﻿160 ON THE CLASSIFICATION OF BIRDS. 



branaceous web, which extends to their extremities ; by 

 this means it is transformed into a paddle or oar, 

 and it is found that all birds having a foot thus con- 

 structed, are better swimmers than those of any other 

 order. Superiority in diving, however, seems to require 

 a structure of foot more similar to that of the coot ; for 

 in this respect no genus is so highly gifted as the 

 grebes (fig. 87.) 



(138.) The webbed form of foot is the most prevalent 

 in the natatorial order ; but it has three or four modifi- 

 cations which deserve notice. When this structure is ac- 

 companied with a more than usual length of tarsus, and 

 the thigh is naked just above the knee, we may feel 

 assured that the power of walking is superadded to 

 that of swimming. Every one knows how awkwardly 

 a duck walks, or rather waddles, in comparison to the 

 goose : this difference entirely arises from the length of 

 their respective tarsi ; that of the former is very short ; 

 that of the latter much longer. Hence the flamingo, 

 which has the longest legs in the Natatorial order, is so 

 good a walker that it only swims occasionally. It is 

 by this formation that the gulls so materially differ from 

 their congeners the terns, whose very short and weak 

 legs are incapable of traversing the shore in search of 

 those marine animals which the gulls walk after, and 

 collect at each ebb of the tide. We have seen that the 

 grebes, which are the most expert divers, have their 

 hind toe broad and lobed. As an additional proof that 

 such a form, although not essential to swimming, is yet, 

 in some inexplicable way or other, very important to 

 great powers of diving, we need only look to the oceanic 

 ducks of the sub-family Fuligulince, which are only dis- 

 tinguished in external structure from their brethren of 

 the rivers (Anatince) by having their hind toe broad 

 and lobed, which the fresh water ducks have not. It is 

 well known that, while the former dive with great ex- 

 pertness, the latter do so but seldom. 



(139«) * n tne P en gu ms an d the cormorants the 

 hinder toe differs from that of all tha other natatorial 



