No. 516] COPULATION A3IOXG CRAWFISHES 751 



In twelve of the trials copulation took place first in the 

 light; in fourteen cases the pair in the dark copulated 

 first, and in the other two instances the two pairs occupied 

 the same period of time in becoming united. Twenty- 

 eight different individuals were given twenty-eight op- 

 portunities to copulate and approximately an equal num- 

 ber of " first " copulations took place in the light and 

 the dark. From these experiments it appears that condi- 

 tions of light stimulation are apparently of little conse- 

 quence, at least where individuals which are in a state of 

 excitement are concerned. 



Attempts were made to arouse males to a state of activ- 

 ity by adding extracts to the surrounding medium. The 

 males were separated from their mates and allowed to 

 become quiet in a dish of clean water. Various portions 

 of females which had been recently copulating were then 

 added, and although pieces of ovary, pieces of abdomen 

 and extracts from these organs and from the whole body 

 were used in this way, nothing but negative results were 

 obtained. The males remained quiet and exhibited no 

 signs of excitement within half an hour after the portions 

 of the female's body had been added. From these results 

 it does not seem probable that copulation is brought 

 about by the action of any secretion given off by the 

 female which might serve to excite the male. 



The results of all the experiments described indicate 

 that sexual union is more or less a matter of chance. Tf a 

 male and a female which are in the proper physiological 

 condition come together they will copulate with equal 

 readiness in the light or dark. Neither sex can be said to 

 be wholly responsible for the act of sexual union and 

 although the male usually assumes the active part, it is 

 not an invariable rule. An instance was observed in 

 which one female fought almost continuously with another 

 for over two hours. When this pugnacious individual 

 was placed in a dish with several males she walked about 

 actively and grasped them with her chela?, but as soon as 

 one of them grasped her and attempted to turn her over, 



