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- 
midm, for instance in Geophagus and especially in Cichla, 
tlie 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 breeding-season. This is likewise the case with a 
multitude of fishes, the sexes of 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 
See also ‘ A Journey in Brazil/ by Prof, and Mrs. xVgassiz, 1868, 
p 220. 
