306 THE DESCENT OF MAN. 



tance of a foot; it then saw the three other shells lying 

 near, and, evidently thinking that they might likewise roll 

 in, carried them to the spot where it had laid the first. It 

 would, I think, be difficult to distinguish this act from one 

 performed by man by the aid of reason. 



Mr. Bate does not know of any well-marked case of dif- 

 ference of color in the two sexes of our British crustaceans, 

 in which respect the sexes of the higher animals so often 

 differ. In some cases, however, the males and females differ 

 slightly in tint, but Mr. Bate thinks not more than may be 

 accounted for by their different habits of life; such as by 

 the male wandering more about, and being thus more 

 exposed to the light. Dr. Power tried to distinguish by 

 color the sexes of the several species which inhabit the 

 Mauritius but failed, except with one species of Squilla, 

 probably 8. styUfera, the male of which is described as 

 being "of a beautiful bluish-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. From M. Berths observation on 

 Daphnia, when placed in a vessel illuminated by a prism, 

 we have reason to believe that even the lowest crustaceans 

 <3an distinguish colors. AVith Saphirina (an oceanic genus 

 of Entomostraca), the males are furnished with minute 

 shields or cell-like bodies, which exhibit beautiful changing 

 colors; these are absent in the females, and in both sexes 

 of one species. \ It would, however, be extremely rash to 

 conclude that these curious organs serve to attract the 

 females. I am informed by Fritz Miiller, that in the 

 female of a Brazilian species of Gelasimus the whole body 

 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 " losing much of its brilliancy." It 

 deserves especial notice that the males do not acquire their 

 bright colors until they become mature. They appear to 



*Mr. Ch. Eraser, in " Proc. Zoolog. Soc," 1869, p. 3. I am 

 indebted to Mr. Bate for Dr. Power's statement, 

 f Claus, "Die freilebenden Copepoden," 1863, s. 35, 



