STUDIES IN THE EXPERIMENTAL ANALYSIS OF SEX. 467 
given to account for the action of Sacculina on crabs, and for 
the dependence of the comb-growth of hens on reproductive 
activity, and it accords with our results, on male frogs at least, 
equally as well as the theory of internal secretion. 
Summary. 
(1) The cyclical changes in the testes and thumb of male 
frogs are described. It is found that after the breeding 
season, although the outer papillated layers of the thumb- 
pads are thrown off, yet the pads do not immediately become 
smooth, papillae of considerable size being present in the 
early summer months. The assumption of the perfectly 
smooth condition takes place gradually during the summer, 
and is due, not to a process of reduction, but to a prolifera- 
tion of the epidermis which fills in the valleys between the 
papilla. 
(2) Transplantation of testes into other individuals, whether 
male or female (allo-transplantation), leads to the breaking-up 
and degeneration of the ripe spermatozoa and the testicular 
tissue, and its replacement by fibrous tissue, the greater part 
of which is derived from the host and invades the degenerate 
testis from the place of attachment to the host’s body. 
Testes transplanted into the peritoneal cavity of another 
individual always become attached to the peritoneal lining 
and rapidly vascularised. Phagocytosis plays an important 
part in the absorption of the degenerate spermatozoa. 
(3) When the testes are simply severed from their con- 
nections in the body and left unattached in the peritoneal 
cavity of the same individual (auto-transplantation), they 
soon acquire new attachments and vascularisation. The ripe 
spermatozoa rapidly degenerate and are finally replaced by 
fibrous tissue, partly, at any rate, derived from the testis itself, 
but the spermatogonia of the peripheral tubules survive, and 
proliferate in an active manner. This survival of the 
germinal cells in the case of auto-transplantation never occurs 
in allo-transplantation. 
