Homology of Male Genital Sclerites in Cockroaches (Blattaria) by Means of Analysis of Their Association Patterns’

(1) Male genitalia of five species of the Blattaria, namely Periplanetu fuliginosa (Blattidae : Blattinae) ; Bhzttella spp. (germanica, kamyi, and subvittata) (Blattellidae : Blattellinae) ; and Opisthoplatia orientalis (Blaberidae : Epilamprinae) were examined. In addition, the drawings of Periplaneta americana figured by Crampton (1925), and those of Blatta orientalis by Snodgrass (1937) (both Blattinae) were referred to for the comparisons. The three subfamilies referred to above were considered to represent three variations of the genital structures: 1) strongly sclerotized, with the ventral outstanding lobe (= Blattinae type for the superfamily Blattoidea) ; 2) largely membranous, with the left retractable hook (= Blattellinae type for the family Blattellidae with a few exceptions) ; 3) largely membranous, with the right retractable hook and left retractable sclerites (= Epilamprinae type for the family Blaberidae). (2) The homology of membranous regions as well as sclerites were studied, assuming that the entire genital pouch could be divided into subregions (SRs) which correspond to the observed structures whenever sclerotic or not. It obviously dues to a great degree of replacement of sclerites with membrane that the Blattellinae type and Epilamprinae type are hardly relatable to the Blattinae type. (3) Eleven SRs are commonly recognized bilaterally throughout the examined species. They are grouped into the dorsal (D) and ventral (V) major regions in the genital pouch. D is divided into Dl, D2, and D3 ; V includes Vv and Vd as its components ; Dl includes Dld, Dlm. Dlv, Dlvm, and Dll ; in D2, there are D2d, D2v, and D21. D3, Vv, and Vd are not divided. (4) There are three kinds of neighboring relations (= associations) between SRs : association by fusion, by articulation, and by adjacency. Even when two sclerites are interrupted by a membrane, unless largely separated, a week adjacency between them is recognizable. They are applied in a plane graph of association pattern to show relationships of the entire SRs. (5) The association pattern of the sclerites (SRs) is introduced as a useful tool for identification of the genital sclerites. The pattern involves the rule of arrangement of the sclerites in the entire structural complex. Undoubtedly, it is more stable than the concrete form of the sclerites themselves. The graphs of association pattern in the different types are very similar, although they do not completely agree in detail. (6) Musculature is of less importance in the identification of the male genital sclerites, but is helpful only supplementally. The muscles among the various types studied are inconsistent in number and points of attachment on the sclerites. The almost exclusive reception of the sternal muscles on the rod-like structures observed in the middle in the Blattellinae and Epilamprinae types strengthens their identification with D3 or apodemal sclerites of the Blattinae type. (7) The outermost hook of the left phallomere of the Blattinae type and retractable hooks of the Blattellinae and Epilamprinae types, which often, had been suggested as homologous, are considered to be derived from different SRs’ and thus not to be homologous structures. (8) As suggested by Quadri (1940), the male genitalia of the Blattoidea is concluded as a paired structure. The current view that the genitalia of the Blattoidea (Blattinae type) is comprised of three principal lobes or phallomeres (Snodgrass, 1935) is rejected here. The outstanding ventral phallomere (the third phallomere) in the type is shown to be a ventral element of the right phallomere (RVv). On the other hand, the left ventral element (=LVv) of this type was retained as a small flattened sclerite set ventrally in the fasces of the left phallomere. (9) Three types of genitalia may have arisen independently from a symmetrical ancestral type. The Blattellidae and Epilamprinae types are almost mirror images of each others suggesting that there had existed symmetrical basic plan which had possessed potential to differentiate similar structures