body but they thin out rapidly posteriorly, notextending beyond the anterior third of the body. Annulations, due tothe contraction of circular muscles, are present on the anterior portionof the body. Two unpigmented eye-spots are located just anterior tothe first pair of penetration glands (Fig. 100).The tail-stem has a nuclear core which extends through its longitudinalaxis and also into the furcae. This stem is inserted in the body termi-nally, it lacks caudal bodies but has from six to ten sensory hairs on eachside. Surface nuclei are also present in the stem, and a single focus indi-cates that they are distributed regularly along either side of the stem,and through most of the furcae. Fine striations extend from the bases tothe tips of the furcae of the tail; six rows or lines commonly are present.The oval anterior organ is 33 /j, by 20 fi ; it is followed by a shortprepharynx, a small bulbular pharynx about 10 fx long, and a shortrhabdocoele intestine. A group of minute cells which separates the twoanterior penetration glands from the four posterior, is interpreted as therudimentary acetabulum.The genital primordium at the posterior end of the body just anteriorto the excretory bladder consists of a large mass of compact, deeply-staining cells in neutral red.The two penetration ducts open at the anterior end in close associationwith the numerous spines mentioned previously. Each duct is bipartite,is swollen in its course through the anterior organ, and extends posteriadto connect with the penetration glands. Near the posterior edge of theoral sucker these ducts decrease noticeably in size, but increase in theirposterior regions again where they lie close together, near the medianplane of the body, when the worm is not subjected to pressure. WhenNORTH AMERICAN CERCARIAE—MILLER 91pressure is applied they are pressed some distance apart and define a wavyregular course. There are three penetration glands on each side in theposterior region of the body. One-half of each mucin duct connects withtwo posterior glands, running under the anterior gland, while the otherhalf of the duct connects with the anterior gland. The large, clearnuclei are numerous in the body of the living worm.The bladder has a lateral constriction so that it is partially di-vided into a small posterior and a large anterior part. Lateral collectingtubules divide to form a posterior and an anterior secondary tubule nearthe anterior penetration gland and branch in the manner described by Cortand Brooks (1928). I have not succeeded in determining the connectionsof the third pair of flame cells because of the parenchyma which obscuresthis region.Cort and Brooks did not describe the sporocyst of this form. Theliver tissue of Helisoma lantum is filled with very long, narrow partheni-tae (Fig. 101) which occupy all available space. Few developing formsare in the central cavities but granular material is profuse. Brown andorange pigments give these sacs their characteristic color, which is of adeeper brown in the swollen parts of the sac. The ends are swollen andthe outline of the entire sporocyst is irregular, due to swollen areas alter-nating with constricted neck-like regions. It is very difficult to removea single complete sporocyst from the tangled mass in the liver of thehost. The narrowest width observed in the sporocyst was 28 /a, theaverage width was about 56 [x, and the width of the swollen end was0.112 mm. The largest forms are 5.6 mm. in length.This is the only species of the pharyngeal longifurcate monostomeforms which has unpigmented eye-spots. Other differences between thesespecies which prove to be of value in separating C. bessiae are: Thepossession of caudal bodies by C. Jianiata, C. multicelliilata, and C.physae ; the spines over all the body and tail of C. dorsocauda; the ab-sence of a pharynx in C. nmlticelhdata; and the different excretory sys-tem and large island of Cort in C. rhahdocacca.Cercaria furcalincata nov. sp.(Figs. 102-104)Helisoma lantum collected at Baton Rouge, Louisiana, in April, 1932,were found to be infected with a pharyngeal longifurcate monostomecercaria different from all those of this group previously described.It hangs in the water in a manner similar to that described for C.hcssiac, and its anterior end is bent downward to form a characteristichook (Fig. 103). Its method of locomotion is similar to that of C.hcssiac.92 ILLINOIS BIOLOGICAL MONOGRAPHSThe bod}' is not greater in width than the tail-stem when at rest orextended. When at rest the body is about 0.168 mm. long by 39 /ithrough its greatest width, the tail stem is 0.28 mm. long and 39 ft wide,and the furcae are 0.252 mm. long and 22 /x wide at their bases. Whencontracted the body is 0.101 mm. long and 56 /a wide. Under strongpressure with the body only slightly contracted it is 0.111 mm. by 72 p.,the tail stem is 0.247 mm. by 42 p., and the furcae are 0.247 mm. by 26 /x.These measurements indicate that the body is shorter than the tail-stemor the furcae, and that the stem and furcae are of about the same length.Spines are present at the anterior end but were not seen in theregions posterior to the oral sucker.The tail is attached to the ventro-posterior tip of the body. The stemand furcae contain a great number of scattered nuclei which are mostabundant in the lumen and along their sides. Five or six striations ex-tend lengthwise through the furcae and resemble those which I havepreviously described for other pharyngeal longifurcate monostomes (Fig.104). These broken lines have not been mentioned by other workers. Iknow of no function which they might perform except possibly that ofgiving