Geographical Distribution. 233 



is due to high antiquity is further indicated, accord- 

 ing to our theory, by the large number of species which 

 some of the types comprise. Thus, the 54 species of 

 Cossonidx may be referred to three types ; the 1 1 

 species of Bembidium form a group by themselves ; 

 and the Heteromera form two groups. " Now, each 

 of these types may well be descended from a single 

 species, which originally reached the island from 

 some other land ; and the great variety of generic 

 and specific forms into which some of them have 

 diverged is an indication, and to some extent a 

 measure, of the remoteness of their origin 1 ." But, 

 on the counter-supposition that all these 128 pecu- 

 liar species were separately created to occupy this 

 particular island, it is surely unaccountable that they 

 should thus present such an arborescence of natural 

 affinities amongst themselves. 



Passing over the rest of the insect fauna, which has 

 not yet been sufficiently worked out, we next find that 

 there are only 20 species of indigenous land-shells 

 which is not surprising when we remember by what 

 enormous reaches of ocean the island is surrounded. 

 Of these 20 species no less than 13 have become 

 extinct, three are allied to European species, while 

 the rest are so highly peculiar as to have no 

 near allies in any other part of the globe. So that 

 the land-shells tell exactly the same story as the 

 insects. 



Lastly, the plants likewise tell the same story. 

 The truly indigenous flowering plants are about 50 

 in number, besides 26 ferns. Forty of the former 

 and ten of the latter are peculiar to the island, 



1 Wallace, Island Life, p. 287. 



