The Genetic And The Operative Evidence Relating To Secondary Sexual Characters
9781465650252
213 pages
Library of Alexandria
Overview
There are a few races of poultry that have two kinds of males, one with the feathering of the ordinary cock, the other with the feathering of the hen. The Hamburgs and the Campines are perhaps the best known races of this sort. Convention amongst breeders, in certain countries, has determined that the cock-feathered bird shall be the standard, and at other times and places that the hen-feathered males shall be the show birds. In one breed, at least, viz., the Sebright bantams, the hen-feathered cock is the only known type. Cock-feathered Sebrights have never been seen, so far as I know. This breed is pure for hen-feathering. The male Sebright lacks the long, pointed saddle feathers at the base of the tail of the common cock, also the peculiar back and neck feathers (hackles) of the cock bird, as well as the male feathering on the bow of the wing. His feathers in these parts are almost exactly like those of the hen. The long sickle feathers covering the true tail are also absent, although the two median ones sometimes occur in males of this race. The Sebrights seemed excellent material for studying the heredity of this type of plumage in the male. In 1911 I began to study this problem, and crossed Sebrights to Black-Breasted Game bantams. The latter race was chosen not only because the males have the typical cock-feathering, but also because the coloration of these birds resembles very closely that of the jungle-fowl, from which many, perhaps all, of our domesticated races have sprung. In dissecting some of the F₂ birds from this cross I noticed that the testis of the male was often more flattened than is the testis of the typical male bird, that it was often somewhat pear-shaped, and that frequently it was in part or entirely black. Recalling that male Sebrights are said to be often partially sterile, the idea naturally suggested itself that these birds are hen-feathered because the testes have assumed some of the characteristics of the ovary. It had long been supposed, and had been finally established by Goodale, that the presence of the ovary in the female suppresses her potential development of plumage, for when the ovaries of the hen are diseased or removed she develops the plumage of the male. This reasoning led me to try the experiment of castrating the hen-feathered males in order to see if they would become cock-feathered. The outcome was immediately apparent; the new feathers were those of the cock bird. While the “reasoning” that led to the experiment is open to serious question, nevertheless the “hint” furnished by the unusual condition of the testis led finally to the discovery that luteal cells were present in abundance in the testes of the male Sebright like those present only in the females of other breeds. Whether or not the shape of the testis of the Sebright, that is sometimes like that of the ovary, is connected with the unusual abundance of luteal cells in the testis I do not know. If so, then the hint that came from their shape was not so unreasonable as appears at first sight. The birds first operated upon were adult F₁ and F₂ hen-feathered birds. The first one done by myself died, but a few, whose testes were removed by Dr. H. D. Goodale at my request, lived and changed to cock-feathered birds. Since then I have operated successfully on a number of F₁ and F₂ birds, as well as Sebright males. In these operations I have had throughout the assistance of Dr. A. H. Sturtevant and for two years the assistance of Dr. J. W. Gowen also. I wish to express my appreciation of their help and advice, for without it I doubt whether I could have carried out the work successfully. Since the main interest attaches to the Sebright experiments, they will be described first, although they were the last to be performed.
