INTRODUCTION. 21 



of his particular observation bearing on this interest- 

 ing subject. 



On the other hand, Mr. Simpson, who has gained 

 considerable experience of oceanic dispersal in the 

 West Indian region, though he acknowledges having 

 often noticed bamboo rafts, which would be suitable in 

 the transportal of invertebrates, nevertheless does not 

 attach much importance to this means of distribution. 

 " The fact," he remarks, " that the operculates (oper- 

 culate land-shells) form so large a proportion of the 

 Antillean land-snail fauna, that a majority of the 

 genera are found on two or more of the islands and 

 the mainland, while nearly every species is absolutely 

 restricted to a single island, appears to me to be 

 very strong testimony in favour of a former general 

 land connection" (p. 428). 



Amphibians are affected in the same manner by 

 sea-water as slugs are. The accidental transportal of 

 an amphibian from the mainland to an island is there- 

 fore almost inconceivable. And the presence of frogs, 

 toads, and newts in the British Islands, in Corsica 

 and Sardinia, indicates, if nothing else did, that all 

 these islands were at no distant date united with the 

 continent of Europe. 



As regards the terrestrial reptiles, the case is some- 

 what different. Many of them readily take to the 

 sea, and, as probably all snakes and some Hzards are 

 able to swim, it is possible that sometimes, though 

 very rarely, they might reach islands if not too far 

 from a continent. Instances of accidental transportal 



