The electron microscopy and cytochemistry of oogenesis and the cytochemistry of embryonic development of the prosobranch gastropod Bembicium nanum L.

While some workers have studied cytochemical localizations during oogenesis in molluscs (e.g. Arvy, 1949, 1950; Bretschneider & Raven, 1951; Collier, 1960; Cowden, 1961; Pasteels & de Harven, 1963), others have examined the ultrastructure of the developing oocyte using the electron microscope (e.g. Rebhun, 1956a, b, 1961; Worley & Hershenov, 1960; Pasteels & de Harven, 1963). This work has been reviewed by Brachet (1960) and Raven (1961). In the present study of Bembicium nanum, both technical procedures have been employed, in an attempt to examine nuclear and nucleolar structure and interrelationships, nucleocytoplasmic relationships and changes in cytoplasmic complexity during oogenesis and vitellogenesis. Cytochemical localizations and their changing patterns during the embryonic development of molluscs have also been investigated by a number of workers, especially for the embryos of Limnaea, Physa and Aplysia, and reviewed by Raven (1958) and Hess (1962). With the exception of studies on Limnaea (Raven, 1958), this work is limited in scope and in no case ventures beyond the trochophore stage. The present work, therefore, also attempts a survey of cytochemical localizations throughout the development of B. nanum from the fertilized egg to the hatching veliger.