Ferry, James F. Department of Biology, Madison College, Harrisonburg, Virginia.
Ackerman, Ralph A. Department of Zoology, Iowa State University, Ames, Iowa.
Last reviewed:October 2020
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- Egg water balance
- Respiratory gas exchange
- Related Primary Literature
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A single, large, living, female sex cell enclosed in a porous, calcareous shell through which gases may pass. Birds considered to be fowl are divided into two orders: Galliformes (landfowl) and Anseriformes (waterfowl). Although they vary in size, shape, and color, the eggs of various fowl, including chickens (Fig. 1), ducks, geese, and turkeys, are essentially the same in structure and content. Inward from the shell are the outer and inner shell membranes, which are also permeable to gases. The membranes are constructed to prevent rapid evaporation of moisture from the egg, but they allow free entry of oxygen, which is necessary for life. Air begins to penetrate the shell soon after the egg is laid, and it tends to accumulate in a space between the two membranes at the large end of the egg. See also: Anseriformes; Aves; Cell (biology); Galliformes
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