502 Mr. N. A. Vigors on the Natural Affinities 



Jnser, Bernicla, and Cereopsis, until it is superseded by the short 

 necks of the more oceanic Jnatidce, which exhibit all the ex- 

 pansion and capaciousness of throat observable in the typical 

 Natatores. 



The distinctively marked character of the lobated hind toe, 

 which prevails among the latter groups of the family we have 

 just quitted, conducts us to Podiceps, Lath., that commences the 

 family of Colymbidce, where the same character is strongly de- 

 veloped. The difference between the bills of the types of these 

 two families is softened down by the intervention of that of 

 Mergus, which is intermediate between the broad and depressed 

 bill of Anas and the narrow and sharp-pointed bill of Podiceps. 

 This last genus, in conjunction with Colymbus, Linn., from which 

 it differs chiefly in the construction of the foot, composes the 

 family of Colymbidce. These two well-known groups, differing 

 but little among themselves in external characters, form one of 

 those normal groups of the order, where a deficiency is exhibited 

 in the powers of flight by the shortness of their wings, and in the 

 faculty of walking by the backward position of their legs. These 

 deficiencies in the groups before us are compensated for by their 

 capability of remaining for a length of time under water, and by 

 their superior powers of diving. For this latter purpose the 

 structure both of their wings and legs is admirably adapted : the 

 former by their strength assisting them as oars imder water, and 

 by their brevity not interfering with their progress ; the latter, by 

 their compressed and sharpened edge offering no resistance to the 

 water as they are drawn up to effect the stroke which accelerates 

 the movements of the bird. From their superiority in these cha- 

 racters and powers, the birds themselves have obtained par excel- 

 lence the name of Divers. In these particulars we may observe 

 them to be united to the Alcadce which succeed them, and from 

 which they are chiefly separated by the presence of the hind toe, 



conspi- 



