Champy (1921) records that when a male triton (T. alpestris) was fed intensively after the 'winter's starvation period, he assumed the external characters of a female, and that within the pre-existing testicular tissue there were to be found immature, but unquestionable ova. He had previously shown that the annual process of spermatogenesis in tritons could be inhibited by starva tion and that in the absence of spermatogenesis there was no development of external sexual characters, the animal exhibiting the "neuter" state characteristic of winter. In this "neuter" state there are to be found in the testes primitive gonocytes and spermatogonia. In animals killed in the spring, following starva tion, the testis was represented by a longitudinal strip of fat. Two of these starved "neuter" tritons, when fed intensively, lost the dark blue coloration of the back and assumed a greenish shade mottled with distinct blue marks, as in the female, whilst the yellow dorsal line became more and more attenuated. One of these animals was killed in January and there was found the expected strip of fat with a few spermatogonia. The other was kept alive and in February was female in appearance. It was kept until April when post-mortem examination revealed within each of the strips of fat an elongated organ of granular appear ance resembling an ovary, together with an oviduct.
In addition to these experimental studies in sex-reversal, the following cases have been observed. In the case of one of the frogs resulting from the "egg-overripeness" experiments, Witschi (1923) was able to show that indeed it was a transformed female, for when mated with a normal female it sired only female off spring. This is as would be expected, if in its fundamental chromo some constitution it still remained XX, for then all its spermato zoa would be X-chromosome-bearing and on fertilising X-bearing eggs would yield none but XX zygotes. Crew (1921) had previ ously encountered a similar case in the frog.
Riddle observed a case of complete sex-reversal in the ring dove (Streptopelia risoria) an adult female laid eleven eggs be tween January 17 and April 15, 1914. During the six months following she and a male mated three times, began sitting on a nest without producing eggs, and raised young of other parents.
During the following nineteen months her sex-behaviour and mode of growing changed to that of a male, frequently forcing her male mate to act as a female in copulation. At twenty-two and a half months after producing her last egg, this bird and mate were transferred to a pen with a few other spent inactive doves. The male of this pair died three and a half months later, and weights and dimensions of testes were obtained. Twenty one months after transfer, the bird died, showing advanced ab dominal tuberculosis. Two testes were found, removed and weighed. If any residue of the original ovary remained it was wholly included in a tuberculous mass, involving spleen and liver. At the time of autopsy this bird was supposed to be the
original male of the pair, and therefore the testes were not saved for demonstration. The bird had lived forty-four and a half months after producing the last egg, became tuberculous, assumed male behaviour, the curve for the body weight during the three years undergoing a remarkable change, and at death it possessed two unmistakable testes. Riddle interprets this transformation as the result of the increased metabolism which followed the destruc tion of the ovarian tissue and the presence of tuberculosis.
Crew (1923) described the case of a Buff Orpington hen, the reputed mother of many chickens, which when three years old was attacked by tuberculosis and developed male characters, to become a fecund male and the father of two chickens. Post mortem examination revealed the presence of two functional testes and a highly degenerate mass of ovarian tissue destroyed by tubercular disease. This case alone could not be regarded as providing conclusive proof of sex-reversal in the fowl, for during the earlier part of its life this bird had been in the possession of a private breeder concerning whose integrity there is no doubt but whose powers of critical observation can, of course, be held up to question. However, Crew (1923) and Fell (1923) examined a series of sexually abnormal fowls and were able to demonstrate that the condition found in these could logically be interpreted as stages in the process of transformation from a female type of sex-organisation to a complete male type.
In the mammal complete sex-reversal cannot occur in post embryonic life, because of the differential mode of development of the internal and external sex organs.
A consideration of these instances of sex-reversal will show that in the egg stage and in the post-embryonic stage of Amphibia and in the case of fish also, if Huxley's interpretation of Bou lenger's results is correct, reversal can occur in either direction, female to male, and vice versa, whereas in the post-embryonic stage of birds it has thus far been demonstrated in one direction only, from digametic sex to monogametic. In this connection it is of interest to note that in the instances of intersexuality in Lebistes observed by Winge (1927) the change occurred in old females which assumed male characters though still breeding as normal females. That this is so is provocative of thought. It is possible that the balance between male and female sex-differ entiating reactions is more easily disturbed in the case of the sex which possesses but a single X-chromosome, a suggestion which is in line with the observation of Haldane (1921) that in the case of specific and wide varietal crosses if among the offspring one sex is absent, rare or sterile, that sex is the digametic.