458 THE BIOLOGICAL BASIS OF INDIVIDUALITY 



individual peculiarities, such as the color of hair and of iris, the cephalic 

 index, or similar characteristics, which, all combined, represent the mosaic 

 structure of the organism, in contrast to the essential individuality, which is 

 based on the organismal differentials. However, while many persons have 

 brown hair or blue eyes, the pattern of the skin ridges, as stated, is specific 

 in every individual. The ridge patterns of the skin, together with other mosaic 

 characters, differ as to the frequency with which certain peculiarities are 

 present in different races, the difference between races being, therefore, 

 largely statistical, the same structural elements as a rule occurring in all of 

 them. The papillary skin patterns have this statistical characteristic in 

 common also with the factors on which blood grouping depends, certain 

 blood groups being found more often in some races than in others. But, like 

 the individuality differentials, the skin patterns represent individual character- 

 istics, while the features distinguishing the four original blood groups do not, 

 to the same degree, allow the differentiation of individuals; they represent 

 group characters, as their name implies. 



In the case of monkeys, the parts of the skin where these ridges are found 

 serve as instruments with which to hold fast to trunks of trees and other 

 objects of a similar character, and those types of ridges which may be of use 

 in this function have been designated as "friction ridges." According to the 

 description given by Wilder and Wentworth, the ridges run, in general, in an 

 approximately parallel direction over the greater part of the friction skin, 

 more or less across the longitudinal axes of hand and foot, but in certain 

 definite places where the surface rises slightly, to come into fuller contact 

 with external objects, there occur some departures from the usual course 

 and the ridges form loops, typical concentric whorls and spiral whorls or 

 spirals. These patterns are arranged about a central core which corresponds 

 to the center or summit of the mound. At the point of origin of certain ridges 

 of the patterns, formations may be found which resemble the letter delta and 

 are therefore called "deltas." In addition there are distinguished some ridges 

 which connect the bases of adjoining whorls, and according to the mode in 

 which these ridges end, they are designated as inner and outer melting 

 whorls. Furthermore, there can be recognized the socalled "details" first 

 described by Galton : the forks, ends, islands and enclosures, signifying the 

 length and shape of certain interrupted portions of ridges. 



Pairs of symmetric fingers in both hands may have their own peculiarities. 

 In one finger pair one pattern may predominate, and in another pair, another 

 pattern. The number of ridges may differ in certain areas of the skin in 

 different individuals, and this quantitative factor behaves in a corresponding 

 manner in each finger pair in the same individual. Taking all these peculiari- 

 ties together, it is impossible to duplicate the character even of a relatively 

 small area of friction skin in two individuals. The ridges are a permanent 

 bodily mark, never changing throughout life; they originate in the embryo 

 and even after injury they form again in the same manner, unless the injury 

 has led to the destruction of the entire epidermis over a given area. 



As stated above, the average frequency with which certain patterns occur 



