Fig. 1. (A) Schematic of an insect eggshell, drawn from published information on Manduca and Drosophila. Features are not to scale. From left to right, the layers are: chorion, trabecular layer (TL), crystalline chorionic layer (CCL), wax layer, vitelline envelope (VE), serosal cuticle (SC), serosal membrane (SM), serosa, embryo, yolk. From the VE outwards, all layers are in place at oviposition, having been secreted by maternal follicular cells. By contrast, the SC and SM are secreted from the serosa, which is derived from the blastoderm. The SC is secreted first, starting at about 12 h after oviposition (at 24°C), followed by the SM from 23–44 h after oviposition (Lamer and Dorn, 2001). The embryo develops closely apposed to the serosa (rather than deep within the yolk), both before and after katatrepsis. The yolk itself becomes cellularized in the first 12 h after oviposition (Lamer and Dorn, 2001). (B) Schematic of gas flux model. The model terms represent the characteristics of five different layers or sets of layers. From left to right they are: boundary layers around the egg or its substrate, chorion, trabecular layers, a combination of the CCL, wax layer and VE, and all remaining interior layers.