Buller. — Illustrations of Darivinism. 91 



prefers the simple arrangement in my first edition of " The 

 Birds of New Zealand," limiting the number of species to 

 three, to that of my second edition, fifteen years later, which 

 admits five species of the group. This alteration, however, 

 was not made by me hastily or without full consideration. I 

 believe I have critically examined a very much larger number 

 of Ocydromi than any other working ornithologist, and, 

 although I do not wish to underrate the perplexities pre- 

 sented by the intergrading of plumage, I think I have adopted 

 a very cautious rule of admission. Professor Hutton has 

 recognised at least two more — namely, Ocydromus hectori 

 and 0. ftnschi — and a naturalist given to what is termed 

 " splitting " might easily have increased the number still 

 further. But this is the crux of the whole thing. In this 

 particular instance the species of one naturalist is the sub- 

 species of another, and the " local variety " of a third. What 

 is this but the existeuce of transitional forms under the 

 steady march of evolution ? 



But the question of the great variability of the South 

 Island Woodhens opens up a larger one, which I con- 

 fess myself quite unable to answer. How is it that in the 

 North Island there is but one well-marked species of Wood- 

 hen spread over its entire area, whilst in the South Island, 

 under practically the same conditions of environment, there 

 are at least four species, and possibly more, running into one 

 another in such a way as to puzzle even the most expert 

 ornithologists ? 



The Woodhen genus offers an exceptionally good example 

 for a study of this sort, because, although furnished with 

 ample wings, the quills are soft and useless, and the birds in 

 consequence are flightless. 



To take another instance of the kind : the Kakapo or 

 Ground-parrot {Stringops liabroptilus) has ample wings, and 

 yet it is incapable of flight. The presence of this flightless 

 bird, essentially the same in all respects, in both Islands, pre- 

 sents a difficulty which cannot be ignored. But, then, some 

 species are more persistent in their character than others ; 

 and it may be that the Kakapo, as it existed in different areas 

 before the final elevation, had reached its full development, 

 and has remained station arv ever since. Its markings had 

 become so exactly like the green mosses and other vegetation 

 among which it feeds, thus effectually protecting it from birds 

 of prey, and, in the absence of feral animals, the faculty of 

 flight had become so unnecessary to it, that it is difficult to 

 see in what direction natural selection could operate further 

 to the advantage of the bird. It may be asked why, seeing 

 that the Kakapo is flightless from long disuse of its wings, 

 these members have not been more completely aborted, 



