130 REPTILIA. 



CLASS III. REPTILIA* 



TEGUMENTARY SYSTEM. 



THE external coverings of Reptiles have not been so closely inves- 

 tigated, especially in an histological point of view, as those of Mam- 

 malia, Birds, and Fishes. 



The naked Amphibia, such as the Frogs, have a smooth slippery 

 skin covered by a tesselated epithelium, which is continually being 

 shed in large irregular patches, or shreds. The nuclei of the epithe- 

 lial cells are usually distinctly visible in the layers thus thrown off. 

 Simple glandular follicles, closely aggregated, and more or less 

 numerous, with frequently star-shaped or ramified pigmentary cells, 

 are found beneath this epithelial layer. The skin surrounds but 

 loosely the muscles of the body, and numerous spaces for lymphatic 

 vessels are found beneath it. It is exceedingly vascular and richly 

 supplied with nerves, and is therefore very sensitive, and capable of 

 producing when irritated the most lively reflex phenomena. The 

 small slightly-developed glandular follicles of the integument attain 

 so large a size in the Toads, Frogs, and Newts, as to effect a transi- 

 tion to the more composite forms of glands. In some instances, as 

 in Salamandra, Triton cristatus, &c., small pyriform follicles, either 

 solitary or aggregated, extend over a great part of the back, or form, 

 as in the Toads and Newts, a large warty protuberance behind the 

 ear, from which an acrid milky fluid may be readily expressed, the 

 excretory ducts of the several sacs being readily recognised during 

 this operation. 



* Class REPTILIA. 



Sub-Class 1. Reptilia squamigera. 

 Order I. SAURIA. Ex. Crocodile, Lizard, Chameleon. 

 II. CHELONIA. Ex. Tortoise, Turtle. 

 III. OPHIDIA. Ex. Rattlesnake, Boa, Viper. 



Sub-Class 2. Reptilia nuda s. Amphibia. 

 Order IV. B.TH.CH,, 



( Derotremata. Ex. AmpJiiume, Menopome. 



V. ICHTHYODEA. -?Perennibranchiata s. Proteidea. Ex. Proteus, Siren, 

 ( Axolotl. 



