12 SEXUAL SELECTION. [Part IL 



that stiff hairs and flexible filaments can be useful in any 

 ordinary way to the males alone. The Monacanthus 

 scopas, which was shown to me in the British Museum by 

 Dr. Gtinther, presents a nearly analogous case. The male 

 has a cluster of stiff, straight spines, like those of a comb, 

 on the sides of the tail ; and these in a specimen six inches 

 long were nearly an inch and a half in length ; the female 

 has on the same place a cluster of bristles, which may be 

 compared with those of a tooth-brush. In another species, 

 the M. peronii, the male has a brush like that possessed 

 by the female of the last species, while the sides of the 

 tail in the female are smooth. In some other species the 

 same part of the tail can be perceived to be a little rough- 

 ened in the male and perfectly smooth in the female ; and 

 lastly, in others, both sexes have smooth sides. In that 

 strange monster, the Chimcera monstrosa, the male has a 

 hook-shaped bone on the top of the head, directed for- 

 ward, with its rounded end covered with sharp spines ; in 

 the female " this crown is altogether absent," but what its 

 use may be is utterly unknown. 17 



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 18 a crest is developed 

 on the head of the male only during the breeding-season, 

 and their bodies at the same time become 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 this case and in that of 

 the Monacanthus, we have good instances to how great 

 an extent the sexual characters of closely-allied forms may 



17 F. Buckland, in 'Land and Water,' July, 1868, p. 377, with a 

 figure. 



18 Dr. Gunther, 'Catalogue of Fishes,' vol. hi. pp. 221, 240. 



