THE INTEGUMENTARY SYSTEM 12 5 



Skin color is like hair color except that the blood color below the pig- 

 ment may show through, and that sunUght, which fades the Hfeless hair, 

 stimulates the living skin to turn dark. 



Primitive man was dark as the ape ancestor was, and as most races 

 are still. Reducing the black pigment, with the yellow retained, gives 

 the Mongolian skin color. The stronger yellow, together with a good 

 deal of brown, is the traditional hue of the Red Man, though as a matter 

 of fact, most Indians are brown, like most White Men. 



The blond White Man is a local race that originated in some region 

 near the Baltic, apparently since the last Ice Age. Being highly energetic 

 and uncommonly well endowed, the descendants of these blond giants 

 have made their way all over the world, and, much diluted with darker 

 blood, still appear in most civilized countries of the world. 



Why their blondness, nobody knows. It cannot be due to chmate, 

 for the Eskimos, Samoyads of Siberia, the Patagonians, and the people 

 of northern China are all dark. Naturally, a blond race could hardly 

 survive in the tropics; but a white skin is no obvious advantage anywhere. 

 Yet certain studies of Chicago children show that the highly pigmented 

 Italians are more Uable than lighter stocks to rickets, which is a sunlight- 

 deficiency disease. So it may be that in high latitudes, in a wooded coun- 

 try or one that has much cloud and fog, a fair skin that is still able to tan 

 may have a selective value and be accounted for on Darwinian principles. 



Skin color plays queer tricks. Any two parents, even two Negroes, 

 may have an albino child; two dark-haired parents may somehow miss 

 with the brown pigment and have red-haired offspring. The most that 

 anyone can say is that "Nordic" man probably began as a mutant from 

 a dark stock. Possibly, after the mutation appeared, it was admired and 

 selective mating kept it to the fore. 



CUTANEOUS GLANDS 



Since among invertebrates most glands are unicellular, it has generally 

 been assumed that the multicellular glands of vertebrates have evolved 

 from such beginnings, an increase in the size of the secreting cells tending 

 to carry them into the underlying corium, where groups of such 

 epidermal cells become multicellular organs. 



Be this as it may, cutaneous glands develop, much as hairs do, from 

 solid cords, which are proliferated from the stratum germinativum and 

 grow downward into the underlying corium. The lumen of the gland 

 forms later, to connect with the exterior, and the gland anlage differen- 

 tiates into a secretory portion and a lining for the duct. The secretory 

 cells become intimately associated with blood-vessels and nerves. 



Sweat Glands. In man sweat glands occur in most regions of the 

 body, and are especially abundant on the palms and soles. They are, 

 for the most part, of the simple tubular type, much coiled to increase the 



