ANSERIFOEMES. 



361 



ficial as destroyers of the hosts of voles, mice, and other small 

 mammals, which often increase with alarming rapidity where 

 these rapacious birds have been persistently persecuted. Poultry 

 suffer from the sparrow-hawk, and sometimes the merlin and 

 hohhy ; but the few chicks the two latter take are soon made 

 up for by the good done by their destroying vermin. 



6. Anseriformes. 



DuoKS, Geese, and Swans (Ansbres). 



The Ducks, Geese, and Swans are included in the family 

 Anatidce, which contains as _ 



many as seventeen genera in 

 Great Britain. The Anseres 

 are characterised by the beak 

 (fig. 187) being more or less 

 flattened and covered with a 

 fine tactile skin ; the edges of 

 the bill are furnished with a 

 series of lamellae (L), form- 

 ing a kind of fringe, which 

 acts as a strainer to the mud 

 in which they seek their food. 

 The bill is most sensitive, be- 

 ing abundantly supplied with 

 branches from the fifth cranial 

 nerve. The legs are provided 

 with a three-toed swimmer, the 

 fourth toe pointing backwards, 

 and is free (fig. 188, b). The 

 body of the Anseres is heavy, 

 and densely covered with down 

 beneath the contour feathers, 

 yet these birds are capable of great powers of flight. The males 



-Skull of Duck. 