rigidity to the furcae. They do not extend above the base of thefurcae. A single, broken, linear-like rod extends outward from each sideof the fureal union and ends near the outer wall of the furca. Theterminations vary in different individuals and may be occasionally on theinner wall of the furcae (Fig. 103). Possibly these rods also give rigidityto the furcae. They dift'er from those described for C. Jiamata whichwere continuous. Several pairs of large, elongated, irregular bodies liein the tail-stem on either side of the central excretory tubule which runsalong the dorsal side of the tail-stem. Ordinarily two pairs of theseglands are readily seen but in a few cases a third pair was noticed whichwas nearer the base of the stem. The sides of the stem are thrown intotiny irregular folds when the tail is slightly contracted, due to the circularmuscle fibers in this region. Bundles of longitudinal fibers extendthrough the stem and into the furcae.The oral sucker is elongated and oval in shape and measures 26 fx inlength by 16 ft, in width. Its narrow cavity opens into a sliort prepharynxwhich connects with a small bulbular pharynx. No other part of thedigestive tract was observed.A group of six penetration glands lies in the posterior half of thebody but further anterior to the bladder than those of C. hamata and C.midticellulata. These glands are smaller and more easily broken underpressure than those of C. bessiae and similar forms, and cannot be de-tected easily even with the use of neutral red, since the entire body isliterally packed with tiny, irregular or spherical nuclei which obscure allNORTH AMERICAN CERCARIAE—MILLER 93structures in the body. Only the regions immediately lateral and posteriorto the oral sucker are free from these nuclei. They make it very difficultto study the penetration glands and to determine their connections withtheir ducts. The glands dififer from those of related forms in that thoseof a pair are usually not directly opposite but may be shifted anteriorlyor posteriorly from such a position (Fig. 102). The ducts are bipartiteand define a wavy course to the oral sucker. They narrow noticeablyjust before entering this organ, then swell to several times that of theposterior diameter. Each duct finally separates into two distinct partsjust before opening at the anterior end of the worm in the region of agroup of long spines.A genital mass of small cells is just posterior to the penetrationglands. When the bladder has emptied, two large globular cells can beseen in the posterior end of the body. Each contains a very largevesicular nucleus. Their function is unknown. No primordium of theacetabulum is evident.The small excretory bladder has a lateral constriction which dividesit into anterior and posterior parts. A caudal tubule extends along themedian dorsal side of the tail and ends at a point exactly between thetwo furcae at the posterior margin. No branches have ever been seen inthe furcae of the tail. The excretory pore opens on the dorsal sidenear the posterior end of the animal. The bladder gives rise to two maincollecting tubules, each of which divides lateral to the anterior penetrationglands. A posterior branch extends into the tail but flame cells were notseen in the stem. The anterior collecting tubule soon divides into two,the median one soon dividing again into two, an outer and an innerbranch. The inner branch redivides and its mesial branch extendsacross the body and meets that from the opposite side to form a broadconnecting loop just anterior to the mucin glands. The excretory sys-tem of this form differs in this respect from other members of thisgroup but I am certain of the existence of this loop even though theterminal capillaries and cells of the excretory system were not traced.This cercaria differs from all other described pharyngeal longifurcatemonostomes in its possession of mucin glands of very indistinct character,small size, and uncertain position ; an excretory system with at least onelarge anastomosing loop; the presence of two large globular cells near itsposterior border ; very numerous, closely packed body nuclei ; and theexistence near its furcal union of two discontinuous or broken rod-likestructures differing from the solid ones of C. hamata. It also lacks theeye-spots of C. physae, C. bessiac, and C. multicellulata, the numerousbody and tail spines of C. dorsocauda, the larger penetration glandsof C. hamata, and the island of Cort of C. rhabdocaeca.94 ILLINOIS BIOLOGICAL MONOGRAPHSApiiaryngeal Longifurcate Monostome CercariaeDefinition of the GroupA discussion of the apiiaryngeal brevi furcate tlistonies has been givenpreviously. Those of the present group dififer in having the furcaelonger than one-half the tail-stem length, and in other features mentionedin Miller's description of the longifurcate forms. These forms have noventral sucker.Miller (1926a) found only one such form described in the literatureup to that time, namely Cercaria indica xxvii Sewell 1922. One otherform has more recently been described, C. scivelli Faust 1926.During the present studies a member of this subgroup was found inPhysa gyrina which was collected at liaton Rouge, Louisiana, in 1932.Morphological studies on this form enabled me to designate it as a newspecies in an earlier paper.Cercaria louisiana E. L. Miller 1935(Figs. 105-108)Physa gyrina collected near Baton Rouge, Louisiana, in June, 1932,harbored an apharyngeal longifurcate monostome which I have designatedas Cercaria louisiana. The worm is very active in the water, and whenin contact with a substratum, turns its ventral side downward (Fig. 108).For this reason