14 
ON THE CLASSIFICATION OF BIRDS. 
perfection of the class; just as do the Quadrumana 
among quadrupeds. 
(17-) III. The order Natatores indicates the po- 
sition of the swimming tribes ; those whose feet are 
formed almost exclusively for swimming, and who ha- 
bitually live in the water. The duck and the goose 
are famihar examples ; but, to see this structure highly 
developed, we must turn to the cormorant, the pe- 
licans, the grebes, and the puffins. The wings, in 
general, are very short in such as have the feet greatly 
developed, as in the two last mentioned families : but 
sometimes we find this preponderance reversed, for in 
the pehcans the wings are remarkably long and the feet 
weak. In the gulls and terns, again, both wings and 
feet are highly organised, so that it might lead us to 
suspect those birds were the types of the whole order. 
(18.) IV. In the Grallatores, or waders, we have a 
continuation of aquatic, but not of perfect cwimming 
birds. They are chiefly known by their long legs and 
half- webbed toes; a structure which enables them to 
wade sufficiently deep into the water to capture the ma- 
rine animals upon which they feed : in this they are 
greatly assisted by their long, slender, and often flexible 
biU, which they thrust into the mud and sand, and by 
this means burrow, like pigs, for worms and other 
small objects {fig. 4. a). It is clear that their food is 
sucked up, for the mouth itself is (typically) very 
small ; and in this respect they perfectly resemble the 
Trochilida; (fig. 4. b), the most suctorial of aU birds. 
In both these groups, the feathers advance very far 
upon the bill ; and in both we find those birds which 
