Chap. XII. FISHES. 13 



ing-season, and their bodies at the same time become 

 more brightly-coloured. 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 this 

 case and in that of the Monacanthus, we have good in- 

 stances to how great an extent the sexual characters of 

 closely-allied forms may differ. In many of the Chro- 

 midse, for instance in Geophagus and especially in Cichla, 

 the males, as I hear from Professor Agassiz,^^ have a con- 

 spicuous protuberance on the forehead, which is wholly 

 wanting in the females and in the young males. Pro- 

 fessor 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 shew 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 in their periodical appear- 

 ance resemble the fleshy caruncles on the heads of cer- 

 tain birds ; but whether they serve as ornaments must 

 remain at present doubtful. 



The males of those fishes, which differ permanently in 

 colour from the females, often become more brilliant, as 

 I hear from Professor Agassiz and Dr. Gunther, during 

 the breedimr-season. This is likewise the case with a 

 multitude of fishes, the sexes af which at all other 

 seasons of the year are identical in colour. The tench, 

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

 salmon at this season is " marked on the cheeks with 





^3 See also ' A Journey in Brazil,' by Prof, and Mrs. Agassiz, 1868, 

 p. 220. 