it is nearly alwa3^s observed under the microscope with itsdorsal side uppermost. The body contracts and extends slowly but thetail-stem has less power to do so. The hook shape, seen from side viewand mentioned for many pharyngeal longifurcate monostomes, was notnoticed for this form.When well extended the body is as narrow as the tail-stem, withthe exception of the very posterior end. The anterior end is bluntlyrounded and bears on its surface a crown of large, narrow spines seeneasily under low power. They reach posteriad for not cjuite one-thirdof the length of the oral sucker (Fig. 105). As the worm contractslarge annulations appear which reach posteriad for about two-thirds ofthe body's length.The body normall}- is a little shorter than the tail-stem, and the tail-stem and furcae are of about the same length. Lender slight pressurethe body is 0.168 mm. long, the tail-stem 0.224 mm., and the furcae0.224 mm. At the same time the body is 43 ii wide, the tail-stem is 33 /a,and the furcae are 17 ^a at their base. The stem does not taper at itsdistal end. Under great pressure the body is 0.196 mm. long but the tail-stem and furcae still measure 0.224 mm. in length. The body of theworm is slightly prolonged ventrally and this projection fits into theNORTH AMERICAN CERCARIAE—MILLER 95tail's attachment (Fig. 105). A dorsal projection of the body covers thetail's attachment.No caudal bodies are in the tail-stem. However, many nuclei are inboth the stem and furcae (Fig. 106), and extending through the center ofthe tail is a broad band of muscle fibers. The band splits into two partsat the distal end of the stem and each part passes into a furca, reachingto its distal extremity. Also a horizontal band of fibers connects onefurca with the other and fuses with the other band in each furca (Fig.107). A narrow fin-fold is present on each furca. The delicate stria-tions so commonly observed in the furcae of the pharyngeal forms arealso present in this form, but the lines are less distinct, being more brokenand fused than in other forms.The terminal opening of the anterior organ opens into a narrowcavity lying between the swollen penetration ducts and extending throughthe sucker. No other part of the digestive tract was observed. Thelarge, elongated, oval, oral sucker is about 59 /x long and 29 jx wide. Noacetabulum is present but a packed group of small cells which lies betweenand slightly posterior to the two anterior penetration glands may repre-sent the undeveloped ventral sucker.Two dorsal, pigmented eye-spots are just in front of the anteriorpenetration glands. Each is a small, circular, compact body but pressurecauses it to separate into a number of pigment masses. The eye-spotsare ventral to the penetration ducts.Six large penetration glands lie in the posterior region of the body,the anterior pair being just behind the small eye-spots. Their ducts ex-tend forward as bipartite structures, the median half of each duct beingfilled with coarser granular material than that of the outer part of theduct. In the region of the oral sucker the ducts become very voluminousbut narrow again just before opening on either side of the mouth open-ing near the dorsal side of the body. The inner part of each duct con-nects with an anterior gland while the outer part divides into two ductseach connecting with one of the two posterior glands.Posterior to the penetration glands is a large mass of cells, thegerminal primordium. Many deeply-staining nuclei cover tlie bo(l3^'sstructures as they do the stem and furcae, but they are particularlydense in some regions of the body.The lateral constrictions of the small excretory bladder are not pro-nounced. The excretory system was not studied further because thehosts did not live long enough to enable me to do so.C. louisiana differs from C. iiidica xxvii in lacking the rhabdocoelegut and the numerous penetration glands of C. indica xxvii. Also theeye-spots of C. indica xxvii are non-pigmented, and its furcae are with-out the folds described for C. louisiana. C. sczvelli dififers from the abovespecies in possessing a dorsal body keel, eye-spots with pigmented96 ILLINOIS BIOLOGICAL MONOGRAPHScenters and only two pairs of penetration glands. Both C. furcalineataand C. bessiac differ from C. louisiana in lacking the furcal fin-foldswhich it has.X. CERCARIAEAHistory and DefinitionThis name was first used by Diesing (1855) as a collective groupname and not as a true generic name, for a group of little known larvaltrematode forms. Liihe (1909) defined the group as "Distomenlarven,bei welchen die Ausbildung eines Schwanzes iiberhaupt unterbleibt," andseparated it into the two larval genera Cercariaeum s. str., and Leucoch-loridium.Carus (1835) created the genus Leucochloridium to contain a speciesof larval trematode which he named Leucochloridium paradoxum, whichZeller found later developed into the adult Distomum macrostomum.Since Carus' description of the first Leucochloridium from Succineaamphibia on an island in the Elbe, several of these larval forms have beendescribed. However, Leucochloridium larvae have probably been discov-ered three times in North America up to this time. Call (1898) in speak-ing of Succinea obliqua in Indiana said, "the tentacles are rather large andthick, club-shaped, and are often the home of a stage in the developmentof a planarian." Ward (1918) states that Bryant Walker, in a personalletter, reported finding the larval stage of a Leucochloridium in Suc-cinea ovalis in Michigan. Magath (1920) reported a larval form fromFairport, Iowa, and gave it the name Leucochloridium problematicum.He reported it from both