194 '^^E POPULAR SCIENCE MONTHLY. 



younger and more liigUy developed competitors solely in virtue 

 of tkeir singular combination of desert-resisting qualities. 



Now, it must at once strike everybody as a curious circum- 

 stance in the geography of animals that the existing cameloids 

 should be so strangely distributed — one group of them in the des- 

 ert region of Asia and Africa, the other group away across the 

 world among the snowy slopes of the Andes of South America. 

 What can be the meaning of so quaint a freak of distribution ? 

 Why should the two surviving cameloid tribes be thus separated 

 from one another by half the earth's surface, and by many deep 

 seas and shadowy mountains — one in the Old World and one in 

 the New ; one in the desert and one in the uplands ; one in the 

 northern hemisphere and one in the southern ? Clearly, the an- 

 swer suggested alike by geological facts and by analogies else- 

 where, is simply this : we have here, as it were, two little surviv- 

 ing biological islands, colonies of an ancient race which once cov- 

 ered both worlds alike with its numerous members. Time was 

 when the camels or their allies were of cosmopolitan distribution. 

 They ranged, no doubt, the Eocene plains of all the great conti- 

 nents. But they are an ancient and in many respects an undevel- 

 oped ungulate form, which has become extinct elsewhere in the 

 intermediate regions through the fierce competition of the higher 

 ruminants, and has lingered on only under special circumstances 

 in two remote corners of the world — in the deserts of Arabia and 

 in the Andes of Peru. 



The llamas and alpacas, as the lower and less specialized type 

 of the two, explain best the true systematic position of the family. 

 For South America, as everybody knows, is in many respects a very 

 antique biological province. Less ancient in its life-forms than 

 Australia, that world of living mesozoic fossils, it yet retains in 

 many places the scattered remnants of its extremely old-fashioned 

 fauna. There is reason to believe, indeed, that the circumpolar 

 continent — Europe, Asia, and North America — was once for many 

 ages continuous, while Australia, South Africa, and the South 

 American peninsula formed separate islands in a wide and wind- 

 ing southern sea. Hence the higher life-forms developed rapidly 

 in the broad and varied northern land -mass, while more anti- 

 quated types continued to live on, uninfluenced by their compe- 

 tition, in the three isolated southern provinces. Of these three, 

 Australia alone still remains a great island ; but South Africa has 

 been joined to the Mediterranean world by a gradual upheaval of 

 the Saharan area ; while the Isthmus of Panama, still later in 

 date, apparently, has formed a great natural bridge by which 

 some of the North American land-animals have been able to in- 

 vade the comparatively unpeopled tropical realms of the low 

 southern species. In both cases, however, many of the low local 



