206 GREAT BRITAIN AND MADAGASCAR. [CH. IV 



impassable barrier to mammalian life; for the common 

 mouse, which, as has been said, occurs there, could easily 

 be, and doubtless has been, conveyed there by man's 

 agency. With the Amphibia the difficulties are even 

 greater; for in their case there is not only the diffi- 

 culty of transport, but the serious additional difficulty 

 that sea-water is fatal to them. It might be urged that 

 as some of these purely oceanic islands are of large 

 dimensions and have probably been larger, mammalian 

 life might have come into existence upon them independ- 

 ently. This assumption however would be entirely 

 contrary to our ideas of evolution; indeed it is not 

 necessary to argue from any a priori point of view, for we 

 are confronted with the fact that some oceanic islands at 

 any rate — e.g. S. Helena — are not incapable of supporting 

 mammalian life, for imported animals do well, and yet 

 they are totally without an indigenous fauna of the kind. 

 On the other hand, there is no doubt at all that both 

 Great Britain and Madagascar are severed portions of 

 continents, which were amply stocked with mammalian 

 life when they were finally cut adrift. 



Although there is this general similarity between the 

 two islands just mentioned, it is clear that there are also 

 differences, and considerable differences too. The mam- 

 malian fauna of Great Britain, and for the matter of that 

 the fauna in general, is poor in peculiar forms, restricted 

 to the archipelago and not found living in the continent 

 of Europe; there are a good many peculiar species, it 

 is true, but very few in comparison to the fauna as a 

 whole. 



