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Sci Tech
Respiration inside egg
How does a poultry chick breathe inside the egg?
S. Prakash
Kovai, Tamil Nadu
During the development of a chick special structures develop as devices to enable the egg to be laid and develop on land. The embryo is covered by a fluid filled covering known as omnion which protects the it from mechanical shocks and desiccation.
The reserve food (yolk) is covered by a sac known as yolk sac which is connected to the midgut of the embryo. Yet another outgrowth takes place from the hindgut that penetrates the space between amnion and the yolk sac. This outgrowth is called allantois.
The allantois and the hindgut are connected by a narrow allantoic stalk which later joins with the yolk sac to form the umbilical cord. The amnion, yolksac and allantois are all covered by a membrane called chorion. The chorion is again covered by shell membranes and a calcareous shell.
During incubation period, the allantois spreads over the complete surface of the egg underneath the chorion and form chrio-allantois.
This lies close against the egg’s calcareous shell which is porous. A network of capillaries develops on the external surface of chorio-allantois and the network is in communication with the embryo proper by blood vessels running along the stalk of allantois and through the umbilical cord.
The chorio-allantoic circulation continues until the young chick breaks the egg-shell and begins to breathe the atmospheric air. Thus the chorio-allantois serves as respiratory surface.
K. Venkataraman
Retd. Reader in Zoology, Madura College
Madurai, Tamil Nadu
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