Intraspecific Variation in the Purple Secretion of the

cause of the red to purple fluid secreted from the margin of its mantle. There is only a superficial resemblance between this secretion and that of the genus Mttrex, which is the source of the anciently famous dye, "Tyrian" or "Royal Purple. " Aplysia purple, however, found no practical use, probably because of one important deficiency-it turns a dirty brown upon exposure to air and sunlight. Our knowledge of the nature and composi-tion of aplysia purple has been increased peri-odically since DeNegri (1876) presented a series of beautifully colored spectra. The most significant of the early papers is that of MacMunn (1899), who attempted an analy-sis but concluded that there was no reason to believe that aplysia purple was composed of more than a single component. Durrien and Turchini (1925) published a minor observa-tion which, unfortunately, was recognized as the oldest literature on the subject by some later authors. Schreiber (1932) presented the results of an extensive study of aplysia purple. He divided the purple into two components, one of which he showed to be a substance similar to urobilin and the other its precursor substance, which is also pigmented but very unstable. Fontaine and Raffy (1936) made suggestions as to the possible source of th