1/4 THE DISPERSAL OF SHELLS. 



suppose, are usually placed either in the hollows 

 or under the bark of trees. In such situations, 

 protected, or partially protected, for a time from con- 

 tact with sea water, ova might possibly be carried 

 with floating trees over small arms of the sea, 

 and perhaps even to islands, though rarely if ever to 

 very remote ones. The animals themselves thus hiding 

 might also be carried, I think, in a similar way. It 

 is just possible, also, that eggs may be occasionally 

 carried over the sea, at least for short distances^ in the 

 cavities of pumice, or in earth at the roots of trees. 

 Large numbers, both adults and ova, must certainly be 

 carried out to sea by large tropical rivers with floating 

 rafts or islands, which have already been referred to, and 

 if such objects have ever been stranded upon more or 

 less distant shores so as to permit their inhabitants to 

 be " poured out as from an ark," which was regarded as 

 possible by Lyell,' any number of slugs may have 

 been thus transported. Hurricanes and whirlwinds 

 may have carried the creatures and their eggs (some- 

 times laid amongst dead leaves) over straits and small 

 arms of the sea, and the just-hatched young are as 

 likely as those of snails to crawl upon the feet of 

 ground-roosting birds, and thus possibly they may be 

 carried over sea, provided, of course, that they adhered 

 firmly ; this may be the case at a very early age, but 

 later, I find, and more especially when young than 

 adult, the creatures often let themselves drop purposely, 



' See "Principles," ii. p. 366. 



