444 
GEOFFREY SMITH AND EDGAR SCHUSTER. 
smooth thumbs in summer (July) show a thickened instead of a 
reduced epidermal covering (Pl. 46, fig. 32), the valleys 
between the papillae being filled up with epidermal tissue. I 
is quite right to argue, therefore, that during the summer? 
when the thumbs are becoming smooth and the testes are 
actively growing, that the thumb tissue is not undergoing 
reduction, but that an actual proliferation of epidermal tissue 
is taking place. The fundamental importance of these facts 
will be apparent when we come to criticise the experimental 
results obtained by Nussbaum (see p. 459, et seq.). 1 
The above facts apply to the species B. fusca = temporaria, 
with which all the succeeding experiments have been per- 
formed. It appears that in B. esculenta the cyclical 
changes are not so regular, and it is said that it is impossible 
to induce this species to breed or to go through its normal 
cycle in captivity. 
We will first of all give the results of our experiments in 
the transplantation of testes, and we will deal first with the 
cases of allo-transplantation, where the testis or testes of a 
male were transferred to the peritoneal cavity of a female 
frog. 
Allo-transplantation of Testes into Female. 
Seven successful experiments were performed, which may 
be considered in order according to the length of time the 
testes remained in the body of the female. 
No. 1. — Female frog, with one testis from male frog B., 
implanted September 29th, 1910. Killed November 8th, 
1 Although it is customary to speak of the thumb-pad increasing in 
size during the winter months before the breeding system, there is 
really very great doubt whether the increase in the number and size of 
the papillae which occurs then indicates any actual process of growth or 
increase in mass at all. There is an increase of the surface area of the 
pad owing to the folding involved in the formation of the papillae, but 
this does not necessarily mean any actual growth or increase of mass. 
Although it is difficult to prove, it appears very probable that the 
whole of the actual increase in mass or growth of the thumb-pad really 
takes place in the summer months when the pad is smooth. 
