SEX RECOGNITION IN CYCLOPS. 



S. J. HOLMES. 



The sexual behavior of copepods presents several points of 

 similarity with that of the amphipods which was described by the 

 writer in a previous paper. 1 In both groups the males clasp and 

 swim about with the females for a long time previous to copula- 

 tion ; and in both groups the behavior of the female is much the 

 same while being clasped by the male. Having an opportunity 

 to study a thriving culture of Cyclops fimbriatus in which pairing 

 was actively going on the endeavor was made to ascertain if the 

 method of the sex recognition employed in the amphipods occurs 

 also in this species of a quite distantly related group. 



Male Cyclops, as is well known, have the first antennae en- 

 larged and modified to form a clasping organ. In Cyclops fim- 

 briatus the male usually clasps the female just in front of an 

 enlargement at the base of the abdomen. Females carrying eggs 

 are sometimes seized, and also females not more than half grown. 

 Males show great eagerness in grasping the females, and they 

 can be compelled to release their hold only with difficulty. They 

 may be poked about roughly with a needle and the posterior 

 part of the body may be cut off without causing them to leave 

 the female. I have often picked up pairs in a fine pipette and 

 forcibly squirted them out several times without succeeding in 

 separating the two sexes. 



As the pairs of Cyclops swim through the water the males are 

 usually the more active. Frequently the female remains entirely 

 quiet with the appendages drawn close to the body, and the body 

 flexed vertrally, allowing herself to be passively carried about 

 by her mate. At other times the female may swim as actively 

 as the male. In general the behavior of the females and their 

 attitude while being carried closely resemble what is found among 

 the Amphipoda. So also does their behavior when the males 

 come in contact with them and attempt to seize them. The 



1 BIOLOGICAL BULLETIN, Vol. 5, 1903. 



313 



