The Avian Egg: Water Vapor Conductance, Shell Thickness, and Functional Pore Area

Gas exchange in the avian embryo has been shown to be dependent on, and limited by, the diffusive properties of gases across the resistance offered by the shell and shell membranes ( Wangensteen and Rahn 1970-71). For simplicity, we shall use the term “shell’ to denote the entire barrier to diffusion between the interior of the egg and the environment. It has also been shown that under normal conditions the diffusion of water vapor across the egg shell approximates the diffusion equations set forth for ideal gases (Paganelli et al. 1971) and that the weight loss in eggs is almost entirely due to diffusion of water through the shell (Romanoff and Romanoff 1949). The diffusive rate of water loss from eggs is: