324 GKOGKAPIIICAL DISTRIBUTION. Chap. XI. 



distinct fauna. So that three marine faunas range far north- 

 ward and southward in parallel lines not far from each other, 

 imder corrcspondini^ climates ; but from beinf^ separated from 

 each other by impassable barriers, either of land or open sea, 

 they are almost wholly distinct. On the other hand, proceed- 

 ing still farther westward from the eastern islands of the tropi- 

 cal parts of the Pacific, we encounter no impassable barriers, 

 and we have innumerable islands as halting--places, or continu- 

 ous coasts, imtil after travelling over a hemisphere we come to 

 the shores of Africa ; and over this vast space we meet witli 

 no well-defined and distinct marine faunas. Although so few 

 shells, crabs, or fishes, arc common to the above-named three 

 approximate faunas of Eastern and Western America and the 

 eastern Pacific islands, yet many fish range from the Pacific 

 into the Indian Ocean, and many shells are common to the 

 eastern islands of the Pacific and the eastern shores of Africa, 

 on almost exactly opposite meridians of longitude. 



A third great fact, partly included in the foregoing state- 

 ment, is the ailinity of the productions of the same continent, 

 or of the same sea, though the species themselves are distinct 

 at different points and stations. It is a law of the widest 

 generality, and every continent offers innumerable instances. 

 Nevertheless the naturalist, in travelling, for instance, from 

 north to south, never fails to be struck by the manner in which 

 successive groups of beings, specifically distinct, nearly related, 

 replace each other. He hears from closely-allied, yet distinct 

 kinds of birds, notes nearly similar, and sees their nests simi- 

 larly constructed, but not quite alike, with eggs colored in 

 nearly the same manner. The plains near the Straits of Magel- 

 lan are inhabited by one species of Rhea (American ostrich), 

 and northward the plains of La Plata by another species of the 

 same genus ; and not by a true ostrich or emu, like those in- 

 habiting Africa and Australia imdcr the same latitude. On 

 these same plains of La Plata, we see the agouti and bizcacha, 

 animals having nearly the same habits as our hares and rabbits 

 and belonging to the same order of Rodents, but they plainly 

 display an American type of structure. We ascend the lofty 

 peaks of the Cordillera, and we find an alpine species of biz- 

 cacha ; we look to the waters, and we do not find the beaver 

 or nuisk-rat, but the coypu and capybara, rodents of the South 

 Americaii ty\)C. Inmunerable other instances could be given. 

 If we look to the islands off the American shore, however much 

 they may differ in geological structure, the inhabitants are 



