ULTRASTRUCTURE OF THE VITELLOGENIC EGG CHAMBERS OF THE CADDISFLY BRACHYCENTRUS-INCANUS (INSECTA, TRICHOPTERA)

Ovarian structure and cellular composition of the oocyte and associate d cells in Brachycentrus incanus (Insecta: Trichoptera) were examined by light and transmission electron microscopy. The ovary consisted of numerous ovarioles, each containing at least one maturing oocyte with its associated nurse cells and follicle cells. The ooplasm consisted p rimarily of electron-dense yolk bodies and lipid droplets. An oocyte n ucleus was discernible only in pre- and early vitellogenic stages. Sev en nurse cells, at the distal end of each oocyte, were connected throu gh cytoplasmic bridges to the oocyte and to each other. Each large lob ate nurse cell nucleus contained uniformly spaced clumps of heterochro matin and numerous nuclear pores; the cytoplasm contained mitochondria , a small amount of non-dilated granular endoplasmic reticulum (GER), agranular vesicles, and numerous free ribosomes. Follicle cells, which formed a layer around the oocyte, each contained a large oval nucleus with abundant heterochromatin and a moderate number of nuclear pores; the cytoplasm contained abundant dilated GER, mitochondria, Golgi bod ies, and free ribosomes. Oocyte microvilli interdigitated with those o f the follicle cells through a filamentous extracellular material of v ariable electron density. This is the first detailed description of eg g chamber ultrastructure in this major insect order The overall struct ure is very similar to that of other neopterous insect orders, includi ng Lepidoptera, to which Trichoptera is generally considered to be clo sely related.