Chap. XII.] FISHES. 13 



differ. In many <>1" tlic Chromida?, for instance, in Geo- 

 phagus and esjK'cially in Cielila, the males, as I liear from 

 Prof. Agassiz,'" have a eonspieuons protuberance on the 

 forehead, which is wholly wanting in the females and in 

 the young males. Prof Agassiz adds : " I have often 

 observed these tislies at the time of spawning when the 

 protuberance is largest, and at other seasons when it is 

 totally wanting and the two sexes show no difference 

 whatever in the outline of the profile of the head. I never 

 could ascertain that it subserves any special function, and 

 the Indians on the Amazons know nothing about its use." 

 These protuberances in their periodical appearance resem- 

 ble the fleshy caruncles on the heads of certain birds ; 

 but whether they serve as ornaments must reniain at 

 present doubtful. 



The males of those fishes, which differ permanently in 

 color from the females, often become more brilliant, as I 

 hear from Prof. Agassiz and Dr. Gilnther, during the 

 breeding-season. This is likewise the case with a multi- 

 tude of fishes, the sexes of which at all other seasons of 

 the year are identical in color. The tench, roach, and 

 perch, may be given as instances. The male salmon at 

 this season is " marked on the cheeks with orange-colored 

 stripes, which gave it the a})i)earance of a Labrus, and 

 the body jiartakes of a golden-orange tinge. The females 

 arc (lark in color, and are commoidy called blackfish."" 

 An analogous and even greater change takes place with 

 the ^Sdlmo t'n'ojr^ or bull-trout ; the males of the char {S. 

 umblti) are likewise at this season rather brighter in 

 color than the females.^' The colors of the pike {Esox re- 



'» See also 'A .Tourney in Urazil,' by Prof. :in<l .Mrs. Agassiz, 1808, 

 p. 220. 



'» Yarrell, ' Hriti.^h Fishes,' vol. ii. 1S3C, pp. 10, 12, S;"). 



" W. Thompson, in 'Annals and Mag. of Nat. Ilistory,' vol. vi. 1811, 

 p. 440. 



