34° The Descent of Man. Paet IL 



neitlier sex is thus provided. In many of the Chromidae, foi 

 instance in Geophagus and especially in Cichla, the males, as I 

 hear from Professor Agassiz, 21 have a conspicuous protuberance 

 on the forehead, which is wholly wanting in the females and in 

 the young males. Professor Agassiz adds, " I have often 

 " observed these fishes at the time of spawning when the pro- 

 '* tuberance is largest, and at other seasons when it is totally 

 " wanting, and the two sexes shew no difference whatever in the 

 " outline of the profile of the head. I never could ascertain that 

 v it subserves any special function, and the Indians on the 

 %s Amazon know nothing about its use." These protuberances 

 resemble, in their periodical appearance, the fleshy caruncles on 

 the heads of certain birds ; but whether they serve as ornaments 

 must remain at present doubtful. 



I hear from Professor Agassiz and Dr. Giinther, that the males 

 of those fishes, which differ permanently in colour from the 

 females, often become more brilliant during the breeding-season. 

 This is likewise the case with a multitude of fishes, the sexes of 

 which are identical in colour at all other seasons of the year. 

 The tench, roach, and perch may be given as instances. The 

 male salmon at this season is "marked on the cheeks with 

 " orange-coloured stripes, which give it the appearance of a 

 " Labrus, and the body partakes of a golden orange tinge. The 

 " females are dark in colour, and are commonly called black- 

 " fish." 22 An analogous and even greater change takes place 

 with the Salmo eriox or bull trout ; the males of the char 

 (S. umhhi) are likewise at this season rather brighter in colour 

 than the females. 23 The colours of the pike (Esox reticulatus) of 

 the United States, especially of the male, become, during the 

 breeding-season, exceedingly intense, brilliant, and iridescent. 24 

 Another striking instance out of many is afforded by the male 

 stickleback (Gasterosteits leiurus), which is described by Mr. 

 Warington, 25 as being then "beautiful beyond description." 

 The back and eyes of the female are simply brown, and the belly 

 white. The eyes of the male, on the other hand, are " of the 

 " most splendid green, having a metallic lustre like the green 

 "■ feathers of some humming-birds. The throat and belly are 

 " of a bright crimson, the back of an ashy-preen, and the whole 

 " fish appears as though it were somewhat translucent and 



21 See also 'A Journey in Brazil,' Mag. of Nat. History,' vol. vi. 1841, 



by Prof, and Mrs. Agassiz, 1868, p. p. 440. 



220. 2 * ' The American Agriculturist,' 



28 Yarrell, 'British Fishes,' vol. 1868, p. 100. 



li. 1836, pp. 10, 12, 35. 25 ' Annals and Mag. of N T at. Hist* 



83 W. Thompson, in ' Annals and Oct. 1852. 



