The Zoologist— March, 1869. 1595 



It is the character of all endosteate animals to be what is called 

 tetrapod or quadruped — that is, either to have four legs or some of 

 the bones required for four legs, even if applied to a different pur- 

 pose, which is very frequently the case: thus in man the fore legs are 

 converted into arms ; in bats and birds into wings ; in snakes they are 

 mere useless rudimentary appendages scarcely protruding beyond the 

 scales; and in fishes they are changed into fins. In the group which 

 I have called Saurians are many snake-like animals, such, for instance, 

 as the blind-worm, which are without external legs, and this has led 

 naturalists to regard them as snakes ; but we must not adopt this view : 

 indeed Nature will assert her prerogative, and show us clearly, from 

 time to time, that we are in error in all our artificial combinations ; 

 thus the blind-worm, whenever it is frightened, irritated or annoyed, 

 will assert its saurian affinities by throwing off its tail, a feat which no 

 snake has the power or the propensity to perform. 



Reptiles are divided into two subclasses : first, immutable reptiles, 

 which after issuing from the egg undergo no change of form or cha- 

 racter ; and secondly, metamorphotic reptiles, which first appear under 

 a fish-like form, breathing water, and finally assume a reptilian form, 

 breathing air;* together with these changes, and necessarily in con- 

 uexion with them, they undergo a complete metamorphosis of internal 

 structure. The immutable reptiles invariably have a harsh and dry 

 dermal envelope, covered with inequalities called plates, crests, scutes 

 and scales ; while that of the metamorphotic reptiles is generally 

 moist, often having what is called a mucous surface. 



Subclass 1. Immutable Reptiles, 



Are divided into four orders, commonly known as Tortoises, Crocodiles, 



Lizards and Snakes. 



Order I. Tortoises (Chelonia), 



Which have no teeth, but a bird-like beak comprised of two corneous 

 mandibles, and in which the vertebral column, the ribs and sternum 

 are greatly dilated, and all their edges soldered or anchylozed together, 

 foi'ming a complete box, in which the animal may be said to reside, 

 as a snail in its shell, and from which it protrudes its head, legs and 

 tail : in some genera the head and fore legs can be protruded, at the 

 will of the animal, through an anterior, the tail and hind legs through 



* See the recently published paper (S. S. 1529). 



