254 DISTRIBUTION OF ANIMALS. SECT. XXVI. 



served have led to the conclusion that vegetable creation must 

 have taken place in a number of distinctly different centres, as 

 the islands and continents rose above the ocean, each of which 

 was the original seat of a certain number of peculiar species 

 which at first grew there and nowhere else. Heaths are exclu- 

 sively confined to the Old World ; and no indigenous rose-tree 

 has ever been seen in the New, the whole southern hemisphere 

 being destitute of that beautiful and fragrant plant. But this is 

 still more confirmed by multitudes of particular plants, having 

 an entirely local and insulated existence, growing spontaneously 

 in some particular spot, and in no other place : for example, the 

 cedar of Lebanon, which grows indigenously on that mountain, 

 and in no other part of the world. On the other hand, as there 

 can be no doubt that many races of plants have been extin- 

 guished, Sir John Herschel thinks it possible that these solitary 

 instances may be the last surviving remnants of the same group 

 universally disseminated, but in course of extinction, or that 

 perhaps two processes may be going on at the same time : 

 " Some groups may be spreading from their foci, others retreat- 

 ing to their last holds." 



The same laws obtain in the distribution of the animal crea- 

 tion. Even the microscopic existences, which seem to be the 

 most widely spread, have their specific localities; and the 

 zoophyte (N. 219), occupying the next lowest place in animated 

 nature, is widely scattered through the seas of the torrid zone, 

 each species being confined to the district and depth best suited 

 to its wants. Mollusks, or the animals of shells, decrease in 

 size and beauty with their distance from the equator ; and not 

 only each sea and every basin of the ocean, but each depth, is 

 inhabited by its peculiar tribe of fish. Indeed, MM. Peron and 

 Le Sueur assert that, among the many thousands of marine 

 animals which they had examined, there is not a single animal 

 of the southern regions which is not distinguishable by essential 

 characters from the analogous species in the north em seas. 



Reptiles are not exempt from the general law. The saurian 

 (N. 220) tribes of the four quarters of the globe differ in 

 species ; and, although warm countries abound in venomous 

 snakes, they are specifically different in different localities, and 

 decrease both in numbers and in the virulence of their poison 



