Studies on the relation of gonadic structure to plumage characterisation in the domestic fowl.—II. The developmental capon and poularde

Abstract

Among the many sexually abnormal fowls sent to this Department during the last five years by poultry keepers interested in the science of breeding have been eleven birds which together form a distinct class. Instead of developing into normal cocks or hens with appropriate male or female plumage and head furnishings as they approached maturity, these birds assumed, and retained throughout their lives, the characters and behaviour of the fowl completely gonadectomised before puberty. There was never any reason to assume that the underlying physiological inactivity or actual absence of the gonads was other than the result of some developmental disharmony. No sign or history of disease was ever presented. Our knowledge of the adult characterisation of the fowl experimentally gonadectomised when a few days old, allowed us to recognise that in this group of sexually abnormal birds there were genetic males and females in which the gonadic tissues had been absent or functionally insufficient throughout their lives. In one respect only did these birds (save one) differ from the experimental capon and poularde; their combs were not bloodless and scaly, they were bright and healthy-looking, though very diminutive. After having been kept under observation for two years or more, the birds were killed. Post-mortem examination confirmed our anticipations. In all, there was either complete suppression or else very considerable reduction of gonadic tissue. Such cases as these have an important bearing upon the problem of the relation of gonadic structure and function to plumage characterisation in the fowl. The following cases of gonadic suppression and reduction in birds have been recorded : one duck, Netta rufina, with imperfect male characters and no gonads (Poll, 1909); four pheasant hybrids, Phasianus torquatus X P . colchicus (?) (Smith and Haig Thomas, 1913); Syrmatiens recessi X Phasianus principalis , reciprocal crosses, all females had small flaccid oviduct but no gonadic tissue (Phillips, 1916); pigeons and ringdoves, pure bred and hybrid, sixteen with no gonads, fifteen in which one gonad was abnormally absent, seventeen in which various degrees of reduction in the size of the gonads were exhibited (Riddle, 1925).