Eggshell porosity and the water metabolism of the chick embryo

Chick embryos have been water stressed during the last week of incubation by either withdrawing 6 cm 3 of allantoic fluid or by increasing shell porosity three to four fold. Despite the large increase in water loss from these eggs they were successfully incubated to produce hatchlings of apparently normal water content. The chicks produced by water deprivation were significantly smaller than controls and it appears that the growth of embryos is therefore modulated according to the metabolites available. If this interpretation is correct it suggests that the critical role of eggshell porosity in avian development has been over‐emphasized.