Electron-microscope studies have shown that the epicuticle of the hydropyle consists of 2 layers. The inner is complexly folded and the outer consists of a meshwork of fine fibrils which fills the spaces between the folds. The endocuticle is laminated, penetrated by pore canals, and contains many wax-canal filaments. The filaments are especially abundant immediately before diapause.
During diapause a dense, homogeneous layer is present at the outer surface of the hydropyle. It is absent before diapause and discontinuous or absent in eggs which are developing without diapause, or after diapause has been prevented or broken. The results confirm the conclusions, based on earlier studies, that the hydropyle is waterproofed by a waxy coating during diapause and that this material is absent or discontinuous in eggs which are developing.
The vitelline membrane is an excessively thin, dense layer which lies below the chorion and lines the micropyles. It is less resistant at the posterior end of the egg than elsewhere. During development it is incorporated into the cuticle, which is secreted by the serosa. It is now believed that the ‘resistant endochorion’ described earlier for this species is identical with the vitelline membrane which Salt described in 1952 for the eggs of Melanoplus bivittatus.