282 THE INFLUENCE OF INANIMATE SUKROUN DINGS. 



turn, a land mollusc living on the seashore, and having a very 

 peculiar mode of life and anatomical structure, is found absolutely 

 identical in the Red Sea, the Philippines, and North Australia, 

 and on the Chinese and Japanese coasts. Another species of the 

 same genus, Onchidium tonganum (see fig. 72), is found alike in 

 the Tonga Islands and the Mauritius. Different species of the 

 genera Auricula and Scarabus, belonging to the Pulmonata, of 

 which the larvae have an operculum and probably float in the 

 sea, have an equally wide distribution. All these, and many 

 other species which cannot be mentioned here, are easily trans- 

 ported by currents, either in the larva state or fully grown, and 

 the general similarity I have indicated of the marine fauna, 

 from the Red Sea as far as the western half of the Pacific, must 

 be the result of a diffusion of species effected by constant 

 marine currents. 



The influence of such currents is even more conspicuous in 

 the distribution of many land-animals, although at first sight it 

 might seem paradoxical to say that the distribution of animals 

 living on laud can be affected by currents in the sea. The evi- 

 dence, however, is easily produced. If we reflect, to begin with, 

 that all Land rnollusca, the great majority of Insects, and many 

 Reptiles and Birds, being vegetable-feeders, are directly depen- 

 dent for their existence on certain species of plants, it is evident 

 that their presence in particular spots, as well as their geogra- 

 phical distribution, depends in the most direct manner on the 

 action of currents, since these it is which principally determine 

 the distribution of the plants on which they feed. Granting 

 that a mouophagous insect were by any means transported to 

 an island where it did not find the only plant adapted for its 

 support and to which that plant never could be brought even by 

 currents, that species must inevitably perish. But there is yet 

 another way in which currents may affect the distribution of 

 animals, besides this indirect mode by means of the plants they 

 feed on. Many Insects are easily transported as larvae, in and on 

 floated trees and wood ; small Mammals, no doubt, are also car- 

 ried in this way from one place to another ; the tame is the case 

 with many Reptiles and Amphibia, and it is more than probable 

 that land-snails can trav 1 only in this way, and in no other, 



