Electron microscopic study of follicle cell development during vitellogenesis in the marine crustacean Isopoda, Idotea balthica basteri.

The ultrastructure of follicle cells has been compared to that of developing oocytes in the marine crustacean isopod, Idotea balthica basteri, at different periods of the molting cycle. There was a distinct change in the shape and size of the follicles and in their relation to each other and to the oocytes. During stage 1 of vitellogenesis (molting cycle period C), spaces between the follicles appeared and enlarged. At the same time, the exogenous yolk fraction penetrated the oocytes, and villi, issuing from both the follicle cells and the oocytes, formed. Maximal follicle cell activity occurred during stge 2 of vitellogenesis (molting cycle period D) when micropinocytotic uptake stopped. This cellular activity was characterized by the synthesis of some granular material and the development of the rough endoplasmic reticulum and the Golgi vesicle. The granular material participated in the formation of the chorion. The follicle cells seemed to degenerate shortly before laying, and thus the follicular epithelium did not appear to be permanent in Idotea.