Spermatogenesis in the Hard-Shell Clam (Venus Mercenaria Linnaeus) *

Neither Kellogg7 nor Belding' in their papers on the biology of V. mercenaria give a description of spermatogenesis occurring in this animal, and until the present time the general features of this process in dams have not been described. In the case of some other lamellibranchiate mollusks, more information on the development of the gonad and gamete formation is available. Hoek' described the origin and growth of gonads in 0. edulis, but failed to give an accurate description of spermatogenesis. Orton9, while greatly contributing to our knowledge on sex change in 0. edulis, did not extend his studies into the sphere of gametogenetic activities. In discussing the development of gonads in 0. commercialis, Roughley'0 gives only a brief description of the proliferation of sex cells. Coe2 described in detail the spermatogenesis in the California oyster, 0. lurida, and later gave a brief account of the same process in 0. virgimica. The same author,4 describing sexual phases in Teredo, referred to spermatogenetic activities observed in that animal. Okada,8 studying gametogenesis in Musculium heterodont, mentions briefly the different stages of spermatogenesis, but does not give a complete account of it. Among the recent studies on spermatogenesis in Gastropods the work of Tuzet12 and of Furrow5 should be mentioned. The gonads of young V. mercenaria, developing sexual products for the first time, are lined with a layer of germinal epithelium composed of flattened, somewhat irregular cells containing large, deeply staining nuclei. Later when the germinal epithelium differentiates into larger cells indifferent gonia appear. Fig. 1 gives a diagrammatic picture of spermatogenesis in this species. In an early stage of gametogenesis it is exceedingly difficult, if not entirely impossible, to distinguish the ovogonia from spermatogonia because there appears to be no morphological differentiation existing, and the cells resemble each other very closely. Such cells are, as a rule, always found lying in contact with the inner surface of the follicular wall