REPTILES. 157 



«lass m. — Ucptilia. 



( The Reptiles.) 



A Reptile is a cold - blooded, a,ir - breathing vertebrate, 

 having the exoskeleton developed as horny or bony 

 plates, never as feathers or hair. Limbs, when present, 

 usually adapted for walking, rarely for swimming, 

 scarcely ever for flying. An incomplete double circula- 

 tion, the ventricular septum being usually imperfect or 

 wanting; no metamorphosis; oviparous, rarely ovovi- 

 viparous, the eggs relatively large and usually with a 

 leathery skin. Various important anatomical distinc- 

 tions exist, but the Reptiles are obviously separated 

 from the Birds by the absence of feathers, and from the 

 Batrachians by the presence of scales, and by the absence 

 of gills after leaving the egg. 



Besides the three following orders, a fourth (Ceoco- 

 dilia), is represented by two species Alligator mississip- 

 piensis^ Daudin, and CrococUlus americanus^ Seba, in our 

 Southern States. 



ORDERS OF REPTILIA. 



* Body covered with square imbedded shields ; vent roundish or 

 longitudinal, plaited ; bones of skull soldered together, 

 f Body short, depressed, enclosed between two bony shields, 

 from which the head, limbs and tail may be protruded ; 



no teeth Testudinata, T. 



** Body covered with imbricated scales; vent a cross-slit; bones 

 of skull separate; jaws with teeth. 

 X Mouth not dilatable ; bones of mandible united by a bony 

 suture in front ; limbs 4— rarely rudimentary. 



Lacertilia, U. 



