A Móra Ferenc Múzeum Évkönyve: Studia Naturalia 1. (Szeged, 1999)

Jakab Béla: A tojáshéj makro- és mikrostruktúrájának funkciói a költés folyamán

Summary The fertilized bird's egg, as a system of self preservation, contains the developing embryo and all of the necessary materials for the further development of the emb

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yo until hatching, except for the oxygen which sets in motion the mechanism of metabolism and the other outer conditions necessary for hatching, such as suitable temperature, humidity, ventilation and rotation of eggs, which are all provided by the brood-hen. The author describes the functions of exterior and interior conditions. He points out, in detail, that the cover of the eggshell is a wall between the above mentioned conditions. This eggshell, due to its layered structure, particularly the macro and microstructure, physical and geometrical characteristics, fulfills a very important role from the hatching point of view. The hatching constraints are completed with the protective role of the shell due to its solidity, which is related to the thickness of the shell. The solidity of the shell is due to its layering and other structures. The protective and hatching points of views are joined together in the form of the shell. In the prenatal period, the function of the shell in its contact with the chorion is highly important in diffusion respiration - the exchange of gases (0

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, C0

2

), and in the regulation of the degree of humidity (H

2

0). The pores, and even more so, the system of blood vessels in the chorion have a role in this process. From the connection of the allantois with the shell region, résorbent calcium is built into the body of the baby chick. Coming between the résorbent region of the allantois and the résorbent region of the chorion is an air chamber (at the larger end) which makes it easier for the chick to be hatched. The shell's optimal shape at the large end also helps in the hatching.