The Avian Egg: Surface Area, Volume, and Density

The surface area of the avian egg through which the developing embryo must exchange heat, metabolic gases, and water vapor is a variable of prime importance for quantitation of the permeability of the egg shell to these substances. Surface-area measurements are necessary if one is to compare the permeability properties of shells ranging in size from less than 0.5 g in hummingbirds, to 1.5 kg in the Ostrich (Struthio camelus), and to more than 10 kg in the extinct Aepyornis. In the course of experiments designed to measure and compare the water vapor permeability of eggs of many species (Ar et al. 1974), we found it necessary to develop a method of measuring surface area that was both convenient and accurate.