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Show 41B ISLAND LIFE. [PAil.'!' 11. helps to supply us w·i th· a practw· al demonstrat 'w n °f them· W. e find that the enti·r e group contam· s J·U S t that amoun. t of Ind1an forms which could well have passed from island ~0 Isl~nd.; t~at many of these forms are slightly modified s~ecies,. Indwati~g that the migration occurred during late Tertiary .times, wh1le others are distinct genera, indicating a more a~Cient con.ncction; but in no one case do we find animals whwh. necessitate an actual land-connection, while the numerous Indian types of mammalia, reptiles, birds, and insects, which must certa~nly have passed over had there been such an actualland-connectwn, are t~tally wanting. The one fact which has been supposed to require such a connection-the distribution of th~ le~urscan be far more naturally explained by a general chsperswn of the group from Europe, where we k~ow it existed in Eoce.nc times; and such an explanation applies equally to the affimty of the Insectivora of Madagascar and Cuba; the snakes (Herpctodryas, &c.) of Madagascar and America; and the lizards (Cryptoblepharus) of Mauritius and Australia. To suppose, in all these cases, and in many others, a direct land-connection, is really absurd, because we have the evidence afforded by geology of wide differences of distribution directly we pass beyond the most recent deposits; and when we go back to Mesozoic-and :::;till more to Palreozoic-times, the majority of the groups of animals and plants appear to have had a world-wide range. A large number of our European Miocene genera of vertebrates were also Indian or African, or even American; the South American Tertiary fauna contained many European types ; w bile many Mesozoic reptiles and mollusca ranged from Europe and North America to Australia and New Zealand. By direct proof (the occurrence of wide areas of marine deposits .of Eocene age), geologists have established the fact that Africa was cut off from Europe and Asia by an arm of the sea in early Tertiary times, forming a large island-continent. By the evidence of abundant organic remains we know that all the types of large mammalia now found in Africa (but which are absent from Madagascar) inhabited Europe and Asia, and many of them also North America, in the Miocene period. At a still earlier epoch Africa may have received its lower types of CHAP. XIX.] THE MADAGASCAR GROUP. 419 m.anu?als-lemurs, insectivora, and smaJl carnivora, together With Its ancestral struthious birds, and its reptiles and insects ?f. American or Australian affinity ; and at this period it was JOm.ed to Madagascar. Before the later continental period of Afnca, Madagascar had become an island; and thus, when the large mammalia from the northern continent overran Africa they were prevented from reaching Madagascar, which thence~ fort~ w.as e~able~ to develop its singular forms of low-type mammaha, 1ts gigantiC ostrich-like ..:Epyornis, its isolated birds, its remarkable insects, and its rich and peculiar flora. From it the adjacent islands received such organisms as could cross the sea· while they transmitted to Madagascar some of the Indian bird~ and insects which bad reached them. The method we have followed in these investigations is to accept the results of geological and palreontological science, and the ascertained facts as to the powers of dispersal of the various animal groups; to take full account of the laws of evolution as affecting distribution, and of the various ocean depths as implying recent or remote union of islands with their adjacent continents ; and the result is, that wherever we possess a sufficient knowledge of these various classes of evidence~ we find it possible to give a connected and intelligible . explanatiOn of all the most striking peculiarities of the organic world. In Madagascar we have undoubtedly one of the most difficult of these problems; but we have, I think, fairly met and conquered most of its difficulties. The complexity of the org~nic ~elati~ns of this island is due, partly to its having flenved 1ts ammal forms from two distinct sources-from one continent through a direct land-connection, and from another by means of intervening islands now submerged; but, mainly to the fact of its having been separated from a continent which is now, zoologically, in a very different condition from what it was at the time of the separation; and to its having been thus able to preserve a number of types which may date back to the Eocene, or even to the Cretaceous, period. Some of these types have become altogether extinct elsewhere; others have spread far and wide over the globe, and have survived only in a few remote countries-and especially in E E 2 |
