Electron microscopic study of the differentiation and development of trophocytes and oocytes in Gerris najas...

The differentiation of oogonia and oocytes, and of trophocytes, from undifferentiated germ line cells has been studied in Gerris najas, a pond skater, from the fourth instar to the adult animal. For the first time criteria have been obtained which allow the distinction between poorly differentiated early oogonia and nurse cells. The most important criteria are the size, shape, and structure of nuclei and mucleoli. This is consistent with the different function of these cell types, which is primarily a different nuclear function: meiosis in the oocytes, and RNA synthesis to support the trophic core and the oocytes in the trophocytes.