8 DEVELOPMENT OF HAIR CHAP. 
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 
SUSE 7-200 homologue of une 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- 
Fic. 2.—Four diagrams of stages in the development Jags feathers. Still 
ofahair. A, Earliest stage in one of those mammals i : 
in which the dermal papilla appears first ; B, C, D, later the knob of €pl- 
three stages in the development of the hair in the dermic cells becomes 
human embryo. 6/6, Hair-bulb ; crn, horny layer ; 
of the epidermis ; fol/, hair-follicle; grm, hair- depressed into a tubu- 
germ; h, hair, in D, projecting on the sur- Jar structure, which is 
face ; muc, Malpighian layer of epidermis; pp, ~~ ; ? 
dermal papilla ; seb, developing sebaceous glands; lined with cells also 
sh.l, He inner and outer root-sheaths. (After digniaed er onic 
Hertwig.) An 
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’ has lately described in some detail the parti- 
1 «Uber die Haare der Siiugethiere,”” Morph. Jahrb. xxi. 1894, is cules 
