Egg shell thickness patterns as shown by individual domestic hens

Synopsis

Shell thickness shows practically no variation around any one latitude, but a considerable variation from pole to pole. These so‐called patterns of shell thickness have been studied in a number of birds. It is evident that individual birds often show a fairly constant pattern of thickness over long periods of time, but that different birds have quite different patterns. Some birds show a gradually changing pattern with time. One bird sometimes laid two eggs on one day. The first egg of these two conformed to the normal pattern for that bird while the second egg showed a quite different pattern, which might be the normal pattern in reverse.