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Page:Popular Science Monthly Volume 81.djvu/372

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366
THE POPULAR SCIENCE MONTHLY

duct, is not enough to insure that a hen shall lay eggs, that is, exhibit actual as well as potential fecundity. While comparatively very rare, cases do occur in which a bird possesses a perfect ovary and perfect oviduct and is in all other respects entirely normal and healthy, yet never lays even a single egg in her life time. Such cases as these prove: first, that what we may call the anatomical factor is not alone sufficient to make potential fecundity actual; and second, that the anatomical and physiological factors are distinct, in the sense that the normal existence of one in an individual does not necessarily imply the coexistence of the other in the same individual.

Turning now to the physiological factors involved in fecundity, it would appear that there are at least two such factors or groups of factors. The first of the physiological factors involved may be designated the "normal ovulation" factor. By this is meant the complex of physiological conditions which, taken together, determine the laying of about such a number of eggs as represents the normal reproductive activity of the wild Gallus bankiva. It must be remembered that, for reasons which can not be gone into here, under conditions of domestication the activity of this normal ovulation factor will mean the production of considerably more eggs than under wild conditions. Egg production involves certain definite and rather severe metabolic demands, which under wild conditions will not always, or even often be met. Further, as has been especially emphasized by Herrick, egg-laying in wild birds is simply one phase of a cyclical process. If the cycle is not disturbed in any way the egg production is simply the minimum required for the perpetuation of the race. If, however, the cycle is disturbed, as, for example, by the eggs being removed from the nest as fast as they are laid, a very considerable increase in the total number of eggs produced will result.

It is a fact well known to poultrymen, and one capable of easy observation and confirmation, that different breeds and strains of poultry differ widely in their laying capacity. In saying this the writer would not be understood to affirm that a definite degree of fecundity is a fixed and unalterable characteristic by any particular breed. The history of breeds shows very clearly that certain breeds now notably poor in laying qualities were once particularly good. One of the best examples of this is the Polish fowl. But, in spite of this, not only do these breed and strain differences in fecundity exist, and probably always have existed, but they are inherited. Such inherited differences are independent of feeding or any other environmental factors. Thus a strain of Cornish Indian Games with which I have worked are poor layers, regardless of how they are fed and handled. This is merely a statement of particular fact; it does not imply that there may not exist other strains of Cornish Indian Games that are good layers.