2QO S. J. HOLMES. 



That the females are distinguished through the sense of smell 

 seemed more probable, since it has been shown that among 

 many insects sex recognition is brought about in this way. The 

 sense of smell in crustaceans is often highly developed and in 

 some groups probably affords the means by which the females 

 are distinguished. The sense of smell in the Crustacea is mainly, 

 although not quite exclusively, 1 located in the first antennae. To 

 determine if the male distinguishes the other sex by this sense, 

 recourse was had to the experiment which naturally suggested 

 itself, of removing the first antennae of several males and ob- 

 serving whether they experienced any difficulty in finding mates. 

 It was found that after they had recovered from the slight shock 

 of the operation, the males seized the females as eagerly as 

 before and carried them about in the usual manner. Even after 

 both pairs of antennse were removed the females were seized and 

 carried in the same way. It is very improbable, therefore, that 

 the sense of smell plays an important part in enabling male 

 Hyalellas to distinguish the other sex. The experiment was then 

 tried of placing several females in a small enclosure of wire gauze, 

 while several males which had recently been torn from females 

 were placed in the same dish, but outside of the enclosure. The 

 males paid not the slightest attention to the females within the 

 gauze ; but soon after the gauze was raised and the females 

 allowed to scatter through the dish most of the males had ac- 

 quired a partner. 



If one attentively observes Hyalellas as they are swimming 

 about, it will be seen that the males do not pursue the females, great 

 as their eagerness may be to seize and carry one of the opposite 

 sex. Only when the two sexes collide in their apparently random 

 movements does the male become aware of the presence of the 

 female. When a male and a female collide, the female curls up 

 and lies quiet while the male makes efforts to seize her. Should 

 two females 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 apparently attempts to seize 

 and carry the other, but as neither will consent to remain passive 

 they soon separate. The different reactions of the two sexes to 

 1 Bethe, Archiv. mic. Anat., Bd. 2, 1897 ; Holmes, BIOL. BULL., Vol. II., 1901. 



