Chap. XII. 
OCEANIC ISLANDS. 
395 
terrestrial mammal can be transported across a wide 
space of sea, but bats can fly across. Bats have been 
* seen wandering by day far over the Atlantic Ocean; 
and two North American species either regularly or 
occasionally visit Bermuda, at the distance of 600 miles 
from the mainland. I hear from Mr. Tomes, who has 
specially studied this family, that many of the same 
species have enormous ranges, and are found on conti¬ 
nents and on far distant islands. Hence we have only 
to suppose that such wandering species have been modi¬ 
fied through natural selection in their new homes in 
relation to their new position, and we can understand 
the presence of endemic bats on islands, with the ab¬ 
sence of all terrestrial mammals. 
Besides the absence of terrestrial mammals in rela¬ 
tion to the remoteness of islands from continents, there 
is also a relation, to a certain extent independent of 
distance, between the depth of the sea separating an 
island from the neighbouring mainland, and the pre¬ 
sence in both of the same mammiferous species or of 
allied species in a more or less modified condition. Mr. 
Windsor Earl has made some striking observations on 
this head in regard to the great Malay Archipelago, 
which is traversed near Celebes by a space of deep 
ocean; and this space separates two widely distinct 
mammalian faunas. On either side the islands are 
situated on moderately deep submarine banks, and they 
are inhabited by closely allied or identical quadrupeds. 
No doubt some few anomalies occur in this great archi¬ 
pelago, and there is much difficulty in forming a judg¬ 
ment in some cases owing to the probable naturalisation 
of certain mammals through man’s agency; but we 
shall soon have much light thrown on the natural 
history of this archipelago by the admirable zeal and 
researches of Mr. Wallace. I have not as yet had time to 
