THE INTEGUMENT AND THE EXOSKELETON 119 



The pigment of vertebrate integument is usually contained 

 in branching connective tissue cells, produced in the corium, 

 but capable of wandering into the epidermis. In some cases, 

 as in Man and monkeys, the stratum germinativum of the epi- 

 dermis is pigmented, and varying degrees of this are respon- 

 sible for the great variety of skin color in Man. Although 

 the connection is hard to prove, it is a general truth that 

 human races that live in the tropics are the darkest and that 

 the skin grows gradually paler in races nearing the poles, 

 there being a correlation in this respect between skin color and 

 hair color. As instances of this, there may be recalled the sooty 

 blackness of the Sudanese, and the dark color of the aborigi- 

 nes of India, which may be compared with the lighter color 

 of Europeans and northern Asiatics. More convincing cases 

 of this are seen in representatives of the same race ; such as is 

 shown by the contrast between the Italians and Spaniards on 

 the one hand and the Scandinavians on the other, or between 

 the American Indians in Canada and those in Mexico. A 

 similar reduction in pigment is found in people living at high 

 altitudes in comparison with the same race living in the bor- 

 dering lowlands. The importance of these correlations has 

 been repeatedly denied, and there are numerous instances of 

 exceptions, often conspicuous ones like the dark skin and hair 

 of the Eskimo, and at the present state of our knowledge too 

 much cannot be urged on this point. 



Another point of interest lies in the regions of the body in 

 which the pigmentation is the densest. As a general rule it 

 may be observed, not in vertebrates alone but in invertebrates 

 as well, that the darkest and most deeply colored parts are 

 those that lie uppermost, exposed to the light, while the under 

 parts are lacking in pigment. That this bears no relation to 

 the architecture of the body may be seen in the case of the 

 flounder, a fish that is much compressed laterally and has the 

 habit of lying upon one side at the bottom in rather shallow 

 water. This habitual lower side, which is sometimes the left, 

 sometimes the right, half of the body, is entirely colorless, 

 while the upper side is marked with a complicated pattern 



