The hen's egg: Shell shape and size parameters and their interrelations

Abstract

Synopsis The occurrence of a crack in an egg shell depends in part on the local strength of the shell, which in turn depends on its curvatures as well as its thickness, and therefore on its shape. Selection for shell shape is therefore needed; but before the breeder can do this he must have a rapid and accurate method of quantifying shell shape, and knowledge of the factors that affect its variation. A procedure is described whereby nine measurements of an egg shell—length, maximum breadth, distance from the plane of maximum breadth to the broad pole and the distances by which each pole projects into annuli of diameters 1.5, 2.5 and 3.5 cm—are used to obtain an equation describing the profile of the egg in polar coordinates. It has five parameters that measure, independently, five shell characteristics: scale, aspect (breadth‐to‐length ratio), skewness, marilynia (concordant bulging between the poles and the plane of maximum breadth) and platycephaly (discordant bulging). Egg volume and superficial area c...