CHAPTEE XXXI. 

 THE CAT AS A TYPE OF THE MAMMALS. 



THE highest and last step in the scale of backboned life 

 is the class represented by the duck-bill, the opossum, the 

 cat, and man. In this group hair takes the place of 

 feathers as a covering for the body. They all originate, like 

 the lower animals, from eggs, but the latter are retained 

 within the body of the parent, and the young continue to 

 grow until old enough to be born and fed with milk. 



Let us now examine more carefully than we have perhaps 

 ever done before the common cat, which will serve as an 

 example of this class; and much can be learned by examin- 

 ing even a living cat. 



We see that, as in reptiles and birds, the cat's body is 

 divided into a head, neck, trunk, tail, and four limbs. Its 

 body is closely covered by skin, which is quite loose between 

 the trunk and the elbow, as well as the knee. The skin is 

 clothed with soft glossy fur, each hair of which grows out 

 of a little wart situated at the bottom of a pit in the skin. 

 A hair consists of a root buried in the skin, and the shaft; 

 the substance consists of the pith and rind, outside of which 

 are thin overlapping scales. In the cat the edges of these 

 microscopic scales are smooth, but in the hairs of the sheep 

 the edges of the scales project, so as to form a toothed en- 

 velope. Such rough hairs stick together, forming a felt or 

 wool. We have white and black cats, as well as Maltese, 

 tortoise-shell, and gray cats. This difference of color is due 

 to the coloring matter deposited just within the layer of 

 scales. We also see that pussy's hairs are directed back- 

 wards on the trunk, so that we can stroke her soft fur from 

 the head to the tail, but on her limbs the hairs usually 



