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erate. The segments of the pleon in this sex are coalesced, 

 their separate existence being indicated by the incisions at 

 the sides. The antennae are short and similar to those of 

 the female ; the legs are short bnt strong and clawed. The 

 eyes are very rudimentary in the females, but more de- 

 veloped in the males. 



Here we can obviously, in accounting for the difference 

 between the sexes, point to the fact that, whereas the female 

 is parasitic on the prawn, the male is parasitic on the female, 

 The latter, therefore, has a smaller supply of nourishment, 

 and all its functions are in abeyance, except those of holding 

 on to its support and fertilising the ova. In the female, on 

 the other hand, special parts are stimulated, and special 

 muscles are exercised in the support of the eggs and embryos, 

 which exercise, with the abundance of nourishment available, 

 are sufficient to account for her large size. It is somewhat 

 curious that the male, since, so far as we know, it does not 

 migrate from one female to another, should have more 

 developed eyes than the female, and yet it is not improbable 

 that in the act of fertilisation he is to some extent guided by 

 visual sensations, in which case the complete degeneration of 

 the eyes would be prevented. 



The young of Bopyrus, when they leave the incubatory 

 pouch, are much less degenerate than their parents, being 

 symmetrical and active. The second pair of antennae are 

 greatly elongated and form the principal organ of locomotion. 

 In the genus Gyge, members of which live on Galathea, the 

 body of the female is less asymmetrical than in Bopyrus, and 

 the male is slightly different in form, but the general 

 relations of male, female, and young are similar. 



In Hemiarthrus we have a more extraordinary form 

 which occurs in the branchial cavity of Hippolyte and 

 Pandalus. Towards one side the body is swollen out 

 into a globular mass distended with eggs, and the legs 



