INTBODUCTION. 



xxi 



Tuatara Lizard. I have not space now to refer to the wonderful characteristics of this living 

 representative of a remotely ancient race ; but I may mention that the Tuatara has been found 

 to possess, concealed under the tough skin of the forehead, the vestiges of a third but now 

 obsolete eye, the functional parts being present, even to the optic nerve ! It has become extinct 

 on the mainland ; and it is a very curious fact that, through long isolation, it has become 

 differentiated in colour in the several islands or groups of islets which it inhabits. With the 

 exception of a green form, exhibiting some structural modifications, which I have dedicated to 

 our great herpetologist, under the name of Sphenodon gicentheri, it has been found impossible to 

 distinguish these forms except as local forms, sufficiently well marked, however, to admit of 

 their being referred to their respective island habitats. What are these, I would ask, but 

 incipient species ? Allowing sufficient time under the existing conditions of life, and reasoning 

 by analogy, each island or group of islets must in the end possess a distinct species of Sphenodon 

 exactly suited to its environment. It is, moreover, sufficiently clear that nothing but the 

 island asylum could have saved this lowly-organised and archaic form from absolute ex- 

 tinction. 



Less fortunate has been another form of New Zealand lizard, the Kawekaweau, whose 

 quasi-arboreal habits of life have prevented its taking advantage of this last refuge. From the 

 accounts of the natives, the Kawekaweau appears to have been a form of Iguana inhabiting 

 the deep forest, and there can be no doubt that it lingered in the land till within the last 

 five and thirty years, when the remnant of its race succumbed to wild pigs and other natural 

 enemies. It is always described by the Maoris as beautifully marked with alternate bands of 

 colour, and reaching at maturity to a length of 2ft. or more.* 



But, although these are good illustrations of the correlation of colour and of the extinction 



of well-established forms in the struggle for existence, I feel that I am rather digressing from 



my subject. 



Closely connected with this subject of assimilative 



colouring is that of the gradual adaptation of structure 



to the conditions of existence. In the ' Birds of New 



Zealand ' I have called attention to some remarkable 



cases of this kind, and notably to that of the Huia 



(Heteralocha acutirostris) — an instance quite unique 



in the whole class of Birds — where the sexes present 



differently formed-bills, specially adapted to their 



habits of life and general economy. Now, on what 



principle, apart from the Darwinian theory, can we 



explain this remarkable sexual difference? 



And to mention another case, that of the Wry-billed Plover (Anarhynchus frontalis) 



is a very remarkable one. In this instance the bird has the bill turned or twisted to the right, 



this asymmetry being admirably adapted to this Plover's peculiar mode of feeding among the 



pebbles of the seashore. In the case of our beautiful Eed-necked Avocet (Becurvirostra 



novcB-liollandice), the curvature of the bill is upwards instead of sideways ; and in both forms this 



marvellous departure from the normal type of a Plover's bill is not only correlated to the 



peculiar habits of the bird, but is congenital, being present in the unhatched embryo. Then, 



THE HUIA. 



:;c It is significant that the Long-tailed Cuckoo (Urodynamis taitensis), whose streaming tail-feathers are hand- 

 somely barred in their whole length with chestnut and black, is also known by the name of Kawekaweau in 

 many parts of the country. In like manner the name Kakariki (indicative of the colour) is applied alike to the 

 Green Lizard and to the Green Parrakeet of our woods. 



