METHODS - 



PAL^ONTOLOGICAL 



45 



form than their skeletons would lead one to expect, as do also 

 the Lion, the Tiger and the Leopard. The curious and ex- 

 ceptional colour-pattern of the Okapi, that remarkable giraffe - 

 like animal but lately discovered in the equatorial forests of 

 western Africa, could never have been inferred from a study 

 of the skeleton alone. However, even in the problem of colour- 

 patterns there is more to go upon than sheer guess-work, for 

 certain definite principles of animal colouration have been 

 ascertained ; the great difficulty lies in the application of these 

 principles to a particular case. It is quite certain that the 

 naked, hairless skin is never primitive, but always a compara- 

 tively late acquisition and, in many mammalian orders, is 

 not found at all. Aside from a few domesticated animals, 

 this type of skin occurs only in very large herbivorous mammals 

 living in warm climates, such as elephants, rhinoceroses and 

 hippopotamuses, in a few burrowers, and in marine mammals, 

 like the walruses, whales, porpoises, etc. Useful hints as to the 

 colouring of ancient and extinct forms may be gathered from 



Fig. 4. — Wild sow and pigs, showing the uniform colour of the adult and stripes of 



the young. 



