A fibrous layer on the surface of eggs of the parasitoid, Cardiochiles nigriceps (Hymenoptera: Braconidae), has been implicated by earlier studies in the evasion from encapsulation by host hemocytes. The present histochemical and ultrastructural study was undertaken to characterize fibrous layer material and to determine the source of fibrous layer and other components of the eggshell. The fibrous layer contains neutral glyco- or mucoprotein; acidic mucoproteins or glycosaminoglycans are absent. The mature eggshell is resolved into 5 morphologically distinct layers by electron microscopy: (from inner to outer) vitelline envelope, endochorion, an electron-dense "irregular layer", papillary layer and fibrous layer. During oogenesis each eggshell layer is laid down sequentially in the order mentioned above. Eggshell material appears to be produced by the follicle cells because these develop extensive rough endoplasmic reticulum and golgi apparatus and exhibit apparent exocytotic activity at the plasma membrane adjacent to the egg. none