426 A HISTORY OF BIRDS 



leave a large open space along the middle of their cutting edges 

 (111. 47, p. 413). This bird feeds largely upon shell-fish, and 

 according to some the remarkable space just described is 

 caused by the wearing away of the edges of the beak by the 

 hard shells. This explanation, however, will not bear the test 

 of investigation. 



In the great Whale-headed Stork {Balaniceps rex) of the 

 Nile the beak is enormously widened and inflated (111. 47, p. 

 41 3), and a similar modification has been acquired by one of the 

 Night-herons of the Genus Cancrouia, and, strangely enough, by 

 the Shoe-billed Kingfisher {Clytoceyx rex). So far, there appears 

 to be no explanation of the remarkable peculiarity, as it is not 

 known that these birds subsist upon any particular prey different 

 from that pursued by Herons and Kingfishers with normal beaks. 

 The fact that there is a general resemblance in the nature of the 

 prey of the normal Storks and Kingfishers makes this recur- 

 rence of similar types of beaks in the Whale-headed Stork and 

 the Shoe-billed Kingfisher of New Guinea the more extra- 

 ordinary. 



One of the most remarkable ca.ses of adaptation yet brought 

 to light is surely that of the Huia-bird of New Zealand. In 

 this species the beak of the male is short and but slightly 

 curved, while that of the female is rather more than twice as 

 long and much decurved. These birds live on wood-boring 

 grubs, of which the supply is never probably more than suffi- 

 cient. It would seem then that Nature has, so to speak, ensured 

 a sufficiency for each by bestowing upon the one a short beak 

 capable of chiselling away the more decayed parts of the tree, 

 and on the other a long probe, wherewith the desired morsels 

 may be dragged out from holes in sounder wood which would 

 resist the blows of a beak. 



The tongue in birds presents a wider range in structural vari- 

 ations than is to be met with among any other group of verte- 

 brates. As an organ of touch it is used only in a few rare cases, 

 nor does it appear to be commonly used in the selection of food 

 by taste; in Parrots it is certainly so employed, and possibly 

 in some other groups. 



In the majority of birds it is small, provided at the back 

 with a number of small pointed processes directed towards the 

 throat, while at the tip it is horny. In birds which swallow 



