OF THE CLASS MAMMALIA. 



225 



390. Integuments. In a certain number of mammals the 

 skin is naked that is, it is not secured from harm by any 

 protecting organs, but in the greater number we find hairs; 

 and so constant is this fact, that M. de Blainville proposed to 

 name them piliferes, in contradistinction to penniferes and 

 squammiferes that is, birds and fishes. 



The hairs are formed by small secreting organs lodged in 

 the skin, or immediately beneath it. Each hair is formed in 

 a small ovoid pouch, with white resisting walls, communi- 

 cating externally by a small opening ; this pouch is termed 



Fig. 172. The Porcupine. 



the capsule. The interior of this cavity is lined by a mem- 

 brane, sometimes reddish, sometimes diversely coloured, and 

 considered to be a continuation of the rete mucosum of the 

 skin ; and at the lower part of this capsule is a conical papilla 

 or bourgeon, which receives the nerves and bloodvessels, and 

 which forms the hair. The substance forming the hair has 

 the greatest analogy to dried mucus. Under the microscope 

 the hairs seem to be formed of small cones or cornets, jointed into 

 each other ; but generally they resemble a simple horny tube, 

 Q 



