262 THE COURTSHIP OF ANIMALS 



the need of some exceptional means whereby the males 

 may discover the whereabouts of the females, while in 

 the case of the swarming hosts formed by Water-fleas 

 and Brine-shrimps, for example, no such highly special- 

 ized aid is necessary. Instead, the males have developed 

 powerful arms for the capture and retention of the females. 

 In the case of the Brine-shrimp these arms are of quite 

 formidable proportions. The males of the Copepoda, 

 remarks Weismann, " possess on their anterior antennae 

 an arrangement which enables them to throw a long, 

 whip-like structure like a lasso round the head of the 

 female as she rapidly swims away. The antennas of 

 the male Daphnids, too, are in one genus (Moina) 

 developed into a grasping apparatus ; . . . the first 

 antennae . . . are not only much longer and stronger 

 than those of the female, but they are also armed with 

 claws at the end, so that the males can catch their mates 

 as with a fork, and hold them fast. And even that was 

 not enough, for, in addition, the males of most Daphnids 

 possess a sickle-shaped but blunt claw on the first pair 

 of legs, which enables them to cHng to the smooth shell 

 of the female, and to clamber up on to it to get into the 

 proper position for copulation. 



" If we inquire into the manner of the origin of secondary 

 sexual characters of this kind, we shall find that both 

 may have been increased by sexual selection, for a male 

 with a better sickle will succeed more quickly in getting 

 into the proper position for copulation than one with a 

 less perfect mechanism. This assumption does not rest 

 on mere theory, for I was once able ... to observe for 

 a considerable time, under the microscope, a female to 

 whose shell two males were clinging, each trying to push 

 the other off. Nevertheless, it seems to me very question- 



