YELLOW-BUMPED PARRAKEET. 
11 
explain not only the extinction but the origin of species. Mr. Wallace 
(Proceed. Linn. Society, August, 1858, p. 57,) assumes that a variety 
may arise in a wild, species, adapting it to changes in surrounding 
conditions, under which it has a better chance of existence than the 
type-form from which it deviated, and of which it would take the 
place. Mr. C. Darwin had, previously to Mr. Wallace, conceived the 
same application of this principle, which he illustrates in his work On 
the Origin of Species, by many ingenious suppositions, such as the fol- 
lowing: — f To give an imaginary example from changes in progress on 
an island, let the organization of a canine animal which preyed chiefly 
on rabbits, but sometimes on hares, become slightly plastic; let these 
same changes cause the number of rabbits very slowly to decrease, 
and the number of hares to increase; the effect of this would be that 
the fox, or dog, would be driven to try to catch more hares; his 
organization, however, being slightly plastic, those individuals with the 
lightest forms, longest limbs, and best eye-sight, let the difference 
be ever so small, would be slightly favoured, and would tend to live 
longer, and to survive during that time of the year when food was 
scarcest; they would also rear more young, which would tend to inherit 
these slight peculiarities. The less fleet ones would be rigidly destroyed. 
I can see no more reason to doubt that these causes in a thousand 
generations would produce a marked effect, and adapt the form of the 
fox or dog to the catching of hares instead of rabbits, than that 
greyhounds can be improved by selection and careful breeding. Yet 
this condition of things, if followed out to its full consequences, 
seems to lead only to my original inference, namely, an extinction of 
species; for, when the hares were all destroyed the long-legged dogs 
would perish. At most there could but be a reversion to the first 
form and conditions. For, as the hares decreased in number, that of 
the rabbits would increase; the changes of organization that fitted the 
dogs for catching hares being such as would detract from their power 
of unearthing rabbits. A variety with a shorter and stronger foot might 
arise, and would be the first to profit by the preponderance of the 
burrowing rodents. The individual dogs with the strongest and shortest 
limbs, let the difference be ever so small, would be slightly favoured, 
live longer, rear more young inheriting the rabbit-catching peculiaiities; 
the less fossorial varieties would be rigidly destroyed, etc. It is an 
argument in a circle.'” — (Owen: Palceontology , p. 435.) 
Exactly so: and if in the foregoing somewhat lengthy extract we 
read Parrot instead of ‘dog’ , and blossoms and seeds instead of hares 
and rabbits’, we have the case of our Psittacidce to a nicety, and 
equally untenable, the only real explanation of the origin of species 
