XII.—Studies in Embryonic Mortality in The Fowl. III. Chick Monsters in Relation To Embryonic Mortality

Abstract

SummaryIn an examination of 11,797 eggs which had failed to hatch, 433 specimens exhibiting teratological abnormalities were obtained.The various types of monsters observed are briefly described and the frequency of each given.The most common types were characterised by various degrees of abnormality either in the brain, cranium, or eyes, or in two of these structures, or in all three. Hyperencephaly, exencephaly, and microphthalmia constituted 93 per cent. of all the monsters observed.Other teratological abnormalities encountered included prognathia, duplicity, ectopia, cyclopia, otocephaly, malformed limbs, and absence of premaxillæ.Monsters accounted for at least 3·6 per cent, of all mortality in the material examined.Since this material included many embryos too decomposed for detection of teratological abnormality, the actual loss is probably considerably higher.No significant deviations from the normal sex-ratio were evident in any class of monsters.A decline in the frequency of such abnormalities from February to April was evident.Evidence is adduced from Stockard's experimental teratology in fish eggs, to show that a very probable cause of the production of monsters in the chick is an arrest of development of the embryo at a critical stage.Presumably such a condition results from the chilling of those eggs laid in the early stages of gastrulation.Some evidence to indicate the possibility of an hereditary tendency to produce monsters is briefly discussed.