136 Transactions. — Zoology. 



species of birds, that individuals present two different styles 

 of coloration, or ' phases,' presumably more or less inde- 

 pendent of geographical distribution, present or past, or, in 

 fact, of any apparent cause whatsoever. The difficulty in find- 

 ing a plausible theory is much increased by the circumstance 

 that there are nearly as many kinds of dichromatism as there 

 are dichromatic species." Among the examples put forward 

 by him is that of the dark and white forms of Ossifraga 

 gigantea. In this I think he is mistaken. I have, from time 

 to time, recorded seven examples of the White Nelly from New 

 Zealand waters. Of these only two were absolutely pure 

 albinoes. One of them, which I obtained at Waikanae, about 

 forty miles up our west coast, and presented to the Colonial 

 Museum, was of snowy whiteness, without blemish of any 

 kind, even the legs and feet being whitish, whilst the bill was 

 yellowish horn-colour. The other, which is almost as pure, 

 was obtained at sea, about ten miles north of Milford Sound, 

 and presented to me by Captain Fairchild. All the other 

 examples are more or less marked with dark feathers, scattered 

 irregularly over the entire body. There are certainly two 

 phases of the dark plumage — the one uniform slaty-grey, the 

 other paler grey with whitish cheeks and throat — but these 

 differences are in my opinion attributable to age and sex. 



In addition to "dichromatism" there is what is termed 

 " trichromatism," where, apart from the normal form, there 

 are two different-coloured phases, although this phenomenon 

 appears to want confirmation, the evidence in support of it 

 being incomplete. If the theory be true it may help to ex- 

 plain the formation of new species, — the original stock dying 

 out in the struggle for existence, and the dichromatic phases 

 becoming stereotyped into two invariable forms or species, 

 separated geographically but still identical in structure. Dr. 

 Kingsley mentions an example brought forward by Mr. 

 Bidgway, that of the Scarlet and the White Ibises (Guara rubra 

 and G. alba), of which he remarks that they are now so dif- 

 ferent in colour that probably no one would deny their specific 

 distinction, though structurally so alike that a specimen of 

 the white one dyed scarlet would be indistinguishable from 

 G. rubra; and he concludes with this observation : "The ques- 

 tion which finally impresses itself upon the inquirer, in view 

 of the above facts, is this : Are not the two or three phases 

 of dichromatic or trichromatic species 'incipient species,' the 

 final state of which will be that of the White and the Scarlet 

 Ibises? The subject is one of the most perplexing, and conse- 

 quently most interesting, questions in modern ornithology. It 

 shows what we know, and particularly what we do not know; 

 it shows that ornithology means more than a mere description 

 and naming of birds; that one of its aims is to contribute to 



