In Ephemeroptera, in spite of the absence of accessory glands in the female genitalia, the eggs frequently show adhesive coats. Ul trastructural observations of the female reproductive apparatus ofHabrophlebia eldaedemonstrated that the elaboration of chorionic adhesive layers takes place in ovarioles and oviducts. In ovarioles, follicle cells synthesize viscous material that is released on the chorionic surface, and that coalesces to form: a) electron‐dense masses closely packed on both sides of the ridges that characterize the fully formed chorion in this species; and b) a thin granular layer that covers the egg surface before ovulation. During passage through the oviducts, the chorion is enriched by products secreted by the cells delimiting the oviductal lumen.