164 Royal Society. 



But if we venture to indulge our fancy, and consider what would 

 have been the inevitable result of a gradual upheaval of the island, 

 and a corresponding extension of its area until it became vastly in- 

 creased and its original low rounded hills were exalted into moun- 

 tains, it is plain that a great variety of physical conditions would 

 be thereby incurred. One side of the island would be exposed to 

 the full force and direct influence of the trade-winds, the other side 

 would be completely sheltered from them. The climate of these two 

 portions would accordingly differ, and a great difference would be 

 speedily wrought in the character of their vegetation, while that of 

 the elevated central part would undergo a corresponding modification. 

 After some longer or shorter period, we can conceive the island itself 

 being broken up into two portions, separated from one another by a 

 strait, such as divides the North and Middle Islands of New Zealand. 

 This rupture woidd certainly tend still more to affect the existing 

 fauna and flora ; and at the end of another epoch there can be little 

 doubt that the animals and plants of each portion, exposed to different 

 influences, would present a decidedly different appearance, and the 

 eastern and western islands (supposing the separation to have taken 

 place in the direction of the meridian) might each possess its own 

 special form of Solitaire, as the islands composing New Zealand have 

 their peculiar species of Apteryx. 



But it is only in such a case as has just been imagined that consi- 

 derable modifications would be likely to be effected. It therefore 

 seems to be no argument against the existence of such a process as 

 that of " Natural Selection," to find a small oceanic island tenanted 

 by a single species which was subject to great individual variability. 

 Indeed a believer in this theory would be inclined to predicate that 

 it would be just under such circumstances that the greatest amount 

 of variability would be certain to occur. In its original state, 

 attacked by no enemies, the increase of the species would only be 

 dependent on the supply of food, which, one year with another, 

 would not vary much, and the form would continue without any 

 predisposing cause to change, and thus no advantage would be taken 

 of the variability of structure presented by its individuals. 



On the other hand, we may reflect on what certainly has taken 

 place. Of the other terrestrial members of the avifauna of Rodriguez 

 but fevi^ now remain. A small Finch and a Warbler, both endemic 

 (the first belonging to a group almost entirely confined to Madagascar 

 and its satellites, the second to a genus extending from Africa to 

 Australia), are the only two land-birds of its original fauna now 

 known to exist. The Guinea-fowl and Love-bird have in all proba- 

 bility been introduced from Madagascar ; but the Parrots and Pigeons 

 of which Leguat speaks have vanished. The remains of one of the 

 first, and the description of the last, leave little room to doubt that 

 they also were closely allied to the forms found in Madagascar and 

 the other Mascarene islands ; and thus it is certainly clear \\\2ii four 

 out of the six indigenous species had their natural allies in other 

 species belonging to the same zoological province. It seems im- 

 possible on any other reasonable supposition than that of a common 