Succinea retusa and Planorbis trivolvis. L.assaniense was reported by Sewell (1922) from India, and L. millsi byFaust (1924) from China. L. cercatus has also been described by Mon-ticelli.The recent discovery by Mcintosh (1927, 1932), in Michigan, of adultLeucochloridium has added significance in connection with the followingsecond detailed report of the larval form from North America.Leucochloridium problematicum Magath 1920(Figs. 16-19)On October 8, 1931, I collected two Succinea ovalis Say from smartweeds, above the water at Cole's Pond, Charleston, Illinois, and uponopening one of them I found a large capsule-like object in one of thetentacles which proved to be the large branch of a sporocyst inside thebody of the snail. Tlie proximal end is very narrow while the distal halfNORTH AMERICAN CERCARIAE—MILLER 97of the sporocyst is banded with deep golden or brownish-red bands,varying in hue from almost yellow to brown and reddish-brown.This larva is remarkably like the one described by Magath (1920) atFairport, Iowa, and which he called Leucochloridium prohlematicum.This larva also resembles the one first described by Carus (1835) whichhe named L. paradoxum. Of course the possibility arises that perhapsthe green-banded sporocyst of Carus and the brown-banded ones whichMagath and I have reported are one and the same larva. Later workmay throw light on this subject. This sporocyst is about 12 mm. long inthe living condition and tapers into a thin thread at its proximal end,while the distal end is narrowly rounded (Fig. 17). The wall of thesporocyst is very tough.Small larvae could be seen inside the body. It is circled by reddish-brown bands at its distal end, there being four of them. Proximally thebands grow lighter, fading to a yellowish color, until, about midway be-tween the two ends, two broad, reddish-brown bands again occur, beingperhaps more brownish in color than the distal ones. Faint yellowishspots were also noted near the proximal end of the sporocyst. The colorvaries somewhat from that shown by Magath (1920) for L. prohlemati-cum; also the size is greater. However, it is very likely that his measure-ments were taken from preserved specimens while mine were made fromthe living worm. Nevertheless, the preserved sporocyst measured 6.0 mm.in length, which is still greater than Alagath's measurements.This sporocyst contained 147 small larvae, each enclosed in a rela-tively large, two-layered, transparent sac (Fig. 18), with the two suckersseparated from the rest of the sac at their openings by a bulb-like, thin,transparent membrane (Fig. 19). The larvae twist about in their sacs,and in doing so they move the sacs about as though they were parts of thelarvae's bodies. These sacs are about 1.37 mm. in length and about 0.823mm. in width through their acetabular regions. The measurements weremade from living worms without subjecting them to pressure. Somecysts are elongated and of a brownish color, some smaller and round andof a clear transparent color. The sporocyst was opened at 9:30 p.m. onthe 13th of October and the larvae within were placed in salt solution. Allof the cysts had partly dissolved by 11:00 a.m. on the 14th. The cystsabout the worms which I fixed in warm Gilson's fluid also disintegrated.The larvae are oval in shape, rounded at the anterior and narrower atthe posterior end. When well extended they measure about 1.206 mm.in length and when contracted, about 0.767 mm. in length and 0.514 mm.in greatest width, taken through the region between the pharynx andacetabulum.98 ILLINOIS BIOLOGICAL MONOGRAPHSThe oral sucker and acetabulum are large in proportion to the size ofthis tiny worm, the acetabulum lying near the anterior margin of theposterior third of the body. However, in the preserved specimen this issomewhat different, with the acetabulum at the anterior half of the body,as described by Magath. The suckers are both powerful, more so thanthey are pictured by Magath. The oral sucker is 0.297 mm. in lengthand 0.322 mm. in width when contracted, and about 0.3 mm. in lengthand 0.2 mm. in width when extended. It is situated about 56 /a posteriorto the anterior end of the body when the body is extended. A very briefesophagus is evident when the worm is greatly extended ; however, in thecontracted, preserved individuals this cannot be seen. The pharynx inthe living specimen is only slightly wider than long but in the preservedspecimen measures 57 /i long and 0.124 mm. wide. In the living animalit is about 0.15 mm. long and 0.10 mm. wide when the body is extended.There is no prepharynx.The two intestinal crura extend, in a wide arc, almost to the posteriorend of the body (Fig. 16). In a contracted or preserved specimen theydefine a broad curve as they extend posteriad. The distance from theacetabulum to the posterior extremity of the body is about 0.277 mm.The large acetabulum is 0.24 mm. in diameter. It lies about 0.25 mm.back of the posterior end of the oral sucker, its anterior margin not reach-ing to the middle of the body. As mentioned previously, this position isgreatly altered by preservation. The posterior ends of the ceca areslightly pointed and the thickened walls extend throughout their length.The excretory bladder is relatively very small in proportion to the sizeof the worm and lies close to the posterior extremity of the body. Itextends diagonally in a postero-dorsal direction where it opens throughthe excretory pore which is close to the posterior extremity of the body.Two powerful siphons extend anteriad, and lateral to the ceca to a pointlateral to the oral sucker, then turn posteriad and at a point just an-terior to the