625 



experiments rests on the supposition that after castration the papillae 

 (rapidly) disappear and never grow again. Dr. Schuster and I pointed 

 out in our paper that the effect of castration is not to make the papillae 

 immediately disappear; that indeed six months after the operation 

 marked papillae might still be present. This fact is clearly a source of 

 error in experiments where injections are made within six months of 

 castration by an observer who is under the impression that the papillae 

 have completely disappeared when they may not have done so. But in 

 some of Professor Meisenheimer's experiments the injections or im- 

 plantations of testes and ovaries were not made until a year after the 

 castration was performed. In these cases the frogs had passed through 

 a summer and had presumably acquired smooth thumbs, so that their 

 acquisition of papillae the following autumn might certainly be ascribed 

 to the experimental treatment, provided that a re-growth of pa- 

 pillae in a castrated frog without further treatment never 

 occurs. If it does occur, (and the experiment described in this paper 

 shows that it does) , there is no need to ascribe the re-growth observed 

 by Prof. Meisenheimer to the injections of testes and ovaries, because 

 it would take place in the normal course of events. It is obvious that 

 the re-growth of the papillae on the thumb more than a year after 

 castration without any further experimental treatment and after the 

 thumb had been perfectly smooth, entirely destroys the value of all ex- 

 periments performed on the supposition that such an event could not 

 occur. 



While thoroughly confirming Dr. Schuster and myself in the be- 

 lief that no evidence exists sufficient to prove that injection of testes or 

 ovarian extracts or implantation of testes or ovaries can call forth the 

 growth of papillae on the thumb of a castrated frog, the experiment re- 

 corded in this paper, together with others of a similar nature, necessi- 

 tates the modification of our views in one particular. 



We adopted the view that the smooth tumid condition assumed by 

 the thumb of a normal male during the summer months was due not so 

 much to the casting off of the papillae, as to the growth and thickening 

 of the epidermis of the pad. While fully convinced that this growth and 

 thickening does occur in the summer months in normal male frogs, it is 

 clear that the pad may become smooth without any marked growth and 

 thickening. This is clearly shown in the experiment recorded in this 

 paper where the thumb pad became ultimately quite smooth without any 

 active thickening or increase in size. The fact that this increase did not 

 occur in the castrated frog probably accounts for the comparatively 

 small size of the papillae subsequently produced. It will be remem- 

 bered that in the normal male frog the annual growth and activity of 



Zoolog. Anzeiger. Bd. XLI. 40 



