Observations cm the Structure of Feathers and Hair. 33S 



M. Frederick Cuvier, in his second memoir, has commenced 

 his inquiries respecting the development of hairs with the quills 

 of the porcupine, which are, in reality, nothing but long hairs, 

 but whose structure is more apparent, and their producing or- 

 gan more easily examined. 



He here establishes a perfect analogy between prickles and 

 feathers. Both are produced by the same organs, and are sub- 

 jected to the same mode of growth. In the prickles, as in fea- 

 thers, the horny matter is produced by the membrane of a 

 sheath, and the spongy matter by the surface of a bulb ; and it 

 is exclusively from the form of these same organs that the form 

 of the prickles result, which, like the feathers, are produced in 

 a real mould. 



Hairs do not, as was hitherto supposed, form an essential part 

 of the skin. They have a principle of existence of their own, 

 and belong to a system of organs not less remarkable, sometimes, 

 for its complexity than for its development. This system may 

 be associated with the dermis, and be developed in different 

 points of its substance ; but even then, it is not confounded with 

 that organ, but preserves its peculiar nature. 



M. Cuvier concludes from this, that the hair has never hither- 

 to occupied the rank which is due to it in zoological systems. 



He considers the organic system which produces the hairs as 

 analogous to that of the senses, and even as forming part of it ; 

 for in a great number of animals the hairs are a very delicate 

 organ of touch. The slightest touch, even that produced by a 

 hair of the human head, is sufficient to make certain animals, 

 cats for example, contract their skin and make it tremble, as 

 they always do to rid it of light Jx)dies which stick to it, and of 

 whose presence they are apprised by this peculiar sense of 

 touch. 



M. Cuvier concludes his interesting memoir with explaining 

 a disease, the nature of which has hitherto been involved in the 

 greatest obscurity. We mean the Plica. The two singular 

 and distinct affections which are designated by this name, con- 

 sist, the one, of an excessive development of the hair ; the other, 

 of a bloody matter which flows from it when it is cut, it being 

 also even alleged to possess sensibility. A greater activity in the 



