352 Absence of Terrestrial Mammals Chap. xiii. 



traversed near Celebes by a space of deep ocean, and this separates 

 two widely distinct mammalian faunas. On either side the islands 

 stand on a moderately shallow submarine bank, and these islands 

 are inhabited by the same or by closely allied quadrupeds. I have 

 not as yet had time to follow up this subject in all quarters of the 

 world; but as far as I have gone, the relation holds good. For 

 instance, Britain is separated by a shallow channel from Europe, 

 and the mammals 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 modi- 

 fication which animals of all kinds undergo, partly depends on the 

 lapse of time, and as the islands which are separated from each 

 other or from the mainland by shallow channels, are more likely 

 to have been continuously united within a recent period than the 

 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, but 

 not those of other groups in the same class, having been modified— 

 the absence of certain whole orders, as of batrachians and of ter- 

 restrial mammals, notwithstanding the presence of aerial 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 trans- 

 port, 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 either have 

 not been modified, or all the species in a more equable manner. 



I do not deny that there are many and serious difficulties in 

 understanding how many of the inhabitants of the more remote 

 islands, whether still retaining the same specific form or subse- 

 quently modified, have reached their present homes. But the- 

 probability of other islands having once existed as halting-places, 

 of which not a wreck now remains, must not be overlooked. I will 



