24 THE EVOLUTION OF SEX. 



plants and animals, pigments are expressions of disruptive 

 processes, and are of the nature of waste products ; and this 

 general fact is at present sufficient for our contention, that bright 

 colouring or rich pigmenting is commonly a natural expression of 

 the male constitution. For the red pigment so abundant in 

 the female cochineal insect, which appears to be of the nature 

 of a reserve and not a waste product, and for similar occurrences, 

 due exception must be made. 



In the same way, the skin eruptions of male fishes at the 

 spawning season seem more pathological than decorative, and 

 may be directly connected with the sexual excitement. One 

 instance of the way in which the reproductive maturity is known 

 to effect a by no means obviously related result may be given. 

 Every field naturalist knows that the male stickleback builds a 

 nest among the weeds, and that he weaves the material together 

 by mucous threads secreted from the kidneys. The little animal 

 is also known to have strong passions ; it is polygamous in 

 relation to its mates, and most pugnacious in relation to its 

 rivals. Professor Mobius has shown that the male reproductive 

 organs (or testes) become very large at the breeding season, and 

 that they press in an abnormal way upon the kidneys. This 

 encroachment produces a pathological condition in the kidneys, 

 and the result is the formation of a mucous secretion, somewhat 

 similar to what occurs in renal disease in higher forms. To 

 free itself from the irritant pressure of this secretion, the male 

 rubs itself against external objects, most conveniently upon its 

 nest. Thus the curious weaving instinct does not demand or 

 find rationale in the cumulative action of natural selection upon 

 an inexplicable variation, and is traced back to a pathological and 

 mechanical origin in the emphatic maleness of the organism. 

 The line of variation being thus given, it is of course conceiv- 

 able that natural selection may have accelerated it. 



So too, though again the physiological details are scanty, the 

 superabundant growth of hair and feathers may be interpreted, 

 in some measure through getting rid of waste products, for we 

 shall see later how local katabolism favours cell multiplication. 

 Combs, wattles, and skin excrescences point to a predominance 

 of circulation in the skin of the feverish males, whose tempera- 

 tures are known in some cases to be decidedly higher than 

 those of the females. Even skeletal weapons like antlers may 

 be similarly interpreted : while the exaggerated activity of the 

 scent-glands is another expedient for excreting waste. 



