DEVELOPMENT OF HAIR 





elongated and converging slightly above and Lelow. I )r. 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, wliich 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 iii the development Iggg feathers. Still 



of a hair. A, Earliest stage in one of tliose mammals ■,,,-,■,■, t^ 



ill which the dermal papilla appears first ; B, C, D, later the knob 01 epi- 



three stages in the development of the hair in the rlgvinir' cells bcCOmes 

 human embryo, bib, Hair-bulb ; C7-n, horny layer 



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



germ; h, hair in D, projecting on the sur- j^^. structure, which is 



lace ; vine, Malpighiau layer oi epidermis ; j>2}, _ _ 



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



Sertwto' '"'''' ''"'^ °''*'' root-sheaths. (After ^i^rived from the 



stratum Malpighii, l)ut 

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

 epidermis. Tins is the liair- follicle, and from tlie epidermic cells 

 arises the hair l)y direct metamorphosis of those cells ; there is 

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

 hair. From the hair-fi)llicle also grows out a pair of sebaceous 

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



Dr. Meijerle-' has lately described in some detail the parti - 

 ^ " iJber die Haare der Saugethiere," 3forph. Jahrb. xxi. 1894, p. 312. 



