cHAr. XIX.] THE MADAGASCAR GROUP. 



419 



mammals — lemurs, insectivora, and small carnivora, together 

 with its ancestral struthious birds, and its reptiles and insects 

 of American or Australian affinity ; and at this period it was 

 joined to Madagascar. Before the later continental period of 

 Africa, 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- 

 forth was enabled to develop its singular forms of low-type mam- 

 malia, its gigantic ostrich-like ^pyornis, 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 birds 

 and insects which had reached them. 



The method we have followed in these investigations is to 

 accept the results of geological and palaeontological 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 

 organic relations of this island is due, partly to its having 

 derived its animal 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 else- 

 where ; others have spread far and wide over the globe, and 

 have survived only in a few remote countries — and especially in 



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