164 EVIDENCE OPPOSED TO 



proliferate, forming groups of cells known as sper- 

 matocysts. In June and July spermatogenesis is 

 active, and from August to October the formation of 

 ripe spermatozoa is completed. 



Tlie corresponding changes in the thumb-pads 

 are as follows. Immediately after the breeding 

 season the horny epidermis of the pad with its 

 deeply pigmented papillae is cast off, and the 

 thumb remains comparatively smooth from April 

 or May until August or September. When the 

 large papillae are shed, smaller papillae remain 

 beneath, and are gradually obliterated by the 

 epidermis growing up between them. The epidermis 

 is therefore growing while the spermatogenesis is 

 taking place. In August and September the epi- 

 dermic papillae begin to be obvious, and from this 

 time till February a continuous increase in the 

 papillae and their pigmentation occur. Geoffrey 

 Smith argues that the development of this somatic 

 character occurs while the testes are inactive and 

 unchanged. Considering that the testes throughout 

 the winter months are crammed with spermatozoa, 

 which must require some nourishment, and which 

 may be giving off a hormone all the time, the argu- 

 ment has very little weight. Smith and Schuster 

 found that ovariotomy, with or without subsequent 

 implantation of testes or injection of testis extract, 

 had no effect in causing the thumb of the female to 

 assume any male cliaracters. 



Castration during the breeding season causes the 

 external pigmented layer with its papillae to be 

 cast off very soon — that is to say, it has the same 

 effect as the normal discharge of the spermatozoa. 

 Smith and Schuster found that castration at other 



