24 



COMPARATIVE ANATOMY 



The dermal papilla is thus always the primary part of the 

 scale which causes the elevation of the epiderm (Fig. 18). At 



Horny papilla. 



Mdlpighian layer Horny layer 

 Papillae. of eviderm. of epiderm. 



FIG. 18. SECTION OF SKIN OF A YOUNG TORTOISE (Testudo grcaca), FROM THE 



XECK. 



the same time, a marked proliferation of the epiderm occurs, at 

 first uniformly and later in different degrees on the upper and 

 lower surfaces of scales when they overlap one another (Fig. 19). 



Loose connective Spitrichous 

 tissue layer. layer. 



Horny layer (scale). 



Piyment layer. 



Muscles. 



FIG. 19. SECTION OF SKIN OF LIZARD (Lacerla agifi*). 



As in Amphibians, a periodic casting of the superficial part of 

 the many- layered horny epiderm occurs, either in shreds, or 



