ORIGIN OF ISLANDS. 229 



extremely numerous, can be brought into closer union 

 and reduced to the smallest number possible, as by our 

 theory the Mammalia have but one point of derivation, 

 and if we can herewith harmonize the geological succes- 

 sion of the organisms examined, or, in other words, har- 

 monize the horizontal distribution with the vertical or 

 historical sequence, animal geography will then approach 

 the solution of its task. Wallace and Riitimeyer's works 

 are therefore an important advance, as the former has 

 given detailed evidence that the fauna of the complex 

 and extensive Australio-Indian Archipelago is by no 

 means self-dependent, but consists merely of offshoots 

 of the continents ; and the latter, in a grand survey of 

 the entire surface of the earth, has reduced the centres 

 of distribution to the simplest proportions as yet 

 possible. 



The comparison of insular and continental faunas is 

 naturally of great interest. For should it appear that, 

 with respect to the animal world, islands are one and all 

 mere appendages of the continents, the problem would 

 at once be vastly simplified. If we follow Peschel's 

 luminous exposition of the origin of islands,'^ we have 

 first to deal with the fragments of continents. A great 

 number of islands, such as Great Britain and the great 

 Asiatic islands, may be recognized at once as fragments 

 of still existing continents. On the other hand, Mada- 

 gascar and the Seychelles are not, as might be con- 

 jectured, a segment of Africa, but the remnant of a 

 former continent very peculiar in its flora and fauna. 

 Other islands originate either from submarine volcanoes 

 or from corals, and in the latter case the structure is 

 founded on- sinking land. It naturally follows that on 



