748 THE AMERICAN NATURALIST [Vol. XLIII 



over in some cases, they always eventually succeeded in 

 freeing themselves. After these males had been allowed 

 to " fight " thus among themselves for from half an hour 

 to two hours (the time varied in different experiments) 

 they became comparatively quiet and finally came to rest 

 in a group at one side of the dish in such a way that their 

 bodies were in contact with each other. After they had 

 remained in this condition of rest for at least half an 

 hour a female which had just been released from copula- 

 tion with a different male was gently introduced into the 

 dish with them. 



In all five of the experiments the female moved about 

 the dish and came in contact with one or more of the 

 males, and sometimes she even walked over them, but 

 nevertheless there were only two attempts at copulation 

 within half an hour after a female had been placed in the 

 dish. In one of these cases a male attempted to grasp 

 another male after the female had been introduced, but 

 he soon desisted from the attempt and all the individuals 

 in the dish then became quiet again. In the other instance 

 one of the (two) males attempted to turn over the female 

 as soon as she came in contact with him (not as soon as 

 she was introduced into the dish). These experiments 

 showed that males which had recently been in active copu- 

 lation were not necessarily induced to copulate again by 

 the immediate presence of an active female. 



Five other experiments were performed which were 

 similar to those just described except for the fact that 

 the female was introduced into the dish with the males 

 before they had come to rest. In this second series copu- 

 lation took place within half an hour in every case. The 

 results make it appear that the readiness with which copu- 

 lation is undertaken by a pair of crawfishes depends upon 

 the physiological state of the male, for, as Andrews has 

 stated, the male usually takes the active part in the ma- 

 ting reactions, while the female remains passive. 



Another series of observations showed that the readi- 

 ness with which copulation takes place depends largely 



