Printed in Great Britain THE EGG SHELL OF THE HOUSE CRICKET (ACHETA DOMESTICUS): AN ELECTRON- MICROSCOPE STUDY

Consecutive changes in two discrete layers of the egg shell of the house cricket, Acheta domesticus, have been claimed to control the uptake of water by the eggs. The development of the shell has been re-investigated with the electron microscope by examination of eggs at different stages of embryogenesis and of ovarioles containing oocytes at various stages of maturity. It is confirmed that fragmentation of the maternal epicuticle and deposition and resorption of the serosal cuticle are the only apparent changes in the shell during development. The exis-tence of a serosal epicuticle is confirmed and a distinction is made between the serosal epicuticle and the vitelline membrane. Previously unreported features of the shell are (i) an outer zone of the maternal endocuticle which seems to be the most stable part of the maternal cuticle, (ii) a microlaminar organization within the scales of the maternal epicuticle, (iii) a vitelline membrane containing specialized regions, which remains distinct from the serosal epicuticle throughout development, and (iv) the osmiophilic character of the serosal epicuticle, its complex fine structure and its origin. Observations on eggs which had just begun to absorb water allow us to suggest that fragmen-tation involves a shrinkage of the material of which the scales are composed