26 THE PHYSIOLOGY OF REPRODUCTION 



the new growth is not completed until July or August in the 

 following year. 1 



A secondary sexual character of a comparable kind occurs in the 

 male salmon, in which the tip of the lower jaw, during the breeding 

 season, is turned up and enlarged, as if to protect the fish in fighting 

 when charged by another male. 2 



In Polypterus, during the breeding season, the anal fin of the male 

 becomes greatly enlarged and thickened, and has its surface thrown 

 into folds between the fin-rays. The object of this modification is 

 not known. 3 



The papillre on the hind limbs of the breeding male Lepidosiren 

 are structures which seem to possess a special significance, since 

 Kerr 4 has shown that they probably serve as accessory organs of 

 respiration. During the greater part of the year they are relatively 

 inconspicuous ; but as soon as the animal is set free at the beginning 

 of the wet season, they begin to grow with remarkable rapidity, 

 forming slender filaments tw y o or three inches in length and blood- 

 red in colour from their intense vascularity. After the breeding 

 season is over the filaments commence to atrophy, and eventually 

 shrink to their former size, but still present for some time a 

 distinctive appearance owing to their being crowded with black 

 pigment-cells. Whatever may be the precise purpose of this curious 

 modification 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 1 a brilliant 

 blue-and-yellow colour, has been discussed at some length by 

 Cunningham, 5 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." 6 Whatever 

 be the precise explanation of this particular instance of intenser 

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

 active metabolism. 



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



2 Darwin, Descent of Man, Popular Edition, London, 1901. 



3 Budgett, loc. cit. 4 Kerr, loc. cit. 



" Cunningham (J. T,), loc. cit. 6 Cunningham (J. T.), loc. cit. 



