FISHES. 331 



only during the breeding-season; but in the Salmo lycaodon of 

 N.-W. America the change, as Mr. J. K. Lord" believes, is perma- 

 nent, and best marked in the older males which have previously 

 ascended the rivers. In these old males the jaw becomes de- 

 veloped into an immense hook-like projection, and the teeth 

 grow into regular fangs, often more than half an inch in length. 

 With the European salmon, according to Mr. Lloyd," the tem- 

 porary hook-like structure serves to strengthen and protect the 

 jaws, when one male charges another with wonderful violence; 

 but the greatly developed teeth of the male American salmon 

 may be compared with the tusks of many male mammals, and 

 they indicate an offensive rather than a protective purpose. 



The salmon is not the only fish in which the teeth differ in 

 the two sexes; as this is the case with many rays. In the 

 thornback (Raia clavata) the adult male has sharp, pointed 

 teeth, directed backwards, whilst those of the female are broad 

 and flat, and form a pavement; so that these teeth differ in the 

 two sexes of the same species more than is usual in distinct 

 genera of the same family. The teeth of the male become sharp 

 only when he is adult; whilst young they are broad and flat 

 like those of the female. As so frequently occurs with secondary 

 sexual characters, both sexes of seme 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 analogous 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. Carbonnier^^ maintains that the female of 

 almost all fishes is larger than the male; and Dr. GUnther does 



8 'The Naturalist in Vancouver's Island,' vol. i. 1866, p. 54. 

 ' 'Scandinavian Adventures,' vol. 1. 1S54, pp. 100, 104. 

 •0 See Tarrell's account of the rays in his 'Hist, of British Fishes,' 

 vol. 11. 1S36, p. 416, with an excellent figure, and p. 422, 432. 

 " As quoted in 'The Parmer,' 1868, p. 369. 