bladder divide into several secondary branches. The largestbranch extends anteriad, giving ofif branches in its course, until it endsas a single fine collecting tubule lateral to the oral sucker. Each capillaryends in a flame cell but because of the intricate network of vessels andflame cells (Fig. 16) it was impossible to be certain of the connectionsof all parts of this complicated excretory system. Material on hand waslimited.The genital organs are well developed in these larvae; the two testes,the ovary, the rounded organ, and cirrus sac that Magath (1920) men-tions for L. prohlematicum are all readily identified. The genital openingis on the dorsal side of the body and posterior to the reproductive organs.It is near the posterior extremity of the body, even posterior to the ex-cretory pore.NORTH AMERICAN CERCARIAE—MILLER 99The locations of these reproductive glands vary in the preserved andmounted specimens. It should be noted that the testes are described hereas elongate ovals rather than spheres, as they have been pictured in draw-ings of L. problematicum and L. paradoximi. Measurements of theseorgans in preserved specimens were taken. The anterior testis is to theright of the midline and is 67 /x long; the left posterior testis is 57 //,long; the spherical ovary is on the left side of the body and is 52 jx longand 48 /x wide ; the elongated cirrus sac tapers anteriorly and is 76 /x by48 IX ; the so-called round body, lies between the two testes, and it is 48 fxin diameter.In spite of several differences between these forms under discussion,I shall not designate this form as a new species, since work is being con-tinued regarding its life history and morphology. With the present evi-dence, I am inclined to refer to it as only the first report of Leucochlori-dium problematicum from Illinois, and the second report from NorthAmerica.XI. SUMMARY1. The larval trematode fauna of areas of Illinois, Louisiana, andFlorida has been studied.2. Nineteen previously described species from Illinois, Iowa, Michi-gan, Louisiana, Florida, and Wisconsin have been studied.3. Four new species have been added to the list of North Americanforms, one from Florida, two from Louisiana, and one from both Illinoisand Louisiana.4. All descriptions were made from the living animal under uniformconditions.5. Each species has been placed in its proper group, the history anddefinitions for each group having been previously given.6. The twenty-three larvae are one Cercariaeum, two Gorgoderines,one Monostome, one Echinostome, one Cercaria Ornata, three CercariaeMicrocotylae, six Cercariae Armatae, three Apharyngeal BrevifurcateDistome Furcocercous Cercariae, four Pharyngeal Longifurcate DistomeFurcocercous Cercariae, and one Apharyngeal Longifurcate MonostomeFurcocercous Cercaria.7. Several new hosts and many new localities were found for previ-ously described cercariae.8. Complete infection records for all forms have been correlated intables.9. An identification key for all described Illinois larval trematodes hasbeen prepared.10. The relative merits of various morphological features of the larvafor diagnostic value have been discussed.100 ILLINOIS BIOLOGICAL MONOGRAPHSBIBLIOGRAPHYBeaver, P. C.1929. Studies on the Development of Allassostoma parvuin Stunkard. Jour,Parasit., 16:13-23; 1 pi., 5 text-figs.Braun, M._1891. tJber die Freischwimmenden Sporocysten. Zool. Anz., 14 : 368-369,Brown, F. J.1926. Some Freshwater Larval Trematodes with Contributions to their LifeHistories. Parasitol., 18:21-34; 3 pi.Call, R. E.1898. A Descriptive Illustrated Catalogue of the Mollusca of Indiana. Reportof the State Biologist, Indianapolis.Carus.1835. Beobachtung fiber einen merkwiidigen schongefarbten, etc. Nova ActaAcad. Caes. Leop. Carol. Natur. Curios., 17:85-100.Cawston, F. G.1921. Some South African Cercariae. South African Jour. Nat. Hist., 3:199-204; 1 pi.1921. South African Larval Trematodes and their Intermediary Hosts. Trans.Amer. Micr. Soc, 11:119-130.Chatterji, R. C.1933. 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Ueber Redien und Sporocysten Filippi. Arch. Anat. Physiol., u. wissensch.Med., 145-150; 6 pi.Ward, H. B.1916. Notes on Two Free-living Larval Trematodes from North America.Jour. Parasit., 3:10-20; 1 pi.Ward, H. B., and Whipple, G. C.1918. Fresh-water Biology. Chap. XIII, "Parasitic Flatworms." New York,nil pp.Wesenberg-Lund, C.1931. Contributions to the Development of the Trematoda Digenea. I. TheBiology of Leucochloridium paradoxum. Det. Kgl. Danske. Viden-skabernes Selskabs. Skrifter., Raekke 9:90-142; 6 pi., 7 text-figs.Willey, C. H.1930. A Cystophorous Cercaria, C. projecta n. sp. from the Snail, Helisomaantrosa, North America. Parasitol., 22:481-489; 5 text-figs.WUNDER, W.1924. Bau, Entwicklung und Funktion des Cercarienschwanzes. Zool. Jahrb.,(Anat.), 46:303-342; 19 text-figs.NORTH AMERICAN CERCARIAE—MILLER 105EXPLANATION OF PLATESUnless otherwise stated, all drawings were made from living ma-terial under pressure of the cover-slip, with the aid of a camera lucida.Outlines, and in most cases, the suckers, were drawn with camera lucidaand the remaining structures inserted free-hand. In all cases the pene-tration elands were drawn after neutral red had been added.Abbreviationso anterior (penetra-tion) organac anterior cell massav anterior vesicleb folded bodybp birth porec covering cells ofbladderca capillarycb caudal bodycc cyst cavityeg cystogenous glandcl caudal lumenen caudal nucleusep constrictionepo caudal pocketcs cirrus sacet globe cavityd duct of penetrationglandse encysted individualeb excretory bladdereg excretory granules/ fin-foldfr fureal raysfro furcal rodfs furcal striationsg gelatinous cystgb germ ballgc germ cell-massi island of Cort/ longitudinal musclesIv lateral vesicleme main collectingtubule)iie median eye-spotovarype pigmented eye-spotpg penetration glandpi posterior locomotorappendagepin posterior mucin bodypv posterior vesiclerb round body.y swollen ridgesc secondary collectingtubulesh sensory hairssin sphincter musclet testistf tail foldstg tail globett thread of tailve vesicular cell106 ILLINOIS BIOLOGICAL MONOGRAPHSPLATE INote.