* 



. 



Chap. xiii. Inhabitants of Oceanic Islands. 347 



retaining the same identical form or in some degree modified, appa- 

 rently depends in main part on the wide dispersal of their seeds 

 and eggs by animals, more especially by fresh-water birds, which 

 have great powers of flight, and naturally travel from one piece of" 

 water to another. 



On the Inhabitants of Oceanic Islands. 

 We now come to the last of the three classes of facts, which I 

 have selected as presenting the greatest amount of difficulty with 

 respect to distribution, on the view that not only all the individuals* 

 of the same species have migrated from some one area, but that 

 allied species, although now inhabiting the most distant points, 

 have proceeded from a single area,— the birthplace of their early 

 progenitors. I have already given my reasons for disbelieving in 

 continental extensions within the period of existing species, on so- 

 enormous a scale that all the many islands of the several oceans 

 were thus stocked with their present terrestrial inhabitants. This 

 view removes many difficulties, but it does not accord with all the 

 facts in regard to the productions of islands. In the following 

 remarks I shall not confine myself to the mere question of dispersal, 

 but shall consider some other cases bearing on the truth of the two- 

 theories of independent creation and of descent with modification. 



The species of all kinds which inhabit oceanic islands are few in 

 number compared with those on equal continental areas : Alph. de 

 Candolle admits this for plants, and Wollaston for insects. New 

 Zealand, for instance, with its lofty mountains and diversified 

 stations, extending over 780 miles of latitude, together with the 

 outlying islands of Auckland, Campbell and Chatham, contain 

 altogether only 960 kinds of flowering plants ; if we compare this- 

 moderate number with the species which swarm over equal areas in 

 South- Western Australia or at the Cape of Good Hope, we must 

 admit that some cause, independently of different physical con- 

 ditions, has given rise to so great a difference in number. Even 

 the uniform county of Cambridge has 847 plants, and the little 

 island of Anglesea 764, but a few ferns and a few introduced 

 plants are included in these numbers, and the comparison in some 

 other respects is not quite fair. We have evidence that the barren 

 island of Ascension aboriginally possessed less than half-a-dozen 

 flowering plants ; yet many species have now become naturalised 

 on it, as they have in New Zealand and on every other oceanic island 

 which can be named. In St. Helena there is reason to believe that 

 the naturalised plants and animals have nearly or quite exter- 

 minated many native productions. He who admits the doctrine 



ii 



