1 88 EVOLUTION OF TO-DAY. 



rence of the same species of fresh-water hydra in the 

 'rivers of the two hemispheres. The wide distribu- 

 tion of land animals is sometimes equally surprising. 

 Two species of the genus tapir occur in South 

 America, and another in the Moluccas. The tro- 

 gon, a gorgeously colored, insect-eating bird, is 

 abundant in Asia and Africa, and a single genus is 

 found in South America. Two species of anthro- 

 poid apes are found in West and Central Africa, and 

 two others in Sumatra. All such cases as. these, 

 though not insuperable difficulties, are rather puz- 

 zling. The distribution of the edentates offers per- 

 haps the hardest problem of all. These animals 

 appeared in South America, Africa, and Asia long 

 before they did in North America. And since we 

 can see no means by which South America could 

 have received its inhabitants except through North 

 America, it is very surprising to find edentates in 

 the former country earlier than in the latter. To 

 solve this puzzle, some naturalists have not hesitated 

 to assume a hypothetical continent which formerly 

 united Africa and South America ; while others, 

 among whom are Huxley and Wallace, suppose that 

 there once existed a tract of land in the northern 

 Pacific which was the birthplace of the edentates, 

 and which being connected at times with South 

 America and Asia, furnished them with their supply 

 of this order. Negative evidence in paleontology is, 

 however, of little value, and it may yet be found that 

 North America had its edentates earlier than the 

 southern continent ; but at present we do not know 

 what to do with this case. Something of a surprise, 