—Fig. 8 is semi-diagrammatic ; the scale for Fig. 6 represents 0.01 mm.;scales for Figs. 1, 2, 5, 13, and 14 represent 0.05 mm. ; scales for all other figuresrepresent 0.1 mm.Figs. 1-9.—Cercaria sphaerocercaFig. 1.—Ventral view, digestive system shown in broken lines to denote positionin body; suckers semi-diagrammatic.Fig. 2.—Structure of tail globe under pressure.Fig. 3.—-Encysted worm in proximal cavity of tail globe.Fig. 4.—Entire tail appendage showing three distinct parts.Fig. 5.—Side view showing prominence of ventral sucker.Fig. 6.—Side view of stylet showing its dorsal hump.Fig. 7.—Distribution of nuclei in distal portion of tail as revealed by neutral red.Fig. 8.—Various shapes assumed by the bladder during life ; semi-diagrammatic.Fig. 9.—Sporocyst showing undeveloped body on tail globe within.Figs. 10-15.—Cercaria mitocercaFig. 10.—Ventral view of body showing main features.Fig. 11.—Ventral view showing spherical cell-like bodies after collapse of excretorybladder under pressure.Fig. 12.—Tail appendage showing three definite divisions.Fig. 13.—Proximal vesicle of tail globe showing thick walls.Fig. 14.-—Surface of tail globe during contraction showing fissures.Fig. 15.—Sporocyst showing typical shape.NORTH AMERICAN CERCARIAE—MILLER 107PLATE I108 ILLINOIS BIOLOGICAL MONOGRAPHSPLATE IINote.—Figs. 19, 31, and 32 are semi-diagrammatic drawings; scales for allother figures represent 0.1 mm.Figs. 16-19.—Leucochloridium problematicumFig. 16.—Ventral view, showing principle branches of excretory system.Fig. 17.—Banded sporocyst from the snail's tentical.Fig. 18.—Body together with gelatinous sheath surrounding it, while subjected tostrong pressure.Fig. 19.—Side view of same showing connections of suckers to outside.Figs. 20-27.—Cercaria urbanensisFig. 20.—Dorsal view, showing main structures of body.Fig. 21.—Early stage of encystment immediately after loss of the tail.Fig. 22.—Much later stage of encystment still showing region of tail attachment.Fig. 23.—The worm about forty-eight hours after encystment.Fig. 24.—Redia showing complete digestive cecum.Fig. 25.^Characteristic shape of old redia.Fig. 26.—Young redia with cercariae in various stages of development.Fig. 27.—Cercaria in an early stage of development ; taken from redia.Figs. 28-32.—Cercaria trivolvisFig. 28.—Dorsal view of the worm with excretory tubules and cystogenous glandsshown on alternate sides.Fig. 29.—Mature redia showing digestive cecum and birth pore.Fig. 30.^—Redia showing posterior locomotor appendages and anterior collar.Fig. 31.—End of tail showing the small distal body only partially invaginaled;semi-diagrammatic.Fig. 32.—End of tail showing the distal body protruding completely; semi-dia-grammatic.NORTH AMERICAN CERCARIAE—MILLER 109PLATE II110 ILLINOIS BIOLOGICAL MONOGRAPHSPLATE mNote.—Figs. v^4 and 48 are semi-diagrammatic drawings ; scales tor Figs. 39, 4.^,and 44 represent 0.01 mm. ; scales for Figs. 41, 42, 47, 49, and 52 represent 0.05mm.; scales for all other figures represent 0.1 mm.Figs. 33-34.—Cercaria trk'olvisFig. 2)2).—Redia showing posterior appendages and withdrawn anterior end.Fig. 34.—Nuclei of tail under very strong pressure.Figs. 35-40.—Cercaria iiiesofyplilaFig. 35.—Ventral view of body.Fig. 36.—Ventral view showing complete excretory system.Fig. 37.—Mass of sporocysts in the liver tissue.Fig. 38.—One end of a sporocyst enlarged to show cercariae within.Fig. 39.—Dorsal view of stylet, showing its globular base.Fig. 40.—Sagittal section showing germinal masses dorsal to acetabulum.Figs. 41-46. Cercaria cystorhysaFig. 41.—Ventral view of body; dorsally located st3det shown with solid outline;body contracted.-Ventral view showing main branches of excretory system; extended.-Dorsal view of stylet, showing lateral shoulders.-Tail under strong pressure and neutral red, showing nuclei and caudalhairs.-Sporocyst containing cercariae in various stages of development.-Mass of sporocysts attached to the liver tissue of the snail.Figs. 47-51. Cercaria meniscadena-Ventral view with principle structures shown.-Contracted tail show^ing lateral folds ; semi-diagrammatic.-Sporocj'st with developing cercariae.-Sporocyst showing characteristic knobs of older forms.-Sporocyst with more pronounced knob.Fig. 52. Cercaria cyclicaFig. 52.—Ventral view of the body showing penetration apparatus.Fig. 42.Fig. 43.Fig. 44.Fig. 45.Fig. 46.Fig. 47.Fig. 48.Fig. 49.Fig. 50.Fig. 51.NORTH AMERICAN CERCARIAE—MILLER 111PLATE III112 ILLINOIS BIOLOGICAL MONOGRAPHSPLATE IVNote.—Fig. 57 is a semi-diagrammatic drawing; scales for Figs. 56, 62, 63, and67 represent 0.01 mm.; scales for Figs. 55, 58, 61, 66, and 68 represent 0.1 mm.;scales for all other figures represent 0.05 mm.Fig. 53.—Cercaria cyclicaFiG. 53.—Ventral view showing main tubules of excretory S3'steni.Figs. 54-59.—Cercaria acanlhocoela-Ventral view of body.-Lateral view of body under no pressure.-Dorsal view of stylet showing lateral projections.-Various shapes assumed by excretory bladder during life; semi-dia-grammatic.-Sporocyst showing typical shape; cercariae and germ balls within.