ORNITHOLOGY OF NEW ZEALAND. 1 5 



individual opinion, so long as it is persistent or constant. For his 

 own part, lie was quite indifferent whether the petrel now exhibited, 

 and which he had named GEstrelata affinis, was regarded as a distinct 

 species or a permanent race, so long as the difference of character 

 was recognised. Admitting the distinction, it was merely a question 

 of convenience with systematists whether to call it by a distinctive 

 name, or to designate it " Species A, variety B." Dr. Finsch 

 considered that this, and (Estrelata mollis, of which specimens were 

 on the table for comparison, were varieties of one and the same 

 species. But Mr. Osbert Salvia, our great authority on Petrels, had 

 unhesitatingly pronounced them distinct species. They, belonged, 

 however, to the same natural group, and were closely allied. 

 Although easily discriminated now, no naturalist of the present 

 day would deny that they had originally sprung from a common 

 parent. This followed of necessity from an acceptance of the theory 

 of evolution. As to the alleged worthlessness of colour as a criterion 

 for discriminating species, he could not agree with Mr. Maskell, 

 because our whole experience was opposed to such an argument. 

 The cases put forward by that gentleman were not in point. For 

 example, the condition of the albino Tui exhibited that evening was 

 due to an accidental absence of the colouring pigment in the feathers. 

 It was merely a lasus naturae, or a freak of nature. However many 

 examples of this kind might be met with, no naturalist of any 

 experience would think of creating a new species out of such material. 

 So in the case of individual peculiarities of plumage mentioned by 

 him. No one would pretend that these were of specific value. Some 

 birds, for example the red grouse (or brown ptarmigan), one of the 

 commonest birds of Great Britain, is so variable in color that scarcely 

 two males can be found with precisely the same markings, and this is 

 likewise the case with the common albatross and some other sea 

 birds. This variability of plumage becomes, then, a character of the 

 species. But if you meet with, say, two forms of sea-gull, one having 

 a black head and the other a white head, breeding true, and 

 presenting this constant character, an ornithologist would, as a matter 

 of course, treat them as distinct species, although he might not be 

 able to discover any other points of difference. On the other hand 

 there is a phase of colouring known as dimorphism, which obtains 

 among some species] of sea-birds — some individuals being dark and 

 others white in one and the same species. Other birds, again, pass 

 through several distinct phases of plumage in their progress from 

 youth to maturity, These adolescent states, and the known instances 

 of dimorphic colouration, do not by any means affect the argument 

 that colour is an important external character in the determination of 

 species. On the main question, however, of manifest structural or 

 organic difference as the surest guide in the differentiation, Sir 

 Walter Buller said that he quite agreed with Mr. Maskell. He 

 would remind the meeting that the study of birds had often to be 

 prosecuted with nothing before the investigat n - but skin and feathers, 

 and that the systematist could only make the most of the materials 

 before him. He did not believe that it would be possible to attain 

 perfection in classification till the internal characters and anatomy of 

 everj r known bird had been as completely examined and illustrated as 

 that of the common rock dove (Col umbo, livia) had been by the late 

 Professor Macgillivray. 



