SEX RECOGNITION AMONG AMPHIPODS. 1 



S. J. HOLMES. 



How do males of the amphipod Crustacea distinguish the 

 females ? It is well known that the males of the Gammaridea have 

 the curious habit of carrying the females under their body for a 

 considerable time. This act of transportation has probably no 

 further significance in relation to the fertilization of the eggs than 

 to secure the proximity of the two sexes when the proper time 

 for fertilization arrives. According to the observations of Delia 

 Valle on Gainniarus pungcns the eggs are not fertilized until after 

 they are laid, oviposition occurring a short time after moulting. 

 When the moulting of the female has been effected, the male 

 bends his body beneath that of his mate and deposits spermatozoa 

 upon the ventral surface of her thorax. The deposit of sperm is 

 followed within half an hour by the laying of the eggs. After 

 the act of copulation the male regains his original position and 

 swims about with the female as before. The same relation of 

 oviposition to moulting was found by Miss Langenbeck in Micro- 

 deutopus, the male leaving the female during her moulting proc- 

 ess but soon resuming his previous position when the moult was 

 completed. 



The instinct of the male amphipod to seize and retain hold of 

 the female is one of remarkable strength. The male retains his 

 hold, despite all efforts to dislodge him, with remarkable persist- 

 ence, and will still cling to the female after the posterior half of 

 his body has been cut away. My own observations on the sexual 

 behavior of amphipods relate mainly to three species, AuipJiitJwe 

 longiinana Smith, Hyalclla dcntata Smith and Gammarus fasciatus 

 Say. The sexual behavior of these three species is remarkably 

 similar, athough they belong to as many distinct families. The 

 female while being carried about keeps remarkably impassive. 

 Her thoracic legs are drawn up, the abdomen held strongly 

 flexed, the whole body assuming as compact a form as possible. 

 She takes little or no part in swimming ; the movement of the 



1 From the Zoological Laboratory of the University of Michigan, Ann Arbor, Mich. 



288 



