226 Studies in Animal Behavior 



collide they may curl up for a moment, but as they 

 are not seized they soon pass on. When two males 

 meet there is often a lively struggle. Each appar- 

 ently attempts to seize and carry the other, but as 

 neither will consent to remain passive they soon sep- 

 arate. The different reactions of the two sexes to 

 contact with other individuals is the factor which 

 effects the union of the males with the females. Each 

 reacts to the reactions of the other. The male has 

 a strong instinct to seize and carry other individuals 

 of the same species. The female has the instinct to 

 lie quiet when another individual comes into contact 

 with her, especially if she is seized. The instinctive 

 reactions of the two sexes are complementary, and 

 cooperate to bring about and maintain the peculiar 

 sexual association characteristic of the Gammaridea. 

 "If the association of the sexes is brought about 

 by their peculiar modes of reaction to certain contact 

 stimuli, it would seem probable that the only reason 

 why males do not carry other males as well as 

 females is that they are prevented from so doing by 

 the active resistance of their intended mates. I was 

 accordingly led to try the experiment of mutilating 

 some male specimens so that they could no longer 

 make effective resistance to seizure. The large sec- 

 ond gnathopods (the principal means of defense) 

 of several males were cut off and the mutilated indi- 

 viduals were placed in a dish with several males 

 which were recently torn from females. The muti- 

 lated males were soon seized and carried about as 



