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 
