YELLOW-BUMPED PABBAKEET. 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 suppositious, such as the fol- 

 lowing: — 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 peculiarities; 

 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 c 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 



