672 EEPTILIA. 



in a subsequent page (fig. 340), 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 (t, z) extend nearly the whole length 

 of the abdomen. 



(1865.) The Amphibia above-mentioned, as well as the Menobranchus 

 and the Aocolotl, both animals of very similar construction, preserve 

 their branchiae through the whole period of their lives, and are for this 

 reason denominated Amphibia perennibranchia ta. But there are other 

 genera which, although in the early part of their existence they are 

 equally provided with both gills and lungs, ultimately become suffi- 

 ciently perfect in their organization to enable them to enjoy a more 

 or less complete terrestrial existence, and consequently their branchiae 

 become obliterated as the lungs grow more efficient, until at length no 

 vestiges of the former remain perceptible. These are called A. caduci- 

 branchiata. 



(1866.) The most remarkable examples of the CADUCTBKANCHIATE 

 AMPHIBIA are the Frogs, the Toads, and the Newts, so common in our 

 own country ; and the metamorphosis of these creatures from the tad- 

 pole- 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. 



(1867.) Immediately before leaving the egg, the tadpole of the Sala- 

 mander, or Water-Newt (fig. 329, A), presents both the outward form 



Fig. 329. A 



Larvee of Triton. 



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

 with a broad dorsal and anal fin, the shape of the body, and the gills 

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

 creature to preserve this form throughout its life, the naturalist would 

 scarcely hesitate in classing it with fishes properly so called. 



