“In August and September the epidermal papillæ begin to be obvious, and from this time onwards until about February a continuous increase of the epidermal papillæ and pigmentation occurs. During the greater part of this time, when the thumb-pads are attaining their characteristic rough and pigmented appearance, the testes remain inactive and unchanged--a fact which has been too readily overlooked by writers on the correlation of the primary and secondary sexual characters.” Nussbaum (1909) and later Meisenheimer (1911) found that after castration the thumb-pads disappear. Smith confirms this report in all essential respects, although in certain details concerning the papillæ he does not agree with the two former observers. His results show that castration at the breeding-season is rapidly followed by the loss of the outer papillated layer of the thumb-pads, but castration at any other season does not have “any marked effect,” the papillæ remaining for 5 months and more in the same condition as at the time of castration. The essential point here, however, is that the excessive and even special development at the breeding-season does not take place nor is again assumed (apparently), if castration has taken place at some other time of the year. Smith and Schuster’s attempts to transplant the testes into other males or females were unsuccessful, as the testes degenerate after a time. Auto-transplantation of the testes were more successful. Removal of the ovary had no effect on the thumbs of the female, and even the injection of testes extracts into such females did not cause them to develop pads. Nussbaum and Meisenheimer had found that transplantation of pieces of the testes, and even injection of testes extract, into castrated frogs caused an enlargement of the thumb-pads. Smith shows that this conclusion rests on uncritical evidence. At any rate, his own more carefully planned experiments extending over the year show that the results obtained by Nussbaum and by Meisenheimer may be accounted for on other grounds than the effect of the injection or implantation. The following statement by Smith is not without interest, since it bears directly on an important question as to how internal secretions may produce their effects.