According to Des Cilleuls, interstitial cells are first found in males about 30 days old and at this time the secondary sexual characters put in their appearance. If, as will be shown in the sequel, he means by interstitial cells the endocrine cells that suppress the development of the male plumage in the female, the appearance of these cells at this time would be significant; but if he implies that their occurrence in the male incites the development of the secondary sexual characters, his interpretation is open to serious doubt. Reeves found interstitial cells in testes of cocks 3, 5½, 9, and 18 months—more in the earlier stages.
In a later communication by Boring and Pearl the whole question is taken up again with improved methods, etc. Previously 21 male birds had been studied, just hatched to 12 months old. More sections of this same material were made which were stained according to Mann’s and Mallory’s methods. In addition, a whole new series of preparations was made. A few interstitial cells, i. e., granule containing-cells were found in newly hatched chicks, but not in any of the 60 mature birds examined.
LUTEAL-CELLS IN THE TESTES OF THE MALE SEBRIGHT.
Finding that the testes of F₂ hen-feathered birds were often flat and pear-shaped instead of rounded and cylindrical, as in ordinary cocks, and that they were often black in color, suggested, as already stated, that the testes of the Sebright might be hermaphrodite in some element. It seemed not impossible that egg-cells might be found. I made a considerable number of sections of the testes of these birds and examined them under the microscope; not finding any egg or egg-like bodies, the slides were laid aside, but the idea that in some other way the Sebright’s testes might correspond to the ovary of the female next recurred to my mind. Consequently, when in the summer of 1918 I had some new material derived from a castrated Sebright male that had partly regenerated its testes and was again going back to hen-feathering, and pieces from one of the old testes of a castrated bird, I asked Miss Boring, who was then in Woods Hole, to make some preparations and examine them to see if she could detect any such elements in them as she had found in the female. Miss Boring reported the occurrence of luteal cells in the testes from hen-feathered males, and the results have been published in a brief preliminary paper (1918). The abundance of these clear cells, supposedly gland-cells with endocrine influences, in the testes of hen-feathered birds is in sharp contrast to their absence in the normal adult cock birds. It seems to follow, therefore, that the hen-feathering in the Sebrights is due to the presence of these cells, whose function is the same as of the similar cells in the female, i. e., the suppression in both of cock-feathering. Castrating the Sebright produces its effect by the removal of these cells that are responsible for the suppression of cock-feathering.
The occurrence of luteal cells in young stages of other races of poultry raises the question as to whether in these races the first or juvenile plumage, that resembles that of the hen rather than that of the cock, may not also be due to an internal secretion from these cells, or whether this juvenile plumage is only the plumage of a characteristic stage in development. Castration of young chicks ought to settle this point. Such castration experiments have been made by Goodale. The absence of any reference to any effect on the juvenile plumage in these early castrated birds probably meant that they did not develop precociously cock-feathering, and he writes me that he examined them carefully and that their plumage is like that of the normal chicks. Geoffrey Smith has reported the occurrence of two kinds of males in a race of Leghorns, the males of one of which become cock-feathered before the other. May not this difference depend on the length of time endocrine cells remain or begin to develop? A histological study of the two types would be of the greatest interest.
ENDOCRINE CELLS IN THE TESTES OF MAMMALS.
In man and other mammals it has long been recognized that in addition to the germinal cells of the testis there are also present other cells, sometimes called interstitial cells, that, so far as known, have no immediate function in connection with the germ-cells, or at least that have other important functions outside the relation to the reproductive organ. That some internal secretion from these cells has an important influence on the secondary sexual characters rather than anything done by or produced by the germinal cells has been very clearly shown by evidence derived from three separate sources, namely, from the operation known as vasectomy, from an exceptional condition known as cryptorchidism, and more indirectly from X-ray treatment. Vasectomy involves either cutting the vasa deferentia in such a way that the cut ends do not reunite. In consequence of the closure of the outlet of the testis the germinal cells slowly degenerate, and finally completely disappear. How such an effect is produced we do not know. That this result does take place is borne out by the unanimous testimony of all those who have successfully performed the operation. Ancel and Bouin showed (1903) that breaking the continuity of the vas deferens suppressed spermatogenesis in 8 to 12 months. Both the Sertoli cells (the nourishing cells of the germinal epithelium) and the interstitial cells persist. Such animals remain sexually active and their secondary sexual characters are not affected. Marshall states that in the hedgehog the remarkable periodic enlargement of the testis takes place even after vasectomy, although the germ-cells have disappeared.
In mammals the testes fail at times to pass through the inguinal canal, and, in consequence of their retention in the body-cavity, the germ-cells fail to develop. On the other hand, the interstitial cells of the testis develop normally. Cryptorchid individuals show the normal secondary sexual characters of their species. How retention of the sperm should give rise to the same result as cutting the duct, viz, absorption of the germinal cells, is not known. A possible solution may be found in the pressure exerted on the testes, both when retained in the abdomen and when their outlets are stopped by tying or cutting the ducts.
Finally, it has been long known that continued or repeated exposure to X-rays or to radium causes the destruction of the germ-cells, but leaves the interstitial cells intact and presumably functional. Destruction of the germ-cell by X-rays has no effect on the secondary sexual characters.
This threefold evidence demonstrates that in the male of the mammalia most, perhaps all, of the secondary sexual characters that are affected by castration are not affected by the destruction of the germ-cells. This conclusion supports very strongly the view that the interstitial cells are the cellular element in the testes that influence through internal secretion the development of the secondary sexual characters of the male.