Skin Changes. 109 



and often destructive activity of the reproductive 

 centres finds sympathetic expression in the cells of 

 the skin, and there, too, is a powerful, and some- 

 times destructive, activity observable. 



Scales, feathers, hair, nails, claws, teeth, horns, 

 hoofs, and nearly if not all excretory glands, such 

 as the perspiratory and sebaceous, are outgrowths 

 of the skin. Hence, in them we find marked 

 changes, often riotous growths expressing their 

 superabundant vitality. 



Bearing in mind the tendency of the skin to 

 change, it is not difficult to understand the increased 

 brilliancy of color which is a general characteristic 

 of the breeding season. 



In certain species of fish the skin undergoes 

 changes which cause it to glow with quite re- 

 markable splendor, some acquiring a livery vying 

 in brilliancy with that worn by the butterflies 

 and beetles. 



The bare places or callosities on the baboon glow 

 with brilliant colors during reproductive activity. 



The feathers of birds, being direct outgrowths 

 of the skin, at the breeding season, grow more 

 «//w-looking, glossier and brighter. The male 

 bird, his cells being perhaps always more active 

 than those of the female, assumes a brighter 

 garb than she wears, unless some special cause 

 steps in to render it otherwise. 



In many forms of life, color changes herald the 

 advent of the reproductive period. 



