SEX RECOGNITION AMONG AMPHIPODS. 289 



pleopods when the body is strongly bent upon itself serves only 

 to keep a current of water passing by the gills. She is carried 

 about like a helpless burden, allowing her vigorous spouse to 

 assume the entire labor of transportation and the responsibility 

 of keeping her as well as himself out of danger. The efforts of 

 the male to seize the female and get her into the proper position 

 to be carried have the effect of inducing her to throw herself into 

 the characteristic bodily attitude and remain quiet. The attitude 

 assumed by the female is similar to that observed in the ordinary 

 thigmotactic reaction of amphipods and may, perhaps, be but the 

 same form of response, somewhat modified and specialized in re- 

 lation to the function of reproduction. When the males are torn 

 away from the females they soon seize their partners again and 

 roll them about into the proper position and then proceed on 

 their way in apparent contentment. The female as soon as seized 

 by the male curls up and allows herself to be rolled and tumbled 

 about without a show of resistance or protest. The males, as a 

 rule, are considerably larger than the females and usually get 

 their partners into the desired position quite readily ; but when a 

 small male attempts to carry a large female he experiences much 

 difficulty. I have observed a male Hyalella endeavoring to carry 

 a female somewhat larger than himself. After seizing the female 

 he would turn her around until she finally came into the proper 

 position for transportation, but owing to the larger size of his 

 partner the male could not reach around her body so as to carry 

 her away. No sooner was the female properly adjusted than the 

 male would lose hold of her round body and the same efforts 

 had to be repeated. During all this performance the female re- 

 mained dutifully passive. After watching the further struggles 

 of the male for over half an hour I became convinced, although 

 he was not, that he had undertaken an impossible task, and dis- 

 continued my observations. 



In order to ascertain if sight plays any part in sex recognition 

 in Hyalella, I tore some males away from their partners, 

 blackened their eyes with asphalt varnish, and placed them in a 

 dish with several females. It was not long before each of the 

 blinded males was provided with a mate. Sight, therefore, is 

 not the determining factor in sex recognition in this species. 



