DEVELOPMENT OF HAIR 



B 





seh 



C 

 -cm 



-sh.a 



elongated and converging slightly above and Ijelow. I )i'. Maurei- 

 has called attention to the remarkable likeness between the 

 embryonic hair when at this stage and the simple sense-organs 

 of lower Vertebrates. Later there is formed below this a 

 denser aggregation of the corium, which ultimately becomes 



the papilla of the hair. 

 This is the apparent 

 homologue of the first 

 formed part of a 

 feather, which projects 

 as a papilla before the 

 epidermis has xmder- 

 gone any modification. 

 Hence there is from 

 the very first a differ- 

 ence between feathers 

 and hairs — a difference 

 which must be care- 

 fully borne in mind, 

 especially when we 

 consider the strong- 

 superficial resem- 

 blance between hairs 

 and the simple barb- 

 Fir,. 2. — Four diagrams of stages iu the development lygg feathers. Still 

 of a hair. A, Earliest stage in one of those mammals 



ia which the dermal papilla appears first ; B, C, D, later the knob of epi- 

 three stages in the deyelopment of the hair in the dermic cells bcCOmeS 

 human embryo, hlb, Hair-bnlb ; era, horny layer 



of the epidermis; foil, hair ■ follicle ; grin, hair- depressed into a tubu- 

 germ; h, hair in D, projecting on the snr- ^^^ structure, which is 

 lace ; miic, Malpighian layer of epidermis ; pp, _ ' 



dermal papilla ; seb, developing sebaceous glands ; lined with cells also 

 .s7/.l, .s7/.2, inner and outer root-sheaths. (After i • -i o j_i 



Hertwi''.) derived from the 



stratum Malpighii, but 

 is filled with a continuation of the more superficial cells of the 

 epidermis. This is the hair- follicle, and from the epidermic cells 

 arises the hair lay direct metamorphosis of those cells ; there is 

 no excretion of the hair by the cells, but the cells become the 

 hair. From the hair-follicle also grows out a pair of sebaceous 

 glands, which serve to keep the fully-formed hair moist. 



Dr. ileijerle^ has lately described iu some detail the parti- 

 ' " Uber die Haare der Saugethieie," Morpli. Jahrh. xxi. 1894, p. .312. 



hlb 



