X.—Studies in Embryonic Mortality in the Fowl. I. The Frequencies of Various Malpositions of the Chick Embryo and their Significance

Abstract

Summary1. An examination has been made of 11,797 eggs which had failed to hatch, among which were 5050 embryos which had died after the eighteenth day.2. Four major malpositions of the chick embryo are described and the frequency of each given.3. It is concluded that one of these, in which the head is buried between the legs, definitely prevents hatching. In the material examined, this abnormality was responsible for 9·25 per cent. of the mortality among embryos of eighteen days or over.4. It is suggested that the other three malpositions usually result fatally, by reason of their preventing pulmonary respiration in the embryo as well as by mechanical hindrance.5. Of the embryos over eighteen days, nearly 56 per cent. were in one or another of the four major malpositions.6. Possible causes are discussed, and the suggestion made that some of the abnormal positions result from an incorrect orientation of the embryo established early in cleavage.