GENERAL LAWS OF DISTRIBUTION. 365 



the animals of temperate Asia differ more from those of 

 Europe than they do from those of America. 



-. Under the torrid zone the animal kingdom, as well 

 as the vegetable, attains its highest development. The animals 

 of the tropics are not only different from those of the tempe- 

 rate zone, but, moreover, they present the greatest variety 

 among themselves. The most gracefully proportioned forms 

 are found by the side of the most grotesque, decked with 

 every combination of brilliant colouring. At the same time, 

 the contrast between the animals of different continents is 

 more marked ; and, in many respects, the animals of the 

 different tropical faunas differ not less from each other 

 than from those of the temperate or frozen zones ; thus, 

 the fauna of Brazil varies as much from that of central Africa 

 as from that of the United States. 



I. This diversity upon different continents cannot de- 

 pend simply on any influence of the climate of the tropics ; 

 if it were so, uniformity ought to be restored in proportion as 

 we recede from the tropics towards the antarctic temperate 

 regions. But, instead of this, the differences continue to in- 

 se ; so much so, that no faunas are more in contrast than 

 those of Cape Horn, the Cape of Good Hope, and New Hol- 

 land. Hence other influences must be in operation besides 

 those of climate ; influences of a higher order, which are in- 

 volved in a general plan, and intimately associated with the 

 development of life on the surface of the earth. 



i . Faunas are more or less distinctly limited, according 

 to the natural features of the earth's surface. Sometimes two 

 faunas are separated by all extensive chain of mountains, like 

 the Rocky Mountains. Again, a desert may intervene, like 

 the desert of Sahara, which separates the fauna of Central 

 Africa from that of the Atlas and the Moorish coast, the latter 

 of which is merely an appendage to the fauna of Europe. 

 But the sea effects the most complete separation. The depths 

 of the ocean are quite as impassable for marine species as high 

 mountains are for terrestrial animals. It would be quite as 

 difficult for a fish or a mollusk to cross from the coast of 

 <;)e to the coast of America, as it would be for a reindeer 

 to pass from the arctic to the antarctic regions, across the 

 torrid zone. Experiments of dredging in very deep water 

 have also taught u> that the abyss of the ocean is nearly a 

 Not only are no materials found there for sustenance, 



