442 THE DESCENT OF MAN 



nies, and in another allied genus," a crest is developed on 

 the head of the male only during the breeding season, and 

 the body at the same time becomes more brightly colored. 

 There can be little doubt that this crest serves as a tempo- 

 rary sexual ornament, for the female does not exhibit a trace 

 of it. In other species of the same genus both sexes possess 

 a crest, and in at least one species neither sex is thus pro- 

 vided. In many of the Chromidse, for instance in Geophagus 

 and especially in Gichla, the males, as I hear from Prof. 

 Agassiz," have a conspicuous protuberance on the forehead 

 which is wholly wanting in the females and in the young 

 males. Prof. Agassiz adds, "1 have often observed these 

 fishes 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 out- 

 line of the profile of the head. I never could ascertain that 

 it subserves any special function, and the Indians on the 

 Amasion know nothing about its use." These protuberances 

 resemble, in their periodical appearance, the fleshy caruncles 

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

 ornaments must remain at present doubtfuj. 



I hear from Prof. Agassiz and Dr. Gunther, that the 

 males of those fishes which differ permanently in color 

 from the females often become more brilliant during the 

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

 tude of fishes, the sexes of which are identical in color 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-colored stripes, which 

 give it the appearance of a Labrus, and the body partakes of 

 a golden orange tinge. The females are dark in color, and 

 are commonly called blackfish." " An analogous and even 

 greater change takes place with the Salmo eriox or bull trout; 

 the males of the char {^S. umbla) are likewise at this season 



"> Dr. Gunther, "Catalogue of Pishes," vol. iii. pp. 221 and 240. 



" See also "A Journey in Brazil," by Prof, and Mrs. Agassiz, 1868, p. 220. 



»* Tarrell, "British Kshes," vol. ii., 1836, pp. 10, 12, 36. 



