REPTIL1A. 539 



(587.) The Siren lacertina, a creature which inhabits the 

 marshes of Carolina, is another amphibious animal, scarcely further 

 removed from the fishes than the last. The Siren attains the 

 length of two or three feet ; it has a body very nearly resembling that 

 of an eel ; but instead of pectoral fins it has two rudimentary feet, 

 each provided with four fingers, its hind feet, the representatives of 

 the ventral fins, being entirely wanting ; it is, moreover, furnished 

 with gills placed on each side of the neck, while internally it 

 possesses two capacious membranous lungs adapted to aerial respi- 

 ration. 



(588.) In the Proteus anguinus, an animal only met with in the 

 subterranean waters of Carniola, the body, of which a figure is given 

 in a subsequent page (Jig. 254), is equally anguilliform ; but the legs 

 are now four in number, although still very imperfectly developed. 

 Its gills are fringes of blood vessels placed externally upon the sides 

 of the neck, and its thin, and delicate lungs (, z) extend nearly the 

 whole length of the abdomen. 



The Amphibia above-mentioned, as well as the Menobranchus 

 and the Axolotle, both animals of very similar construction, pre- 

 serve their branchiae through the whole period of their lives, and 

 are for this reason denominated Amphibia perennibranchiata : but 

 there are other genera which, although in the early part of their exist- 

 ence they are equally provided with both gills and lungs, ultimately 

 become sufficiently perfect in their organization to enable them to 

 enjoy a more or less complete terrestrial existence ; and, conse- 

 quently, their branchiae become obliterated as the lungs grow more 

 efficient, until at length no vestiges of the former remain percep- 

 tible. These are called A. caducibranchiata. 



(589.) The most remarkable examples of the CADUCI BRAN- 

 CHIATE AMPHIBIA are the Frogs, the Toads, and the Newts, so 

 common in our own country ; and the metamorphosis of these 

 creatures from the tadpole, or fish-condition under which they leave 

 the egg, to their perfect air-breathing and four-footed state, is a 

 matter of common observation. We select the Newt (Triton 

 cristatus) as an example of the changes which these amphibians 

 undergo as they advance towards maturity. 



Immediately before leaving the egg, the tadpole of the Salaman- 

 der, or Water-Newt (Jig. 239, A), presents both the outward form 

 and internal structure of a fish. The flattened and vertical tail, 

 fringed with abroad dorsal and anal fin, the shape of the body, and 

 the gills appended to the sides of the neck, are all apparent ; so 



