176 THE DISPERSAL OF SHELLS. 



lone islet, at no great distance, all the moist surfaces of 

 which, previously uninhabited by slugs perhaps, might 

 possibly be found, after a few centuries, as some traveller 

 might record, swarming with a kind common to the 

 mainland. We are bound to conclude, however, I think, 

 that in all probability dispersal over sea, with subse- 

 quent colonization, even to short distances, is very rare, 

 and such dispersal over wide stretches, though perhaps 

 not impossible, can hardly be supposed to have 

 happened, by any known means, more than once or 

 twice in the course of vast ages. One other point 

 deserves attention. Slugs are known to be largely 

 eaten by many birds ; we find, for instance, that young 

 chickens and ducks are sometimes cmplo}'ed with good 

 results for the purpose of keeping the creatures within 

 bounds in kitchen gardens ; when the former are allowed 

 the free range of a garden they may be seen, it is 

 said, at daybreak, regularly searching rows of cabbages 

 and broccoli, picking up slugs, etc. ; plovers and gulls 

 also, thus employed, are stated to be very useful, 

 and a tame petrel is said to have proved valuable for 

 the same purpose.^ If the creatures can survive in 

 the crop for a icw hours, it would certainly seem that 

 they may be transported, as already suggested for 

 snails, for short distances, and if they can survive say 

 for twelve or eighteen hours, they may be carried over 

 sea, in exceptional circumstances, according to an 



' " Garden," x. (1S76), p. 435 ; xiii. (1878), pp. 275, 304, 350 ; xvi. 

 (1879), p. 391 ; " Gardeners' Chronicle," 1878, p. 664 ; "Science 

 Gossip," 1 868. p. 46; etc. 



