92 PHILOSOPHY OF ZOOLOGY. 
Hair is found on all the mammalia, whales not excepted ; 
differing greatly, however, in quantity, according to the 
species, but always most abundant on the parts most ex- 
posed, and on these animals which inhabit cold countnes. 
It is found, along with feathers, on different parts of the 
body of birds, chiefly, however, on the head and neck. It 
is absent in the reptiles, fishes, and mollusca; but it may 
be observed on many annulose animals, and even zoophytes, 
in which it acts the part of an organ of motion. 
Of all the substances consisting of animal matter, hair is 
the most permanent, resisting putrefaction for a great length 
of time. According to the experiments of Hatrcuett, it 
consists of gelatine and coagulated albumen. VauquEeLIn 
detected two kinds of oil; one of which was found to vary 
in colour, according to the colour of the hair from which it 
was extracted; black hair yieldmg a black oil; the other 
always white, without regard to the original colour of the 
hair. Hair likewise contains iron, oxide of manganese, 
phosphate and carbonate of lime, silica, and sulphur. 
2. Feathers.—As nearly related to hairs in the animal 
economy, in regard to situation, composition, and purpose, 
we may here take notice of the plumage of birds. 
Feathers may be considered as consisting of the following 
parts: the quill, the shaft, and the web. 
The quill takes its rise, like the hair, in the cellular 
membrane, and passes through a tubular opening m the 
other layers of the skin, which generally exhibit a duplica- 
ture at its base, forming a short sheath. The edges and 
outer side of the distal part of the quill unite with the 
proximal end of the shaft, leaving a small opening in the 
middle of the inner side. 
The shaft consists of a cuticular layer of matter similar to 
the substance of the quill; and a central portion, of a white 
colour ; and with a texture hke cork. The outer side is in 
