432 A HISTORY OF BIRDS 



tip is always horny and generally frayed, especially so after 

 much wear. That is to say, the tongue in birds has an in- 

 herent tendency to become frayed along its edge, and in some 

 cases this tendency has been increased by selection, until the 

 complex structures just described have been built up. 



It is not easy to discover what determines the apparent 

 correlation between the form of the tongue and the nature of 

 the food, which is so often met with ; and any attempt to solve 

 the riddle is met with contradictions. Thus in the Penguins 

 it is long and pointed, and has the upper surface completely 

 studded with long, backwardly directed conical processes, and 

 thereby differ most conspicuously from the Grebes and Divers, 

 and the Auks, Puffins and Guillemots ; all these have similar 

 tongues, long, pointed and smooth, and all, like the Penguins, 

 live mainly on fish. The Emperor and Adelie Penguins of the 

 Antarctic, however, live largely on cuttle-fish, and Crustacea 

 form the staple diet of the Adelie Penguins, according to Dr. 

 Wilson, the naturalist of the Discovery expedition. Yet the 

 tongue in all the species of this aberrant group presents the 

 same peculiar character. Thus the variations in the nature of the 

 diet are correlated with differences in the form of the tongue 

 in the Woodpeckers, but show no such adjustment in the case 

 of the Penguins. The Petrels again differ but little, so far as 

 records show, in the nature of their food, yet in their tongues 

 they present great variations, though in no case does this organ 

 present any very remarkable peculiarities. This fact is the 

 more striking since in the Genus Prion the beak has become 

 remarkably broadened and flattened and provided along its 

 edges with lamellae, recalling those of the Ducks, yet the tongue 

 has not acquired a similar resemblance to that presented by 

 these birds. 



The Alimentary Canal 



It is a point of considerable interest to note that the various 

 modifications presented by the alimentary canal are, in their 

 way, as numerous and as striking as those presented by the 

 beak and tongue. Though there is a manifest resemblance in 

 the structure of the digestive organs, according to whether the 

 diet is of an animal or vegetable nature, yet we meet with a 

 wonderful variety in the details of the several adaptations for 



