336 SEXUAL SELECTION. Part II. 



minute shields or cell-like bodies, which exhibit beau- 

 tiful changing colours ; these being absent in the 

 females, and in the case of one species in both sexes. 11 

 It would, however, be extremely rash to conclude that 

 these curious organs serve merelv to attract the females. 



© Ml 



In the female of a Brazilian species of Gelasimus, the 

 whole body, as I am informed by Fritz Muller, is of a 

 nearly uniform greyish-brown. In the male the posterior 

 part of the cephalo-thorax is pure white, with the 

 anterior part of a rich green, shading into dark brown ; 

 and it is remarkable that these colours are liable to 

 change in the course of a few minutes — the white 

 becoming dirty grey or even black, the green " losing 

 much of its brilliancy." The males apparently are 

 much more numerous than the females. It deserves 

 especial notice that they do not acquire their bright 

 colours until they become mature. They differ also 

 from the females in the larger size of their chela?. 

 In some species of the genus, probably in all, the 

 sexes pair and. inhabit the same burrow. They are 

 also, as we have seen, highly intelligent animals. 

 From these various considerations it seems highly 

 probable that the male in this species has become 

 srailv ornamented in order to attract or excite the 

 female. 



It has just been stated, that the male Gelasimus does 

 not acquire his conspicuous colours until mature and 

 nearly ready to breed. This seems the general rule in 

 the whole class with the many remarkable difference^ 

 in structure between the two sexes. We shall here- 

 after find the same law prevailing throughout the great 

 sub-kingdom of the Yertebrata, and in all cases it is 

 eminently distinctive of characters which have been 



11 Clans, ' Die freilebendeu Copepoden/ 1863, s. 35. 



