Responses of Feathers of Male and Female Pheasants to Theelin. ∗

Abstract

Some years ago it was observed 1 , 2 that in several species of birds and mammals a number of secondary sex differences, including color, seemed to be dependent on external or hormonal factors and not at all on the genetic sex of the individual. This discovery led to the enunciation of a theory of “equipotentiality” which assumed that male and female tissues are identical in their reactions, particularly to the sex hormones. Among birds the common fowl yielded much in support of this theory, for even in those breeds which show unusual types of reaction, as the Campines, 3 little evidence has been presented to show a difference between the two sexes. Nevertheless minor differences are suggested by the gonadectomy experiments of Finlay, 4 and the skin transplantation studies of Masui. 5 In the Reeves pheasant, which belongs in the same family as the domestic fowl, a marked constitutional difference in the behavior of feather follicles of opposite sexes has been found to exist. 6

An earlier report on these pheasants was concerned only with responses of male and female skin to normal concentrations of sex hormones, which could be tested by the method of skin transplantation. In a further study of Reeves pheasants and also members of the related genus Phasianus, it was found that the action of theelin injected intramuscularly is seemingly indistinguishable from that of the normal hormone of the bird's own ovary. Assuming that theelin and the ovarian secretions are essentially identical, the relative responsitivity of male and female feather follicles to the hormone may be compared fairly satisfactorily by means of skin transplantation, gonadectomy and theelin injection. While the results are rather clear cut, there is little doubt that they are obscured somewhat by the coincident action of other hormones than theelin 7 .