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are the same on both sides; and so it is with all the islands near the shores of Australia. The West Indian Islands, on the other hand, stand on a deeply submerged bank, nearly 1000 fathoms in depth, and here we find American forms, but the species and even the genera are quite distinct. As the amount of modification which animals of all kinds undergo, partly depends on the lapse of time, and as islands separated from each other or from the mainland by shallow channels are more likely to have been continuously united within a recent period than islands separated by deeper channels, we can understand how it is that a relation exists between the depth of the sea separating two mammalian faunas, and the degree of their affinity,— a relation which is quite inexplicable on the theory of independent acts of creation.
The foregoing statements in regard to the inhabitants of oceanic islands,— namely, the fewness of .. the species, with a large proportion consisting of endemic forms— the members of certain groups, and not of other groups in the same class, having been modified— the absence of certain whole orders, as of batrachians and of terrestrial mammals, notwithstanding the presence of aërial bats,— the singular proportions of certain orders of plants,— herbaceous forms having been developed into trees, &c.,— seem to me to accord better with the belief in the efficiency of occasional means of transport, carried on during a long course of time, than with the belief in the former connection of all .. oceanic islands ... with the nearest continent; for on this latter view it is probable that the various classes would have immigrated more uniformly, and from the species having entered in a body their mutual relations would not have been much disturbed, and consequently they would have been modified either not at all or in a more equal manner.