^^2 THE DISPERSAL OF SHELLS. 



forbidding. Much of the rich upper soil, which could 

 only be retained on the steep slopes so long as it was 

 protected by vegetation, has been washed away by the 

 violent rains.^ As a result, w^e find that of the twenty- 

 seven truly indigenous species of terrestrial mollusca 

 belonging to the island — and the fact has already been 

 mentioned — only seven now survive, the remainder 

 having been exterminated, Mr. Edgar Smith remarks, 

 " by the destruction of the primeval forests.'^ Foreign 

 snails have been introduced, and are now living on the 

 island, imported probably, perhaps as ova, with " some of 

 the many introduced plants ;'^' the presence oiHyalinia 

 cellaria, for instance, has just been referred to: these, 

 however, from a naturalist's point of view at least, form 

 no real compensation for the loss of aboriginal forms, 

 the destruction of an inoffensive member of a native 

 fauna — more especially when highly peculiar — being an 

 irreparable calamity. 



Shells have been intentionally dispersed by man to a 

 considerable extent. Both land and fresh-w^ater kinds, as 

 everyone is aware, have frequently been " planted/' 

 chiefly by shell-collectors, in localities where they were 

 previously unknown, and permanent additions to faunas, 

 it will be admitted, have thus been made. To some 

 persons the transplantation of foreign or local snails 

 to spots near their residences seems to have special 

 fascination, and a whole volume might probably be filled 



' Wallace, " Island Life,'" 1880, pp. 281-4 ; ed. 2, 1892, pp. 292-5 ; 

 and see also Darwin's " Journal," ed. 2, 1845, PP- 488-9. 

 - See Darwin's ''Journal," pp. 489-90. 



