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 would 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 Apteryz. 
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 few 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 that four 
out of the s¢a 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 
