FOOD AND ITS UTILISATION 95 



birds. In the struggle for existence there has been a 

 utilisation of all manner of openings or vital niches, and 

 thus the direct competition of related species has often 

 been avoided. The mandibles of the crossbill (Loxia) cross 

 one another at the tips, and form an instrument very effective 

 in extracting the seeds from the fir-cones. In the Wry-bill 

 Plover of New Zealand the bill is bent to one side, as the 

 Oyster-catcher's sometimes comes to be, and that is suited 

 for capturing insects and other small fry from beneath loose 

 stones. Professor Newton describes the dimorphic bills 

 of the Huia birds of New Zealand : the short-billed male 

 chisels holes in decaying wood ; the long-billed female 

 probes the crevices in harder wood ; but when he, having 

 discovered a grub in his excavations, is unable to reach it, 

 she comes to his aid. 



(2) It is interesting to note that the most striking features 

 of a specialised bill are not put on until the young bird 

 begins to fend for itself. The curlew has a very long bill 

 in proportion to its body, but there is very little indication 

 of this within the egg. The very young flamingo shows 

 nothing of the characteristic deflection of the bill, and it is 

 not till the young skimmer joins its parents on the sea 

 that the lower jaw grows out far ahead of the upper. We 

 see then that the inheritance of the organism is more fully 

 expressed when new liberating stimuli begin to operate. 



(3) Another point of general biological interest is that 

 similar bills may occur in birds that are not nearly related 

 to one another, e.g. in birds of prey and parrots, in swifts 

 and swallows, in spoonbill and spoonbill-plover. This 

 illustrates what is called " convergence." From different 

 sources similar adaptations have been evolved in relation to 

 similar conditions of life. It is plain that a plastic superficial 

 feature is not of much use in working out a " natural classi- 

 fication." On the contrary, it is apt to lead one astray. 

 One must base conclusions as to affinities or blood-relation- 

 ship on deeper features, such as differences of architectural 

 plan in the skull. 



Adaptations o£ the Tongue.— In many cases the 



