232 Studies in Animal Behavior 



The instinct to clasp is one of great strength and 

 male toads may suffer their bodies to be cut in two 

 without relinquishing their hold on the female. 



Correlated with the appearance of the breeding 

 instinct there occurs increased development of the 

 inner digital muscles and certain other parts of the 

 fore legs of the males, a development which Nuss- 

 baum has shown to be checked if the males are cas- 

 trated a considerable time before the onset of the 

 breeding season. Probably as a result of internal 

 secretions of the reproductive glands, parts of the 

 neuro-muscular mechanism become at this time pecu- 

 liarly irritable, so that a particular form of reflex 

 activity is very easily evoked. But notwithstanding 

 this, a frog or toad seldom clasps for long anything 

 but the female of his own kind. Other males may 

 be clasped, but they are usually soon relinquished, 

 while a female is clasped the more firmly the longer 

 she is held. 



How does the frog distinguish male from fe- 

 male ? Goltz has found that blinded frogs discrimi- 

 nate between the sexes as well as normal frogs. 

 After the olfactory nerves were cut he found that 

 males can still distinguish females, so that neither 

 sight nor smell is a necessary element in the recog- 

 nition of sex. Even when the males were robbed 

 of both sight and the sense of smell many of them 

 succeeded in clasping the females among which they 

 were placed. When the females were rendered 

 mute by an operation they were no longer seized. 



