EVOLVING THE CAMEL. 201 



But water is even scantier in the desert than food ; and against 

 want of water, therefore, the camel has had to provide himself, 

 functionally at least, if not structurally, quite as much as against 

 want of herbage. His stomach has accordingly acquired the power 

 of acting as an internal reservoir, and he can take in as much 

 water at the Bahrs or Wadys, where he rests for a while on his 

 toilsome march, as will supply his needs for four or five days 

 together. There are some differences in this respect, however, 

 between the two chief varieties of the camel. The African kind 

 is most abstemious, and best adapted to sandy deserts ; the Bac- 

 trian, a product of more varied and better-watered country, is 

 larger and stronger, but less patient of hunger and thirst, while 

 at the same time it can manage to subsist and to make its way 

 into somewhat rockier and more rugged country. 



One other adaptive peculiarity the camel possesses which marks 

 it out essentially as a desert-born animal, modified for generations 

 by the baking expanse of Sahara or the Arabian sand- wastes. On 

 those scorching surfaces a horse could not lie down to rest in the 

 eye of the sun without scalding or excoriating his tender skin. 

 But all the parts of the camel's body which touch the sweltering 

 sand in his ordinary patient kneeling position are provided with 

 callosities of thickened hide, which enable him to rest on the 

 burning surface without danger or discomfort. The only other 

 desert-haunting ruminant of similar habits, the giraffe, has analo- 

 gous callosities for the same purpose on his breast and knees. 

 Such adaptive characters, however, are never a key to real rela- 

 tionship ; they necessarily result from mere exposure to the same 

 circumstances ; and hence we get the seemingly paradoxical prin- 

 ciple, so well enunciated by Mr. A. R. Wallace, that the more use- 

 ful any organ or point of structure is to its possessor, the less is 

 its value as a test of systematic position. Unseen little bones and 

 internal organs, which fail to strike the imagination of the outside 

 observer, are rightly used as the keys to underlying relationship 

 by the systematic biologist. The real affinities of the camel are 

 closest, indeed, not with the giraffe which so strongly resembles 

 it, but with the llama and alpaca, so remotely connected in outer 

 seeming, and so widely separated from it in space by an entire 

 hemisphere. 



Camels, llamas, and alpacas alike, then — to sum up the conclu- 

 sion to which we have all along been tending — represent a very 

 simple and early ruminant type, unmarked by any of those higher 

 features induced in the ruminants of the open plains of the great 

 continents by the necessity for protection from the advanced car- 

 nivores. They recall for us in their main points of structure, as 

 well as in their low and undeveloped grade of intelligence, the 

 general characteristics of the ruminant race at the dawn of its 