-Encysted individual showing distension of bladder by granules.Figs. 60-65. Cercaria tricystica-Dorsal view of body, with suckers shown in broken lines.-Ventral view with penetration ducts showing.-Dorsal view of stylet showing soft base.-Lateral view of same stylet. "-Tail treated with neutral red to show nuclei.-Sporocyst with typical elongate-oval shape.Figs. 66-68.—Cercaria cystonchnoidcs '-Contracted tail showing central lumen.-Dorsal view of stylet showing lateral swellings.-Lateral view of body when greatly extended during movement; verylittle pressure.Fig. 54.Fig. 55.Fig. 56.Fig. 57.Fig. 58.Fig. 59.Fig. 60.Fig. 61.Fig. 62.Fig. 63.Fig. 64.Fig. 65.Fig. 66.Fig. 67.Fig. 68.NORTH AMERICAN CERCARIAE—MILLER 113PLATE IV114 ILLINOIS BIOLOGICAL MONOGRAPHSPLATE VNote.—Scales of Figs. 72 and 76 represent 0.01 mm. ; scales for Figs. 71 and 74represent 0.05 mm.; scales for all other figures represent 0.1 mm.Figs. 69-70.—Cercaria cystonchnoidesFig. 69.—Dorsal view of body showing complete excretory system.Fig. 70.—Sporocyst showing typical terminal knobs.Figs. 71-73.—Cercaria steganocoelaFig. 71.—Dorsal view of body.Fig. 72.—View of stylet when turned slightly on its side.Fig. 73.—Drawing showing filiform sporocyst with various stages of cercariaewithin.Figs. 74-76. Cercaria pachycystataFig. 74.—Dorsal view of the body.Fig. 75.—Mass of sporocysts in the liver tissue.Fig. 76.—Top view of stylet, showing soft, globular base.NORTH AMERICAN CERCARIAE—MILLER 115PLATE V116 ILLINOIS BIOLOGICAL MONOGRAPHSPLATE VINote.—The scale for Fig. 87 represents 0.01 mm. ; scales for Figs. 79, 80, 82,85, and 88 represent 0.1 mm. ; scales for all other figures represent 0.05 mm.Fig. 77.—Cercaria pachycystataFig. 77.—Dorsal view of body to show branches of excretory system in posteriorregions of the body.Figs. 78-80.—Cercaria tridcnaFig. 78.—Dorsal view of the body.Fig. 79.—Lateral view of the body under no pressure.Fig. 80.—Sporocyst showing one encysted individual.Figs. 81-87.—Cercana zuardiFig. 81.—Lateral view of the body with the eye-spots flattened by pressure.Fig. 82.—Tail, showing fin-folds, striations in furcae, and caudal excretory tubule.Fig. 83.—Furca, showing rayed fin-folds in their dorsal and ventral positions.Fig. 84.—Lateral view of body, showing complete excretory system.Fig. 85.—Section of a sporocyst showing developing germ balls and cercariae.Fig. 86.—Anterior end of body showing dorsal view ; also showing spined crown,pyriform anterior organ, digestive tract, and eyes.Fig. 87.-—Greatly magnified view of a caudal flame cell immediately after move-ment has ceased, showing striations.Fig. 88.—Cercaria pteractinotaFig. 88.—Dorsal view of body showing eye-spots and the large branches of theexcretory system.NORTH AMERICAN CERCARIAE—MILLER 117PLATE VI1 18 ILLINOIS BIOLOGICAL MONOGRAPHSPLATE VIINote.—Fig. 94 after original by Faust; Fig. 99 after original by H. M. Miller;scales for Figs. 89, 92, and 98 represent 0.1 mm. ; scales for all other figures repre-sent 0.05 mm.Figs. 89-93.—Cercaria pteractinotaFig. 89.—Portion of sporocyst showing developing cercariae and germ balls.Fig. 90.—Furca, showing the rays of the fin-fold.Fig. 91.—Dorsal view of body showing eyes and the other six principle pigmentmasses ; other pigment not shown. Also the pyriform sucker andcrown of spines are shown.Fig. 92.—Dorsal view showing the entire cercaria.Fig. 93.—Lateral view to show position of numerous penetration glands and thegerminal masses.Fig. 94.—Cercaria gigasFig. 94.—Dorsal view of cercaria; after original of Faust; X 125Figs. 95-98.—Cercaria hainataFig. 95.—Dorsal view of body, showing penetration glands, germ masses, digestivetract and complete excretory system.Fig. 96.—Tail-stem showing sensory hairs and caudal bodies.Fig. 97.—Furca showing central lumen and small furcal rod.Fig. 98.—View of cercaria, showing relations of body, tail-stem, and furcae.Fig. 99.—Cercaria iiiulticelhilalaFig. 99.—Dorsal view ; after original of Miller ; X 500NORTH AMERICAN CERCARIAE—MILLER 119PLATE VII120 ILLINOIS BIOLOGICAL MONOGRAPHSPLATE VIIINote.—Fig. 100 after original by Cort and Brooks ; scales for Figs. 101, 103,and 108 represent 0.1 mm.; scales for all other figures represent 0.05 mm.Figs. 100-101.—Cercaria bessiaeFig. 100.—Dorsal view of Cercaria; after original of Cort and Brooks; semi-diagrammatic drawing.Fig. 101.—Section of filiform sporocyst.Figs. 102-104.—Cercaria furcalineataFig. 102.—Dorsal view of body and anterior portion of tail-stem.Fig. 103.—Entire cercaria without pressure, to show relation of body, tail-stem,and furcae.Fig. 104.—Enlarged furca showing furcal striations and position of nuclei.Figs. 105-108.—Cercaria louisianaFig. 105.—Dorsal view of body showing anterior crown of spines, oval anteriororgan, eye-spots, penetration glands, germinal mass, rudimentarysucker, and excretory bladder.Fig. 106.—Tail-stem, showing position of muscle bands and nuclei after neutralred has been added.Fig. 107.—Furca, showing fin-folds, nuclei, and position of muscle bands.Fig. 108.