380 TEE DESCENT OF MAN. 



so frequently occurs with secondary sexual characters, both 

 sexes of some species of rays (for instance R. batis), when 

 adult, possess sharp, pointed teeth; and here a character, 

 proper to and primarily gained by the male, appears to have 

 been transmitted to the offspring of both sexes. The teeth 

 are likewise pointed in both sexes of R. maculata, but only 

 when quite adult; the males acquiring them at an earlier 

 age than the females. We shall hereafter meet with anal- 

 ogous cases in certain birds, in which the male acquires the 

 plumage common to both sexes when adult, at a somewhat 

 earlier age than does the female. With other species of 

 rays the males even when old never possess sharp teeth, and 

 consequently the adults of both sexes are provided with 

 broad, flat teeth like those of the young, and like those of 

 the mature females of the above-mentioned species.* As 

 the rays are bold, strong and voracious fish, we may suspect 

 that the males require their sharp teeth for fighting with 

 their rivals; but as they possess many parts modified and 

 adapted for the prehension of the female, it is possible that 

 their teeth may be used for this purpose. 



In regard to size, M. Car onnierf maintains that the 

 female of almost all fishes is larger than the male; and Dr. 

 Giinther does not know of a single instance in which the 

 male is actually larger than the female. With some 

 Cyprinodonts the male is not even half as large. As in 

 many kinds of fishes the males habitually fight together, it 

 is surprising that they have not generally become larger 

 and stronger than the females through the effects of sexual 

 selection. The males suffer from their small size, for, 

 according to M. Carbonnier, they- are liable to be devoured 

 by the females of their own species when carnivorous, and 

 no doubt by other species. Increased size must be in some 

 manner of more importance to the females than strength 

 and size are to the males for fighting with other males; 

 and this perhaps is to allow of the production of a vast 

 number of ova. 



In many species the male alone is ornamented with 

 bright colors; or these are much brighter in the male than 

 the female. The male, also, is sometimes provided with 



* See Yarrell's account of the rays in his " Hist, of British Fishes,'' 

 vol. ii, 1836, p. 416, with an excellent figure, and pp. 423, 432. 



f As quoted in " The Farmer," 1868, p. 369. 



