Studies on egg shells. XVI.—variations in shell thickness over different parts of the same shell

Abstract

AbstractVariations in shell thickness over the surface of the egg have been studied in a number of normal and abnormally thin shells. There is far less variation around the latitudes of the egg than there is longitudinally. Different birds give, for normal shells, different patterns of thickness from pole to pole, but for any one bird the pattern is usually fairly constant. The most frequent general pattern is one in which the broad and narrow caps each have a thickness greater than most intermediate latitudes, but the minimum value may fall in different positions in different eggs.Abnormally thin shells seem to deviate from the normal pattern for the same bird, but it will be necessary to carry out more work on this before reliable conclusions can be drawn.With a collection of eggs, the thickness of one latitude is highly correlated with the thickness of another latitude and it is possible to calculate from assumed values for one latitude the pattern for the rest of the shell.Various methods for obtaining an accurate value for mean shell thickness by using a sample of measurements have been compared.