ANIMAL ORGANIZATION. 95 



The hair of difTcrcnt animals, and even of different parts 

 of the same animal, is very various in its shape, texture, and 

 mechanical properties. Sometimes, instead of being cylin- 

 drical, the filaments are more or less flattened, striated, 

 deeply grooved, or even beaded. Instead of being solid, 

 they may even be tubular: and they exhibit also the great- 

 est diversity in their length, fineness, tenacity, rigidity, and 

 disposition to curl. All these varieties may be traced to 

 corresponding differences in the form and the relative actions 

 of the component parts of the bulb, namely, the pulp and its 

 capsule.* 



The structure of the organs b}^ which hairs are formed is 

 not easily distinguished, in the ordinary kinds of hair, on 

 account of their minuteness: it is readily seen, however, in 

 the large whiskers of the feline species, and also of the seal, 

 which arc subservient to more extended uses than those of 

 merely covering the body, and which are even supplied 

 with nerves, converting them into instruments of a sense of 

 touch. 



In the quills of the porcupine a still more complicated or- 

 ganization has been detected. Fig. 33 shows a quill with 

 its bulbous root, detached from the body; and Fig. 34, a 

 transverse section magnified. The bulb itself is contained 

 in a distinct cell, shown at a. Fig. 35, which represents a 

 longitudinal section of these organs. This cell contains a 

 portion of fat in which the numerous vessels supplying its 

 pulp and capsule are embedded. The bulb is itself sur- 

 rounded by an outer sheath, s, into the cavity of which, b, 

 there opens a duct, d, proceeding from a small cell or fol- 

 licle, F, lodged in the cellular substance on the outside of 

 the sheath. This upper cell communicates below with ano- 

 ther cavity, c, containing an unctuous matter. During the 

 formation of the quill this unctuous matter is supplied through 

 this channel, and probably enters as an ingredient in its 

 composition. The capsule of the pulp consists of two mem- 



* See F. Cuvier's Memoir on the Formation of the Quills of the Porcu- 

 pine, in the Nouvelles Annulcii du Museum, I. 429. 



