342 The Descent of Man. P^ ut I r. 



males of which hatch their eggs in their mouths ; and tho?e who 

 do not believe in the principle of gradual evolution might ask how 

 could such a habit have originated ; but the difficulty is much 

 diminished when we know that there are fishes which thus 

 collect and carry the eggs ; for if delayed by any cause in 

 depositing them, the habit of hatching them in their mouths 

 might have been acquired. 



To return to our more immediate subject. The case stands 

 thus : female fishes, as far as I can learn, never willingly spawn 

 except in the presence of the males ; and the males never fertilise 

 the ova except in the presence of the females. The males fight 

 for the possession of the females. In many species, the males 

 whilst young resemble the females in colour ; but when adult 

 become much more brilliant, and retain their colours throughout 

 life. In other species the males become brighter than the females 

 and otherwise more highly ornamented, only during the season 

 of love. The males sedulously court the females, and in one 

 case, as we have seen, take pains in displaying their beauty 

 before them. Can it be believed that they would thus act to no 

 purpose during their courtship ? And this would be the case, 

 unless the females exert some choice and select those males 

 which please or excite them most. If the female exerts such 

 choice, all the above facts on the ornamentation of the males 

 become at once intelligible by the aid of sexual selection. 



We have next to enquire whether this view of the bright 

 colours of certain male fishes having been acquired through 

 sexual selection can, through the law of the equal transmission of 

 characters to both sexes, be extended to those groups in which the 

 males and females are brilliant in the same, or nearly the same 

 degree and manner. In such a genus as Labrus, which includes 

 some of the most splendid fishes in the world — for instance, the 

 Peacock Labrus (L. pavo), described, 28 with pardonable exaggera- 

 tion, as formed of polished scales of gold, encrusting lapis-lazuli, 

 rubies, sapphires, emeralds, and amethysts — we may, with much 

 probability, accept this belief; for we have seen that the sexes in 

 at least one species of the genus differ greatly in colour. "With 

 some fishes, as with many of the lowest animals, splendid colours 

 may be the direct result of the nature of their tissues and of the 

 surrounding conditions, without the aid of selection of any kind. 

 The gold-fish (Cyprinus auratus), judging from the analogy of 

 the golden variety of the common carp, is perhaps a ca?e in point, 

 as it may owe its splendid colours to a single abrupt variation, 

 due to the conditions to which this fish has been subjected under 



28 Bor7 de Saint Vincert, in ' Diet. Class. d'Hist. Nat.' torn. ix. 1826 

 p. 151. 



