320 SEXUAL SELECTION. [Pai>.t II, 



thinks not more than may be accounted for by their dif- 

 ferent habits of life, such as by the male wandering 

 more about and being thus more exposed to the light. 

 In a curious Bornean crab, which inhabits sponges. Mi*. 

 Bate could always distinguish the sexes by the male not 

 having the ejndermis so much rubbed off. Dr. Power 

 tried to distinguish by color the sexes of the species 

 which inhabit the I\rauritius, but always failed, except 

 with one sj^ecies of Squilla, proably the JS. stylifera^ the 

 male of which is described as being " of a beautiful blu- 

 ish-green," with some of the appendages cherry-red, while 

 the female is clouded with brown and gray, " with the 

 red about her much less vivid than in the male."" In this 

 case, we may suspect the agency of sexual selection. With 

 Saphirina (an oceanic genus of Entomostraca, and there- 

 fore low in the scale) the males are furnished with minute 

 shields or cell-like bodies, which exhibit beautiful chan- 

 ging colors ; these being absent in the females, and in the 

 case of one species in both sexes." It Avould, however, be 

 extremely rash to conclude that these curious organs serve 

 merely to attract the females. In the female of a Brazil- 

 ian species of Gelasimus, the v.hole body, as I am informed 

 by Fritz Mtiller, is of a nearly uniform grayish-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 colors 

 are liable to change in the course of a few minutes — the 

 white becoming dirty-gray or even black, the green " los- 

 ing much of its brilliancy." The males apparently are 

 much more numerous than the females. It deserves es- 

 pecial notice that they do not acquire their bright colors 

 until they become mature. They differ also from the fe- 



'" Mr. Ch. Frascr, in 'Proc. Zoolog. Soc' 18G9, p. 3. I am indebted 

 to Mr. Bate for the statement from Dr. Power. 



" Clans, 'Die freilebenden roi)epoden,' 1863, ?. 35. 



