SEXUAL SELECTION 357 



wHle watching a shore- crab (Grelasimus) making its hurrow, 

 threw some shells toward the hole. One rolled in, and three 

 other shells remained within a few inches of the mouth. 

 In about five minutes the crab brought out the shell which 

 had fallen in, and carried it away to the distance of a foot; 

 it then saw the three other shells lying near, and, evidently 

 thinking that theylnight likewise roll in, carried them to the 

 spot where it had laid the first. It would, I think, be diffi- 

 cult 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 

 difference of color in the two sexes of our British crusta- 

 ceans, 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 ,ihe 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 S. stylifera, 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 

 maleV " In this case we may suspect the agency of sexual 

 selection. From M. Bert's observations on Daphnia, when 

 placed in a vessel illuminated by a prism, we have reason 

 eo believe that even the lowest crustaceans can distinguish 

 colors. "With 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 



•6 Mr. Ch. Fraser, in "Proc. Zoolog. Soc," 1869, p. 3. I am indebted to 

 Mr. Bate for Dr. Power's statement. 



>6 Glaus, "Die fveilebenden Copepoden," 1863, s. 35. 