—Entire cercaria showing relations of body, tail-stem, and furcae; drawnwithout the application of pressure.NORTH AMERICAN CERCARIAE-MILLER 121PLATE VIIILfBRAHYOF THEINDEXActinonaias carinata, 15, 21, 22, 24, 33Ampullaria depressa, 15, 20, 22, 67, 68Anodonta fluviatilis, 33lacustris, 33Campeloma sp., 16, 21Cercaria A (Tsuchimochi), 41acanthocoela, 11, 14-16, 19-22, 24, 26,60, 62, 64-66, 69, 70, 71, 74-77, 112,113acanthostoma, 24, 26, 41agilis, 40, 41of Allassostoma parvum, 23, 25anchoroides, 28anomala, 79, 84arcuata, 41aurita, 23, 25, 37bessiae, 17, 20, 22, 86, 88, 89, 91-93, 96,120, 121biflagellata, 28brookoveri, 28brunnea,^ 52californieiisis, 27, 28calliostoniae, 28candelabra, 24, 26, 60, 71capsularis, 27, 28catenata, 41candadena, 41caiustoni, 71cellulosa, 52cephaladena, 71chekiensis, 41chisolenata, 24, 26, 41cliitinostoma, 41chlorotica, 52fiia, 41complexa, 24, 26, 41constricta, 41convoluta, 23coronata, 41crenata, 60, 77cribrata, 71cristacantha, 41cucumeriformis, 41O'c/iVa, 15, 20, 22, 57, 110-115cystonchnoides, 15, 20, 22, 67, 74, 112-115cystophora, 27, 28cystorhvsa, 18, 21, 22, 24, 25, 52, 54,110, 111dendritica, 60diaphana, 60, 64, 67diastroplia, 23, 25diiiiorpha, 71dorsocauda, 85, 86, 88, 91, 93douglasi, 11dotUhitti, n, 24, 26, 7Sduplicata, 33cchinata, 41echinatoidcs, 41echinocauda, 84of Echinoparyphium flexum, 41Echinostome species^ (Tsuchimochi),41Echinostome species J5 (Tsuchimochi),41of Echinostomum revolutuiii, 41of Echinostomum xenopi, 41elephaniis, 84ephemera, 37equispinosa, 41of Euparyphium murinnm, 41fulvoculata, 37furcalineata, 17, 20, 22, 91, 96, 120, 121fiisca, 28fusiformis, 41f//,9a^. 18, 21-24, 26, 80, 84, 85, 118, 119glandulosa, 60, 64, 67gorgoderae cygnoidis, 29gorgoderae loossi, 29, 31gorgoderae pagenstecheri, 29, 31gorgoderae varsoviensis, 29, 32granulosa, 41qregaria, 60/mwioia, 14, 15, 18-24, 26, 86, 88, 91-93,118, 119haskelli, 60hemilophura, 24, 25, 47, 50, 51hemispheroides, 37of Himasthla militaris, 40, 41hodgesiana, 28Jmmilis, 71hyalo Cauda, 37hypoderaei conoidei, 41imbricata, 36, 37indica xi, 37XII, 41XVII, 65, 67XX, 41XXIII, 41XXIV, 47XXVII, 94, 95XXVIII, 47XXXV, 27, 28XXXVI, 84XLi, 40, 41XLVIII, 41Lvii, 52infracaudata, 23, 25, 37ingracilis, 71inhabilis, 23invaginata, 28isidorae, 41isocotylca, 24, 25, 59, 60, 64, 66konadensis, 37laqueator, 28lebouri, 37leptosoma, 41, 72, 74, 78limnaeae ovatae, 71123124 ILLINOIS BIOLOGICAL MONOGRAPLISlimnicola, 41of Lissorchis fairporti, 60littorinae obtusatae, 41longistyla, 47louisiana, 19, 20, 22, 94-96, 120, 121(Glenocercaria) lucania, 36, 37macrocerca, 26, 29Diacrocercoides, 28tnacrosioiiia, 24, 26, 28Diacrura, 28viagnacauda, 41niegalura, 24, 25iiiehrai, 41melanophora, 28nieniscadena, 12, 13, 21, 22, 24, 25, 54,66, 110, 111mesotvphla, 11-14, 16-22, 24, 25, 47, 48,50, 51, 65, 74, 110, 111microcotyla, 52niicropharynx, 60microxiphifera, 71viinima, 24, 26mirahilis, 28mitocerca, 15, 21, 22, 24, 25, 29, 33, 106,107iiioiiosto})ii, 37multicellulata, 16, 20, 22-24, 26, 86, 88,89, 91-93, 118, 119nimiher 7 (Nakagawa), 41oniata, 46, 47pachycystata, 14, 18, 20, 22, 24, 25, 72(footnote), 74, 114, 116palustris, 41pandora, 74paracephalade)ia, 71patellae, 41pekinensis, 28pellucida, 27penthesilia, 41/'/ly^a^', 86, 88, 89, 91, 93plana, 27polyadena, 24, 25, 59, 60, 64, 66prima, 46, 47projecta, 28pseudariiiata, 71, 74pseudo-echinostoma, 41pseiidornata, 52pteractinota, 11-14, 18-22, 24, 26, 81, 84,116-119piirpurae, 41quissetensis, 41racemosa, A7rebstocki, 41redicystica, 41reflexae, 24, 26, 40, 41rhabdocaeca, 24, 26, 86, 88, 91, 93robusta, 23, 25, 26, 37robusticauda, 24Sagittarius, 27, 28secimda, 71senii-robusta, 41serp£ns, 41jezy^//i, 94, 95spatula, 23, 25, 37sphaerocerca, 15, 21, 22, 24, 25, 29, 30,33-35, 106, 107spinifera, 41splendens, 28steganocoela, 16, 17, 20-22, 24, 26, 69,71, 74, 114, 115stephanocauda, 28stilifera, 24, 25, 60stylobuc calls, 71syncytadena, 79, 84syringicaiida, 28tenuispina, 69, 71tetradena, 72trabeculata, 27tricystica, 19, 20, 22, 65-67, 74, 76, 112,113/r/Je;m, 17, 20, 22, 74, 77, 116, 117trifurcata, 24, 25, 47tn7o6fl, 69, 71triophthalmia, 27trisolenata, 41trivolvis, 11, 12, 14, 18-23, 26, 41, 42,44,45, 108, 111urbanensis, 14, 15, 20, 22, 23, 25, 36, 37,108, 109vaullegeardii, 27, 28z;iVa.t', 787yar£ft, 19, 21-24, 26, 79, 84, 116, 117zvrighti, 28yenchingensis, 27yoshidae, 28zostera, 27Cercariae, Amphistome, 7, 25Apharyngeal, 79Apharyngeal Brevifurcate Distome,79-85Apharyngeal Longifurcate Mono-stome, 94-96Armatae, 25, 46, 58-78Binoculate, 25, 37-39Cystocercous, 7, 24, 26-28Cystocercous, of Liihe, 26-35Cystophorous, 27, 28Distome, 7Echinostome, 23, 26, 40-45Furcocercous, 7, 24, 26, 78-96Gasterostome, 7Gorgoderinae, 24Gorgoderine, 25, 29-35Gorgonocephalous, 7Gymnocephalous, 24, 25Leptocercous, 7, 40Lophocercariae, 7IMacrocercous, 26Megalurous, 40jMicrocercous, 7Microcotylae, 25, 46, 51-58IMonostome, 7, 23, 25, 36-39Ornatae, 25, 46-51Pharyngeal, 79Pharyngeal Longifurcate Alonostome,85-93Polyadenous, 46Rhopalocercous, 7NORTH AMERICAN CERCARIAE—MILLER 125Trichocercous, 7Trioculate, 25, 2i7Virgulae, 46Xiphidiocercariae, 24, 46-78Cercariaea, 24, 26, 96-99Cleopatra bulmoides, 27Distomum inacrostomum, 96Eossaria ohrussa, 17, 21Glypthelmins qiiieta, 50Goniobasis livescens, 13, 18, 21-24, 52, 54pulchella, 23Goniobasis sp., 16, 21Gorgodera cygnoides, 29Helisoma lantum, 17, 19, 20, 22, 65, 6674, 77, 89, 91trivolvis, 11, 13-24, 42, 45, 72, 79, 8286, 89Leucochloridium assamcnse, 96cercatus, 96niillsi, 96paradoxum, 96, 97, 99prohleniaticum, 14, 20-24, 26, 96-99108, 109Lissorchis fairporti, 77Lymnaea reflexa, 24Lymnaea sp., 17, 21Musculium transversum, 15, 21, 22 2429Nassa obsoleta, 11Natica alderi, 27Notropis whipp Hi, 64Phvsa crandalli, 20gyrina, 11, 13, 14, 16-24, 42, 45, 48, 5081, 85, 94gyrina hildrethiana, 11, 13-17, 20-2224, Z7, 48, 60, 61, 86, 88halei, 11, 16, 20, 22, 24, 48Planorbis marginatiis, 27trivolvis, 96Pleiirocera acuta, 12, 13, 15, 21, 22, 24, 54elevatum, 24Schistosoma japonicum, 78Succinea amphibia, 96obliqua, 96ovalis, 14, 20, 22-24, 96retiisa, 96Trochus cinerarius, 27Vibrio malleus, 78Viviparous georgiana, 15, 20, 22, 57UNIVERSfTY OF ILLINOIS-URBANA3 0112 065097112

A New Megalura Cercaria from Ohio

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A New Megalura Cercaria from Ohio

Abstract

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