266 STUDY OF NATURAL HISTORY. 
to purely aquatic animals, like the otter, the seal, 
and the ornithorhynchus; to these the power of 
walking is almost denied, their feet being remark- 
ably short, the toes connected, and the whole 
structure adapted almost exclusively for swimming : 
the second and last structure is restricted to the beasts 
of prey forming the order Fere; the only material 
difference between these and the ordinary feet of 
five-toed quadrupeds, consists in the power they 
possess of retracting and protruding their claws at 
pleasure. The importance of this property to the 
animal is sufficiently obvious, when we consider the 
especial use which is made of them. Strong, and 
peculiarly sharp, they are employed as formidable 
weapons of offence and of defence; with these they 
seize their prey, tear it into pieces, and defend 
themselves from their enemies. We cannot have a 
better or a more familiar example of these habits, 
than in the domestic cat. 
(183.) The feet of birds are no less varied, and 
afford us the means of discriminating the primary 
divisions of the feathered creation, without having 
recourse to any other help. Nor do their differences 
terminate here: under each of the five great modi- 
cations, or types of formation, which may be seen 
in birds, are contained others, still preserving the 
essential character common to all, but deviating 
into minor types, which again point out little as- 
semblages of groups, or of species, more especially 
united among themselves. The most perfect birds 
in creation are of course such as have the greatest 
complexity of structure, and the greatest variety of 
powers. These are unquestionably the perchers ; 
ae 
