( 309 ) 



foremost condition to obtain coi-rect notions concerning the pigmen- 

 tation of the skin is to understand proper!}^ the morphological 

 framework whereon the design is founded, and the manner in 

 which it is physiologically detei-mined. In endeavouring to elucidate 

 these questions, it becomes evident that the simple distinction between 

 •'design" in a narrower sense and "prime-colour", is not sufficient 

 for a rational description of the manifold pigmentations of the skin. 



According to my opinion, we ought at least to dislinguish three 

 elements, constituting in their complete or partial combination the 

 "design" in its widest acceptation. In order to obtain a proper 

 distinction between these three elements, it is necessary to introduce 

 a quantitative criterion into the problem. Besides the respective plus 

 and minus in the pigmentation, we shall therefore have to make still 

 another distinction, by opposing to the prime-colour respectively an 

 excedent and a defect contrast in the production of pigment. 



A few instances may suflice to elucidate this. In a white dog 

 with black ears black represents the contrasting colour just as white 

 does in a black horse with a white mark on its forehead. But in 

 the first case it may be called an excedent contrast, in the second 

 case a defect contrast. In an animal where the prevailing colour is 

 brown showing both black and white marks, we find combined the 

 three elements that ought to be distinguished : the brown prime- 

 colour, the excedent and the defect-contrasts. Starting from these 

 simple instances, we shall be able to compose a complete terminology, 

 by means of which the most important elements of the pigmentation 

 of the skin may be defined with tolerable exactness as to their shape, 

 extension and distribution. For instance the white mark on the fore- 

 head of the black horse we will call an isolated defect contrast. 

 Thus the dark stripes on neck and trunk of the zebra may be called 

 regular serial diagonal excedent contrasts, whilst the stripes on Galidictis 

 are regular serial longitudinal excedent contrasts. The morphological 

 and physiological basis for distinguishing between excedent and 

 defect-contrast, consists in the following points : 



1. In a large series of cases excedent-contrasts are found in such 

 places where the innervation of the skin is likewise strongest, whilst 

 on the contrary defect-contrasts are found in such places where this 

 innervation is feeblest. 2. We may observe that the excedent-contrasts 

 often correspond as to their shape and distribution with the carica- 

 tures of the dermatoma ^), whilst the defect contrasts often correspond 



1) G. Winkler and G. van Rmnberk, Structure and function of the trunk-derma- 

 toma III. These Proc. IV, p. .509. Verslagen der Kon. Akademie v. Welenscliappen, 

 22 Febr. 1902. 



