Oogenesis in Campodea sp. (Diplura): the ultrastructure of the egg chamber during vitellogenesis.

The egg chamber of Campodea consists of a group of nurse cells and an oocyte, and is surrounded by a simple, markedly flattened follicular epithelium. Three types of yolk occur in the oocytes: type I appears within elements of the rough endoplasmic reticulum; type II is produced by specific complexes of endoplasmic reticulum and dictyosomes; type III is incorporated by micropinocytosis. Histochemical tests show that mature yolk spheres contain proteins and polysaccharides. The main function of the nurse cells is to synthesize RNA, but they also produce small amounts of type I yolk. Phylogenetic conclusions are drawn from this and other studies of oogenesis in apterygote insects.