258 NATATORES. 



veloped, according to the proximity of the species to the typi- 

 cal subfamily Anatina ; in which, as I have before observed, 

 it is carried to the highest perfection, in beautiful accordance 

 with the use that so singular a structure is destined to ful- 

 fil. In the Mergi, which stand at the further extremity of 

 the family, and whose piscivorous habits differ from those of 

 the rest of the Anatidce, this disposition of the edges of the 

 bill becomes much altered, assuming the appearance of dis- 

 tinct hooks pointing backwards, a modification admirably 

 adapted, by acting as teeth, to assist these birds in catching 

 and holding their slippery prey. In this family (and parti- 

 cularly in the typical species), the tongue is very large and 

 fleshy, furnished on its margin and other parts with rough 

 appendages to secure their prey, and probably also to sepa- 

 rate it from the water and mud by which it is often necessa- 

 rily accompanied. The trachea, or windpipe, of the male 

 birds in the three last subfamilies, and in some of the less 

 typical species of Anserina, is distinguished by a singular en- 

 largement or capsule near its bifurcation, differing in form 

 according to the species ; in addition to which a few species 

 display other enlargements in parts of the trachea, as exem- 

 plified in Mergus merganser, Oidemia jusca, Clangula vul- 

 garis, &c. The stomach, or gizzard, of the Anatidce is large 

 and very muscular, and the caecum is of considerable length. 



SUBFAMILY ANSERINA. 

 GENUS ANSER, Bmss. GOOSE. 



GENERIC CHARACTERS. 



Bill as long as, or shorter than, the head ; strait, conical, 



thick; much higher than broad at the base, depressed and 



flattened towards the tip ; entirely covered with a cere, or 



naked skin, with the exception of the nails of the upper and 



1 



