Structure of ovaries and formation of egg envelopes in the stonefly, Leuctra autumnalis Aubert, 1948 (Plecoptera: Leuctridae). Ultrastructural studies.

The investigation of ovaries and the formation of egg envelopes of the stonefly Leuctra autumnalis was carried out with light and transmission electron microscopes. The ovary of the studied species is paired and consists of several dozen panoistic ovarioles opening individually to the oviduct. The process of egg capsule formation already begins in previtellogenesis. At this time the follicular cells secrete precursors of the vitelline envelope. Analysis of the presented data suggests that the oocyte itself also takes part in the formation of the vitelline envelope during late vitellogenesis. Simultaneously, the follicular cells produce precursors of further layers of the egg capsule, i.e. two-layered chorion and extrachorion, consisting of two gelatinous layers and a flocculent one. The completely developed capsule contains channels, probably micropylar ones.