Geographical Distribution. 225 
‘pean forms. Lastly, there are 480 known species of 
plants, of which 40 are peculiar, though allied to 
European speties. 
Bermudas.—A small volcanic group of islands, 700 
miles from North Carolina. Although there are 
about 100 islands in the group, their total area does 
not exceed 50 square miles. The group is surrounded 
by water varying in depth from 2,500 to 3,800 fathoms. 
The only terrestrial Vertebrate (unless the rats and 
mice are indigenous) is a lizard allicd toan American 
form, but specifically distinct from it, and therefore a 
solitary species which does not occur anywhere else in 
the world. None of the birds or bats are peculiar, 
any more than in the case of the Azores; but, as in 
that case, a large percentage of the land-shells are so 
—namely, at least one quarter of the whole. Neither 
the botany nor the entomology of this group has been 
worked out ; but I have said enough to show how re- 
markably parallel are the cases of these two volcanic 
groups of islands situated in different hemispheres, but 
at about the same distance from large continents. In 
both there is an extraordinary paucity of terrestrial 
vertebrata, and of any peculiar species of bird or beast. 
On the other hand, there is in both a marvellous 
wealth of peculiar species of insects and land-shells. 
Now these correlations are all abundantly intelligible. 
It is a difficult matter for any terrestrial animal to 
cross 90o, or even 700, miles of ocean. therefore only 
one lizard has succeeded in doing so in one of the two 
parallel cases; and. living cut off from intercrossing 
with its parent form, the descendants of that lizard 
have become modified so as to constitute a peculiar 
species. But it is more easy for large flying animals 
. Q 
