352 GEOGRAPHICAL DISTRIBUTION. 



eastern islands of the Pacific with another and totally dis- 

 tinct fauna. So that three marine faunas range northward 

 and southward in parallel lines not far from each other, 

 under corresponding climate ; but from being separated 

 from each other by impassable barriers, either of land or 

 open sea, they are almost wholly distinct. On the other 

 hand, proceeding still farther westward from the eastern 

 islands of the tropical parts of the Pacific, we encounter 

 no impassable barriers, and we have innumerable islands as 

 halting-places, or continuous coasts, until, after travelling 

 over a hemisphere, we come to the shores of Africa ; and 

 over this vast space we meet with no well-defined and dis- 

 tinct marine faunas. Although so few marine animals are 

 common to the above-named three approximate faunas of 

 Eastern and Western America and the eastern Pacific 

 islands, yet many fishes 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 affinity of the productions of the same con- 

 tinent 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, though nearly related, replace each other. He 

 hears from closely allied yet distinct kinds of birds, notes 

 nearly similar, and sees their nests similarly constructed, 

 but not quite alike, with eggs colored in nearly the same 

 manner. The plains near the Straits of Magellan are in- 

 habited 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 

 inhabiting Africa and Australia under 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 bizcacha ; we look to the waters, and we 

 do not find the beaver or rauskrat, but the coypu and capy- 

 bara ; rodents of the South American type. Innumerably 



