336 THE DESCENT OF MAN. 



strange monster, the Chimaera monstrosa, the male has a hook- 

 shaped bone on the top of the head, directed forwards, with its 

 end rounded and covered with sharp spines; in the female "this 

 "crown is altogether absent," but v/hat its use may be to the male 

 is utterly unknown." 



The structures as yet referred to are permanent in the male 

 after he has arrived at maturity; but with some Blennies, 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 temporary 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 provided. In many of the Chromidae, for 

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

 hear from Professor Agassiz,^^ 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 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 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 color from the fe- 

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

 This is likewise the case '.vith a multitude 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 black-fish. "-'^ An anal- 

 ogous and even greater change takes place with the Salmo eriox 

 or bull trout; the males of the char (S. umbla) are likewise at 



" p. Buckland, in 'I.and and Water,' July, 1868, p. 377, with a figure. 

 Many other cases could be added of structures peculiar to the male, 

 of which the uses are not known. 



2» 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 Fishes,' vol. i, 1836, pp. 10, 12, 35. 



