ORIGIN AND CHARACTERISTICS 45 



alimentary and genital organs and the* circu- 

 lation. The Digestive System embraces the 

 Alimentary Canal and its various glandular ap- 

 pendages either embedded in its walls, or like 

 the Liver and Pancreas connected with it by 

 special passages. Its function is to prepare the 

 food, partly by mechanical and partly by chemi- 

 cal processes, and to absorb the nutritive fluid 

 (Chyle) by aid of the lymphatic vessels. The 

 first organ of digestion is the Tongue, which 

 is subject to an immense amount of modifica- 

 tion, often- similar in distantly related groups, 

 due to correlation with special modes of ob- 

 taining food. In birds the tongue can scarcely 

 be regarded as an organ of taste, although in 

 many species it is of the greatest use in securing 

 prey, and in most is subservient to deglutition. 

 A brief description of some of the principal 

 types of tongue may not be devoid of in- 

 terest. It certainly reaches its greatest de- 

 velopment in birds of the Duck tribe (as well 

 as in the Flamingoes), whilst in the other 

 extreme it becomes reduced to a mere 

 nodule in the Pelicans and Gannets, in some 

 of the Herons, Storks, Hornbills, Hoopoes, 

 Kingfishers, Goatsuckers, Petrels, and Ratitae 

 bii'ds. In Raptorial birds the tongue is short, 



