INTRODUCTORY OBSERVATIONS. 79 



Order II. urodela. 



Body long, slender. Feet always four. Tail long, per- 

 sistent. Ribs very short. Vertebra} numerous and move- 

 able. Respiration at first aquatic by external branchiae, 

 which are never concealed within the chest ; afterwards 

 atmospheric by cellular lungs. Tympanum concealed. 

 Impregnation effected by sexual contact, at least in most 

 instances 



Genera. JSalamandrina, Salama?idra, Molge. 



Order III. amphipneusta. 



Body elongate, formed for swimming. Feet either four 

 or two anterior only. Tail compressed, persistent. Re- 

 spiration aquatic by means of branchiae throughout life, 

 co-existing with rudimentary lungs. Branchiae external, 

 persistent. Eyes with palpebrae. 



Genera. Proteus, Siren, Menobranchus, &c. 



Order IV. abranchia. 



Body long, formed for swimming. Feet four. Cranium 

 solid. Tail compressed. Respiration by means of lungs 

 only. Branchiae none. No metamorphosis known. 



Genera. Menopoma, Amphiuma, &c. 



Order V. apoda. 



Body elongate, slender, anguiform. Feet none. Tail 

 very short, almost wanting. Lungs one larger than the 

 other. (The existence of branchiae at any period of life 



