Respecting the Alytes bred in this way Kammerer makes the very striking statement that the males in the third generation (p. 535) have roughened swellings on their thumbs and that in the fourth generation (pp. 516 and 535) these swellings develop black pigment. Together with the appearance of this secondary sexual character there is hypertrophy of the muscles of the fore-arm. To my mind this is the critical observation. If it can be substantiated it would go far towards proving Kammerer's case. Alytes, among toads and frogs, is peculiar in that the males do not develop these lumps in the breeding season, and the fact may no doubt be taken to be correlated with the breeding habits, copulation occurring on land and not in water as is usual with Batrachians. It is to be expressly noticed that these lumps on the thumbs or arms of male toads and frogs are not merely pigmented swellings, but are pads bearing numerous minute horny black spines, which are used in holding the females in the water. The figures which Kammerer gives (Taf. XVI, figs. 26 and 26a) are quite inadequate, and as they merely indicate a dark patch on the thumbs it is not possible to form any opinion as to the nature of the structure they represent.
The systematists who have made a special study of Batrachia appear to be agreed that Alytes in nature does not have these structures; and when individuals possessing them can be produced for inspection it will, I think be time to examine the evidence for the inheritance of acquired characters more seriously. I wrote to Dr. Kammerer in July, 1910, asking him for the loan of such a specimen[13] and on visiting the Biologische Versuchsanstalt in September of the same year I made the same request, but hitherto none has been produced. In matters of this kind much generally depends on interpretations made at the time of observation; here, however, is an example which could readily be attested by preserved material. I notice with some surprise that in a later publication on the same subject no reference to the development of these structures is made (see below).
The statements here given represent but a small part of Kammerer's papers on the subject. He gives much further information as to the course of the experiments, especially in regard to the fate of the eggs laid on land and the aberrations induced in them by treatment. The ramifications of the experiments are, however, very difficult to follow, and as I am not sure that I have always understood them I must refer the reader to the original.
More recently Kammerer has published[14] a most curious account of experiments in crossing his modified and abnormal Alytes, derived from the water-eggs, with normal individuals.
In the first case the cross was made between a normal female and an abnormal male. The offspring were normal in their habits. In the next generation bred from these almost exactly a quarter showed the abnormal instinct.
The reciprocal cross was made between an abnormal female and a normal male. In this case the offspring were abnormal in their behaviour; but the second generation bred from them showed three quarters abnormal and one quarter normal.
Certain details as to numbers and sexes of the various families bred in the course of this amazing experiment are given in a subsequent publication.[15] This later paper goes somewhat fully into the question of the difference in behaviour between the normal and modified individuals, describing the ways in which the males and females possessing the acquired character could be recognised from the males and females which were normal, but in this account I find no reference to the development of the "Brunftschwielen"—the horny pads on the hands of the males. As these structures would be of special value in such a diagnosis the omission of any allusion to them calls for explanation. Kammerer claims the evidence as proof of Mendelian segregation in regard to an acquired character, the first example recorded. Pending a repetition of the experiments there is no more to be said.
2. The Mode of Reproduction of Salamandra atra and maculosa.[16] mdash;Salamandra maculosa, the common lowland form, with yellow bands or spots, deposits its young in water, generally as gill-bearing tadpoles, with a wide, swimming tail, though occasionally they are born still enclosed in the egg-capsule out of which they soon hatch. Spawning extends over a considerable period, often many weeks, and during the season one female may bear more than 50 young.
S. atra, the black Alpine form, produces its young on land. They are born without gills, ready to breathe air, and with the rounded tail of the adult. These differences may, as Kammerer says, naturally be regarded as adaptations to the Alpine conditions. Moreover, the female bears only two young in a season, and this reduction in the number must be taken to be a consequence or condition of viviparity. There are many eggs in the ovary, but all except the two which are destined to develop degenerate and form a yolk-material on which these two survivors feed.
Kammerer gives a long account of the various conditions to which he subjected both species. The treatment was complicated in many ways, but the essential statements are, as regards S. maculosa, that when no water was provided in which the young might be born, they were dropped on land, larger and in a later stage of development and of a darker colour than is normal; that the larvae so born gradually diminished in number until only two were deposited in each breeding-period; that dissection showed that the other ova degenerated to form a yolk-material. The larvae so produced reached maturity. The summary of results describes their behaviour, stating that they produced: