Oxygen and water vapour conductance in the shell and shell membrane of the american crocodile egg

Abstract

1. 1. The water vapor conductance ( G H 2O ) of the egg of Crococdylus acutus was found to be 21.0mg H 2O day −1 torr −1 H 2O. This value is approximately twice that calculated for a bird egg of equivalent weight. Adaptation to a high humidity environment is suggested. 2. 2. The oxygen diffusion coefficients ( K o 2 ) were measured independently on samples of eggshell plus membrane and were found to be markedly dependent on the degree of hydration, ranging from a K o 2 of 1.2 × 10 −6 cm 3 STP-sec −1 cm −2-torr −1 for desiccated conditions to a K o, of 2.3 × 10 −7 cm 3 STP sec −1 cm −2 torr −1 for conditions of maximal humidity. The larger K o 2 values agree with those calculated from G H 2O data and suggest that water vapor and oxygen are both moving by gaseous diffusion along the same pathways. 3. 3. The individual contributions of the shell and of the membrane were determined. Under dry conditions membrane resistance was negligible but as hydration increased, the resistances of shell and membrane both increased markedly. 4. 4. In the nest environment the conditions determining shell and membrane hydration are likely to be critical factors governing rates of gas and water exchange.