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Henry L. Bruner 
cula is divided into more or less hexagonal areas, which correspond to the 
cells of the stratum internum. In Phrynosoma I find these areas sepa- 
rated by well-marked ridges, which bear conspicuous prickles at the 
angles of intersection. A similar sculpture has also been observed in 
Moloch, Sceloporus, and Agama. In Phrynosoma the hexagonal areas 
have an average diameter of about 22 » and the prickles may reach a 
height of 8 ». In this form the prickles show their strongest develop- 
ment on the ordinary scales, while they are small or wanting on the 
“horns” and large dorsal spines, where they would probably hinder 
exuviation. On the ordinary scales this difficulty is avoided by the 
inclination of the prickles, those which he on the slopes of the scale 
being perpendicular to a plane passing through the base of the scale, so 
that all of the prickles on a given scale become more or less parallel in 
direction. A similar adjustment is to be observed also in the case of the 
ridges. ‘Those which run parallel with the periphery of the scale become 
unsymmetrical, with the long slope directed toward the base of the scale. 
The different accounts of the exuviation process, as described by Ley- 
dig, 72, Cartier, 74, Todaro, 79, Batelli, 79, and Blanchard, 80, disagree 
in regard to certain details and I shall not attempt a reconciliation here. 
The following facts, however, are well established. In its early stages 
exuviation is a purely physiological process which is characterized by the 
development of a new stratum corneum below the old layer. As a part 
of this growth a new pellicula is formed,—an impervious layer which lies 
next to the old stratum corneum. Owing to its development the old 
stratum is isolated and cut off from its supply of moisture and nourish- 
ment. Gradual dessication follows and the old stratum corneum is 
then ready for the second, or mechanical, stage of exuviation. 
This stage probably begins with the development of the prickles or 
ridges of the new pellicula, which break the contact of the old stratum 
corneum with the new layer. The actual removal is then effected by 
the ordinary movements of the body or by other mechanical means. It 
may be added that the disposition of the ridges and prickles of the new 
pellicula is such as to facilitate the removal of the old stratum corneum. 
In the earlier stages of exuviation an important part is played by the 
blood and lymph-vessels which convey nourishment to the cutis and to 
the Malpighian layer of the epidermis. Such vessels are abundant in 
the subcutaneous layer, whence the arteries run directly to the papille 
and break up into capillaries. The veins and lymph channels which 
drain the papille run for the most part beside the arteries. 
Hyrtl, 38, p. 383, has recorded the observation that the number of 
