THE BREEDING SEASON 29 



former size, but still present for some time a distinctive ap- 

 pearance owing to their being crowded with black pigment-cells. 

 Whatever may be the precise purpose of this curious modifi- 

 cation it is certain that its development is associated with 

 reproductive activity, and so may be regarded as an expression 

 of the intense vitality which the organism exhibits at this period. 



Some animals exhibit in the breeding season a particularly 

 vivid coloration which is absent from them at other times. The 

 case of the male dragonet (Callionymus lyra), which becomes a 

 brilliant blue-and-yellow colour, has been discussed at some 

 length by Cunningham, 1 who concludes that the production of 

 the guanin and pigment that give rise to the colour is to be 

 connected with the intense nervous excitement which affects the 

 fish at the time of courtship. " Physiological processes are 

 known to be governed largely by nervous impulses, and not 

 merely the circulation, but the excretory activity of the skin, 

 are known to be influenced by nervous action. Pigment and 

 guanin are produced in the skin by the secretory or excretory 

 activity of the living cells." 2 Whatever be the precise ex- 

 planation of this particular instance of intenser coloration, 

 there can be no doubt that it is an indication of a more active 

 metabolism. 



The brilliant colours of the male lump-sucker (Cydopterus 

 lumpus), and of other fish 3 at the time of breeding, are probably 

 due to the same causes as in the dragonet. 4 



1 Cunningham (J. T.), loc. cit. 2 Cunningham (J. T.), loc. cit. 



3 Numerous instances are given by Darwin, loc. cit., both for fishes and 

 Amphibians. 



4 The nuptial changes which occur in fishes are not necessarily in the 

 direction of increased brilliance of coloration. Miss Newbigin describes 

 these changes in the salmon as follows: "When the fish comes from the 

 sea the skin is of a bright silvery hue, while the flesh has the familiar 

 strong pink colour. The small ovaries are of a yellow-brown colour. As 

 the reproductive organs develop during the passage up the river, certain 

 definite colour-changes occur. The skin loses its bright silvery colour, and, 

 more especially in the male, becomes a ruddy-brown hue. At the same time 

 the flesh becomes paler and paler, and in the female the rapidly growing 

 ovaries acquire a fine orange-red colour. The testes in the male remain a 

 creamy white. After spawning the skin tends, in both sexes, to lose its ruddy 

 colour and to regain the bright silvery tint ; the flesh, however, remains pale 

 until the kelt has revisited the sea" (Report of Scottish Fishery Board, 1898). 



Barrett-Hamilton (Proc. Camb. Phil. Soc., vol. x., 1900, and Annals and 



