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Show 344 GEOGRAPIIICAL DISTRIBUTION. [CnAP. XII. pose that such wandering species have bee11; modified through natural selection in their new homes 1n relation to their new position, and we can understand the presence of endemic bats on islands, with the absence of all terres-trial mammals. Besides the absence of terrestrial mmnmals in relation 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 neighouring mainland~ and the presence in both of the same mamrniferous species or of allied S:Qecies in a more or less modified condition. Mr. Windsor Earl has made son1e 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 sidP the islands are situated on moderately steep submarine banks, and they are inhabited by closely allied or identical quadrupeds. No doubt some few anomalies occur in this great archipelago, and there is much difficulty in forming a judgment in some cases owing to the probable naturalisation of certain ma1n1nals 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 follow up this subject in all other quarters of the world; but as far as I have gone, the relation generally holds good. We see Britain separated by a shallow channel from Europe, and the mammals are the san1e on both sides ; we meet · with analogous facts on many islands separated by similar channels from Australia. The West Indian Islands 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 distinct. As the amount of modification in all cases depends to a certain degree on the lapse of time, and as during changes of level it is obvious that islands separated by shallow channels are more likely to have been continuously united within a recent period to the mainland than islands separated by deeper channels, we can understand the frequent OHAP. XII.] OCEANIC ISLANDS. l t . b 345 re a Ion etween the de th f h affinity of the mammat 0 • t e . sea and the degree of t~ose of a neighbourinO' cant. Inhabitants. of islands with t th 1on on e v1. ew of indoe peonnd I nent ' -an In exp 11. ca b le rela- . All the foregoing remarkse: acts. of cr~ation. Ishtnds:----:namely, the scarcity oJ\e.I~habitants ?f oceanic endemic forms in particular cl· · nn s,-~he richness in -the absence of whole r asses or sections of classes terrestrial mammals notwgJ'tolupt s, da~ of batrachians, and 0£ b t th . 1s an 1n o- the a s,- e singular proportions f 5 • presence of aerial -herbaceous forms having b 0 certain orders of plants &c.,-seem to me to accord b ~:n d~veloped into trees' sional means of transport h .e er With the view of occa~ the long course of time th aving: teen largely efficient in oceanic islands havino- bee a~~ Wit the view of all our tinuous land wHh theonear~t or~~rly connected by conview the migration would pr ~0~1In~nt; for on this latter plete; and if modification b~ aad Y. t laJe been lnore comlife wo';Ild have been nlore e u::ft te ' ~1~ th~ forms of ance With the pararnount · qt Y modified, In accordganism to organism. Imp or ance of the relation of or- I do not deny that ther in understandino- how se~ are nlany and grave difficulties 11?-ore remote isla~ds, wheth~:lst?l1 tlle .ii~liabitants of the cific form or modified s. :h ~etaining the same apereached their present h mce Blr arrival, could have many islands havino- ex1~:~· h ui . the probability of n~t a wreck now reikains ast . a ting-places, of which will here give a sin()'le ins ' mus not be overlooked. I culty. Almost all boc . ta?lce of one of the cases of diffi-d ean1c 1s ands e th . an s~allest, are inhabited b 1 ' d ven e most Isolated endemic species, but somethne[ b an -s~lells, generally by Dr. Aug. A. Gould has . y speCI.es found elsewhere. regar~ !o th~ land-shelfsiv:f t~everal Interesting cases in Now It IS notorious tha e Islands of the Pacific. by salt; their eg s at { land-shells are very easily killed s~a-water and ar! killed ~st. tsuc~ as I have tried, sink in VIew, some unknown b y ~ . et there must be on m transportal. Would' th ut. hlg~ly efficient means for thefr crawl on and adhere to ~J~~- tt~heb~ young o.ccasionally 15* ee o Irds roosting on the |