T24 CHORDATE ANATOMY 



tion of epidermis and corium, and is usually excessively pigmented. When 

 a mole is congenital and involves blood capillaries, it forms a "birthmark." 



Since pigments like those of vertebrates are found also in invertebrates, 

 there is no reason to question their common origin. Many animals 

 below the mammals have their pigments in special cells, the chromato- 

 phores, which "expand" or "contract" (see page loi) under the influence 

 of hormones and thus alter the color of the skin. The colors of lizards, 

 which are often brilliant, are not in their scales, but in chromatophores 

 of the underlying corium. 



Widely among vertebrates, pigments of scales, skin, hair, or feathers 

 often show striking and elaborate patterns that serve for protection, 

 warning, recognition, or sexual allure; but in man chiefly the region of the 

 nipples and the external genitals are slightly darker than the rest of the 

 body. In man and some other hairless mammals, such as the elephant, 

 the function of the skin pigment is to check ultraviolet light before it 

 penetrates to living cells. Everyone has observed the effect of the sun's 

 rays upon unwonted skin, and the promptness with which the skin 

 responds by tanning. Lacking skin pigment, men could not live in some 

 parts of the earth. 



Color in Races and Individuals. The blue of the iris of human children 

 and new-born kittens is an interference color, like the blue of the sky or 

 the "eyes" of a peacock's tail. Later, as the iris fibers thicken, the inter- 

 ference is less perfect, and the eye is gray. Brown pigment in some fibers 

 only, gives hazel. Brown eyes are evenly pigmented. Dark brown eyes 

 are called black. 



There is also the yellow pigment which, nearly free from brown, gives 

 the amber eyes of some blondes. The same color intensified makes the 

 red iris that sometimes accompanies red hair. The interference blue 

 slightly masked by yellow, gives that rarest of all eye colors, green. 



In general, among Europeans, the eyes are less pigmented than the 

 hair, so that dark hair with gray-blue eyes is common. But some blondes 

 have a striking color scheme, eyes darker than the hair. 



Hair is colored by the same two pigments, both usually present, with 

 the brown-black, masking the red-yellow, except in strong light. But 

 some dark hair lacks the red and is blue-black. 



Some blondes have no brown pigment, and little yellow. Most have 

 brown also, along with varying amounts of yellow. The tow head with 

 a touch of dark, is the ash blond. Yellow with some red is golden; and 

 starting from this, the red may strengthen to a rather unadmired carrot 

 or orange. More brown carries the red over into auburn; still more gives 

 bronze. 



Hair that has lost its pigment is white, for the same reason that 

 snow is; the crystal faces of the one and the cell walls of the other scatter 

 the light. 



