CLASS IV. AMPHIBIA. 



MORE OR LESS DISTINCTLY VERTEBRATED. WITH COLD RED BLOOD. HEART UNILOCULAR, OR 

 WITH ONE AURICLE AND ONE VENTRICLE. EXTREMITIES FOUR, TWO OR NONE ; OCCA- 

 SIONALLY DISAPPEARING WITH AGE. SKIN NAKED, DESTITUTE OF SCALES. RIBS SHORT OR 

 WANTING. RESPIRATION BY GILLS OR LUNGS, OR BOTH CO-EXISTENT. FORM IN SOME FAMI- 

 LIES UNDERGOES A COMPLETE METAMORPHOSIS. AQUATIC OR TERRESTRIAL. CARNIVOROUS. 

 EGGS IMPREGNATED AFTER EXCLUSION. 



The Amphibia or Amphibians have, until recently, been treated as an order of Reptiles; 

 but they present so many and such important variations from the character assigned to that 

 class, that modern naturalists have almost unanimously agreed to consider them a distinct class, 

 forming a group allied on the one hand to the Reptiles by the Ccccilida., and on the other to 

 the Fishes by the Sirenidcp. 



As early as 1816, De Blainville published a system of classification, which he had publicly 

 taught in his lectures for several years previous. In this he indicated the propriety of sepa- 

 rating the animals under consideration from the Reptiles. Of these he made a class, which 

 he designated as NudipelUfires or Ichthijoidcs iiiids. This he divided into four orders : 1 . 

 Batraciens, Frogs ; 2. Pseudosauricns, or Salamanders ; 3. Amphibiens, as Proteus, Siren, 

 &c. ; 4. Pscudophydiens, as Csecilia. This was afterwards modified and enlarged in his 

 " Principes d' Anatomic Comparee," published in 1822, when lie designated his third class 

 under the name of Sid)ichthijens. 



The characters assigned to this class must be taken with some limitations. Some of the 

 genera undergo no metamorphosis whatsoever, either in form or respiration ; at least none 

 has hitherto been observed. Nor is the plirase " unilocular heart" literally exact ; for although 

 the auricle is externally single, yet dissections have proved that internally it is in some genera 

 separated into two distinct auricles. 



The Amphibians present such a variety of changes, and such modifications of structure, as 

 to have given rise to many systematic arrangements. From the various systems proposed, 

 we select that of Mr. Bell, as detailed in his admirable work on the British Reptiles, witii 

 such modifications as arc necessary to produce uniformity with the general plan ol this 

 Report. 



