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.