138 STUDIES IN THE EVOLUTION OF ANIMALS 



Then in the Natural History Museum we find that Propithecus 

 coquereli has the front of all four legs brown, and the posterior of the 

 legs and back of the body wholly white ; that P. coronatus is brown 

 on the abdomen and white on the back ; that P. Edwardsii is dark 

 brown everywhere except \the posterior half of the back, which is 

 white ; that Varesia varia is black on the abdomen and front of 

 legs, and yellow-brown on the back. 



(Further, the Egyptian ^orille or the parti-coloured Weasel has a 

 white back, striped longitudinally with intense black, and its ventral 

 surfaces and legs are black. 



These might be sufficient to prove that light cannot be the 

 cause of this difference in the colorations of the upper and lower 

 surfaces of mammals. But if, in addition, we take that large class 

 of mammals, which have a dark back and a lighter-coloured abdo- 

 men, we shall find that, in many cases, such as in the Gazelles, the 

 Black Buck of India, the black-backed Jackal of S. Africa, etc., 

 there is a distinct and very sharp line of demarcation, along the 

 flanks, between the two colours. This sharp line of demarcation 

 alone would be wholly opposed to the theory under review, for 

 there is no known property of light by which such a result could 

 be produced on the flanks of these animals. Moreover, the front 

 aspect of the legs of these animals is in most cases darker than the 

 hind aspect ; and we cannot suppose that the sun rays always beat 

 upon the legs from the front. It is obvious that in walking away from 

 the sun the hind aspect would be more lighted ! The same objec- 

 tion can be brought against this view, in the case of those Antelopes 

 which have patches of white either in front or behind, and which 

 Dr. Wallace would call * recognition marks.' Then what shall we 

 say of all those Antelopes and Deer which, on a dark ground, are 

 either spotted or striped with white ? Why have these white marks 

 not been obliterated by the light? 



