Diseases of poultry; their etiology, Diseases of poultry; their etiology, diagnosis, treatment, and prevention diseasesofpoultr01pear Year: 1915 Diseases of the Reproductive Organs 275 only two tenths of 1 per cent of the eggs are double-yolked. The ratio of double to single yolked eggs is less than twice as high as the ratio of twin to single births in the human family. All birds are not equally likely to lay double-yolked eggs. In fact the great majority of birds never lay anything but single-yolked eggs. There are, however, birds which possess a tendency to lay double-yolked eggs. Such an
Diseases of poultry; their etiology, Diseases of poultry; their etiology, diagnosis, treatment, and prevention diseasesofpoultr01pear Year: 1915 Diseases of the Reproductive Organs 275 only two tenths of 1 per cent of the eggs are double-yolked. The ratio of double to single yolked eggs is less than twice as high as the ratio of twin to single births in the human family. All birds are not equally likely to lay double-yolked eggs. In fact the great majority of birds never lay anything but single-yolked eggs. There are, however, birds which possess a tendency to lay double-yolked eggs. Such an individual may produce several such eggs. It has been further found Fig. 56. — Triple-yolketl cj; (.Uriginal.) that a bird which possesses the tendency to lay double- yolked eggs is not equally likely to produce them at any age. She is most likely to produce them when she is young. Eighty per cent of all the double-yolked eggs produced by the Station flock are produced by birds less than eight months old. We have only a very few records of birds which have laid double-yolked eggs after their first adult molt. It has been usually supposed that double-yolked eggs are caused by the simultaneous entrance of two yolks into the egg tube and the consequent common passage of the two
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