Henry L. Bruner 81 
skin, descriptions of which are to be found in the works of Leydig, 72, 
73, Cartier, 74, Todaro, 79, Batelli, 79, and Blanchard, 80. 
One of the most striking characteristics of the skin of the Sauria and 
other reptiles is the great thickness of the different layers. This is 
especially true of the outer stratum of the epidermis, the stratum cor- 
neum. This stratum is a protective covering, apparently a special adapta- 
tion to life in the air. In the vertebrate series it begins as a weak layer 
in the amphibians, where it is associated with glands which moisten the 
skin. In the reptiles the cutaneous glands are wanting and the pro- 
tection of the body is delegated wholly to the stratum corneum, which is 
very thick and compact. In birds and mammals the glands of the skin 
reappear, the skin is protected by special epidermal outgrowths, and the 
stratum corneum is more or less reduced. 
In all of these groups the outer layers of the epidermis are subject to 
a process of regeneration. In the mammals, birds, and some reptiles 
the stratum corneum wears away gradually and is renewed in the same 
way from the stratum Malpighii. In the Sauria, Ophidia, and Amphibia, 
on the other hand, the stratum corneum remains practically intact until 
it is removed, either as a whole or in fragments, by a process of moulting 
which extends over the whole body. This process is associated with a 
pecuhar structure of the epidermis which must now be described. 
Following the classification of Todaro and Blanchard we may distin- 
guish in the epidermis of the Sauria the following subdivisions: 
I. Stratum corneum. 
(1) Pellicula epidermica. 
(a) Stratum sculptum. 
(0) Stratum internum. 
(2) Stratum compactum. 
(3) Stratum relaxatum. 
II. Stratum Malpighii. ‘ 
Of these different strata the pellicula epidermica is especially con- 
cerned in exuviation. As described by Blanchard and Leydig, it includes 
two divisions; a deeper one composed of a single layer of cells, and an 
outer homogeneous stratum sculptum, which is apparently a secretion of 
the underlying cells. This superficial stratum is ornamented with a 
peculiar sculpture which varies considerably in different families. A 
very simple condition occurs in Platydactylus, in which the surface of 
the pellicula is covered with closely crowded tubercles which measure 
about 1 » across the base. They are arranged for the most part irregu- 
6 
