Deuterocoel Deutero- + Greek. Koilos Hollow)

The deuterocoel is a small socket in the egg shell, usually located at the base of the yolk sac. It is part of the structure of the eggs of birds and reptiles. Deuterocoels are present in the eggs of birds, reptiles, fish and amphibians. This is the only known example of an organic membrane covering the outer shell of an egg.

The name deuterocoel comes from the Greek words dêteros (second) and kois (empty, hollow). These words are due to the fact that the deuterocoel contains a cavity filled with liquid material, which is different from the liquid inside the shell. This liquid is a mixture of yolk and water, which is a source of nutrition for the developing embryo.

Deuterocoels are found in most birds and come in a variety of shapes and sizes. In reptile eggs they are usually very small and are found only inside the yolk. In large eggs of some birds (for example, ostrich, peacock), the deuterocoels may be large enough to be visible on the surface of the shell.

The structure and purpose of deuterosels is the subject of a large amount of scientific research. However, in general they play an important role in providing optimal nutrition to the developing embryo and protecting it from external influences. In addition, the presence of deuterocyls in different bird species may be related to various evolutionary aspects, including environmental adaptation factors and behavioral traits.