56 MANUAL OF NATURAL HISTORY. 



-Hearts of lungs, to which, rule those which are 

 aquatic form no exception, as they must obtain 

 *heir supply of fresh atmospheric air by coming to 

 the surface of the water. As far as regards man the 

 majority are harmless, though some, as the Croco- 

 diles and Alligators, will occasionally attack him ; and 

 others, as the venomous Serpents, are justly feared, 

 from the deadly nature of the secretion from their 

 poison glands. 



In the following list, the arrangement followed is 

 that given by Dr. Gray in his Catalogues of the Rep- 

 tiles of the British Museum, which seems to be at 

 once a convenient one, and also adapted to the pre- 

 sent extent of our knowledge. The descriptions 

 therefore of the orders and families, have been chiefly 

 condensed from these valuable works. 



III. CLASS.- REPTILES (Reptilia). 



Air-breathing ; cold-blooded ; skeleton bony ; in- 

 tegument clothed with horny plates, or imbricated 

 scales, which are covered with a thin and often de- 

 ciduous epidermis ; lungs cellular ; heart trilo- 

 cular ; no transformation after birth ; reproduction 

 oviparous.* 



I. SUB-CLASS. SCALY-REPTILES (Squamata). 



Body covered with overlapping scales ; skull 

 formed of separate bones ; tongue free, elongate, 

 nicked at tip, often extensile ; vent a cross slit ; 



* With some exceptions, as in the case of the " Viviparous Li- 

 zard " (Zootoca vivipara) of our own country. 



