20 THE EVOLUTION OF SEX. 



From the presupposition, then, of the intimate connection between 

 the sexuality and the secondary characters (which is indeed every- 

 where allowed), it is possible to advance a step further. Thus in 

 regard to color, that the male is usually brighter than the female is an 

 acknowledged fact. But pigments of many kinds are physiologically 

 regarded as of the nature of waste products. Such, for instance, is 

 the sruanin, so abundant on the skin of fishes and some other animals. 

 Abundance of such pigments, and richness of variety in related series, 

 point to preeminent activity of chemical processes in the animals which 

 possess them. Technically expressed, abundant pigments are express- 

 ions of intense metabolism. But predominant activity has been already 

 seen to be characteristic of the male sex; these bright colors, then, 

 are often natural to maleness. In a literal sense animals put on beauty 

 for ashes, and the males more so because they are males, and not 

 primarily for any other reason whatever. We are well aware that, in 

 spite of the researches of Krukenberg, Sorby, Macmunn, and others, 

 our knowledge of the physiology of many of the pigments is still very 

 scanty. Yet in many cases, alike among plants and animals, pigments 

 are expressions of disruptive process, and are of the nature of waste 

 products; and this general fact is at present sufficient for our conten- 

 tion, that bright coloring 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 con- 

 nected 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 Mbbius 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 dis- 

 ease in higher forms. To free itself from the irritant pressure of this 

 secretion, the male rubs itself against external objects, — most con- 

 veniently upon its nest. Thus the curious weaving instinct does not 

 demand or find rationale in the cumulative action of natural selection 



