DEVELOPMENT OF HAIR 



elongated and converging slightly above and below. Dr. Maurer 

 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 under- 

 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- 



FiG. 2. Four diagrams of stages in the development \QQQ feathers. Still 

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



in which the dermal papilla appears first ; B, C, D, later the knob ot epl- 



three stages in the development of the hair in the (Jgj- m i c cells becomes 

 human embryo, bib, Hair-bulb ; crn, horny layer 



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



germ; h, hair in D, projecting on the sur- k structure, which is 

 face ; ?MC, Malpighian layer of epidermis ; pp, 



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



sh.l, sh.2, inner and outer root-sheaths. (After j j n .-, 



Hertwig.) 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 by 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. Meijerle 1 has lately described in some detail the parti- 



1 " ITber die Haare der Saugethiere, " Morph. Jahrb. xxi. 1894, p. 312. 



pp 



