OF ISLAND FAUNAS 151 
Generally the fauna of islands like the Galapagos, called. 
oceanic by Wallace, is such that its members may 
be supposed to have been, at least to a large extent, 
accidentally introduced—by storms carrying winged 
animals out of their usual course, or by mechanical 
transportation on floating wood, &c. Incidentally we 
may note that the absence of mammals on oceanic 
islands has often important human consequences, for 
the paucity of sources of animal food tends to make 
their human inhabitants cannibals. 
As contrasted with oceanic islands we have the 
islands which are obviously merely separated portions 
of the adjacent continent upon whose continental shelf 
they stand. A good example is furnished by the British 
Isles, whose fauna is very similar to that of the adjacent 
continent, but shows impoverishment in several re- 
spects, apparently as a result of the glacial period. 
As Ireland was apparently cut off from the continent 
before Great Britain, and at a stage when many of the 
animals driven south by the ice had not had time to 
recover lost ground, we find that its fauna is poorer 
even than that of the larger island. The following 
figures, quoted from Wallace, will help to render the 
above statements more precise. Scandinavia possesses 
about 60 species of mammals, Great Britain 40, and 
Ireland 22; Belgium has 22 species of reptiles and 
amphibia, Great Britain 13, and Ireland only 4. The 
question as to the number of peculiar forms in the 
British fauna has been actively debated. That the 
red grouse (Lagopus scoticus) of the northern regions is 
peculiar is generally admitted, though it is nearly allied 
to the willow grouse of Scandinavia. We have also 
some peculiar fresh-water fish, most of which occur in 
lakes. The differences are, however, not very striking, 
