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Show 394 GEOGRAPHICAL DISTRIBUTION. CHAP. XII. have formerly transported foxes, as s~ frequently no~v happens in the arctic regions. Yet It cannot be said that small islands will not support small mammals, for they occur in many parts of . the world on very small islands, if close to a continent; and hardly an island can be named on which our smaller quadrupeds have not become naturalised and greatly multiplied. It cannot be said, on the ordinary view of creation, that there has not been time for the creation of mammals; many volcanic islands are sufficiently ancient, as shown by the stupendous degradation which they have suffered and by their tertiary strata : there has also been time for the production of endemic species belonging to other classes; and on continents it is thought that mammals appear and disappear at a quicker rate than other and lower animals. Though terrestrial mammals do not occur on oceanic islands, aerial mammals do occur on almost every island. New Zealand possesses two bats found nowhere else in the world : Norfolk Island, the Viti Archipelago, the Bonin Islands, the Caroline and Marianne Archipelagoes, and l\1auritius, all possess their peculiar bats. Why, it may be asked, has the supposed creative force produced bats and no other mammals on remote islands? On my view this question can easily be answered ; for .no terrestrial mammal can be transported across a wide space of sea, but bats can fly across. Bats ~ave 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 studi~d this family, that many of the sam~ species have enormous ranges, and are found on continents and on far distant islands. Hence we have only t9 suppose that such wandering species have been modi- CHAP. XII. OCEANIC ISLANDS. 395 fied through· natural selection in their new homes · I t . h . lll rea Ion tot mr new position, and we can understand the presence of endemic bats on islands, with the absence of all terrestrial mammals . . Besides the absence of terrestrial mammals in relation to the remoteness of islands from continents ther is. also a relation, to a certain extent independent 0~ ~1stance, between t~e dept.h of the sea separating an Island .from the ne1ghbounng mainland, and the prese~ ce In b?th. of the same mammiferous species or of all~ed spemes In a more or less modified condition. Mr. Windsor Earl has made some striking observations on thi~ he~d in regard to the great Malay Archipelago, which IS trave1~sed near Celebes by a space of deep ocean ; ~nd this space separates two widely distinct ~ammahan faunas. On either side the islands are Situa.ted o~ moderately deep submarine banks, and they are Inhabited by closely allied or identical quadrupeds. No doubt some few anomalies occur in this great archipelag~, and there is m~ch difficulty in forming a judgment In some cases owing to the probable naturalisati.on of certain mammals through man's agency; but we s~all 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 same 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 |