1897,] Hair and Feathers. 767 
HAIR AND FEATHERS. 
By J. S. KINGSLEY. 
Birds and mammals, the highest groups of the whole animal 
kingdom, are sharply marked off from each other and from 
all other vertebrates by their tegumentary structures, 
feathers in the one group, hair in the other. Naturally struct- 
ures so characteristic and evident as these have been made the 
subject of numerous investigations, but the more recent and 
more thorough studies have been published almost exclusively 
in German, and hence a summary of these may be acceptable 
to American readers. In the preparation of the following 
account the recent able review by Professor Keibel' has been 
freely used. : 
In the skin of the higher vertebrates two distinct portions 
may be recognized, differing in origin, structure, etc. The 
outer of these layers, the epidermis, arises from the ectodermal 
layer of the embryo, while the other layer, the cutis or dermis, 
has its origin in the mesoderm (mesenchyme). Wien fully 
developed the epidermis consists of a basal layer of cells rest- 
ing on the dermis and receiving nourishment from it. By 
continual growth and consequent division, this basal layer 
produces other cells which come to lie outside it, but these 
more superficial portions, removed from any food supply, do 
not grow or divide, but die, dry up and become hardened into 
a horny cuticular layer which gradually wears away and is 
as constantly renewed from beneath. Outside of this cuticular 
layer comes a third layer, the epitrichium, only a single cell in 
thickness, which is lost in the mammals at a very early date, 
but which persists until a later stage in birds. 
The deeper layer of the skin, the dermis or cutis, is largely 
composed of dense fibrous connective tissue, the fibres of 
which are tightly interlaced, and among them run nerves and 
SON OT OR Lt nh¢ 
! Merkel und Bonnet’s Ergebnisse der Anatomi gs58 
1896. 
