INTRODUCTORY OBSERVATIONS. Te 
carnivorous appetite, will not only excite feelings of the 
deepest admiration, but necessarily lead to the investiga- 
tion of the laws by which such extraordinary changes are 
governed, and of the relations which they bear to the 
theory of continuous affinity before alluded to, and to that 
of progressive development through the whole of the 
animal kingdom. That such phenomena are exhibited by 
the typical forms of this class will be sufficiently esta- 
blished by the slight sketch of their structure, habits, and 
development, which will presently be offered. 
The Ampursta have by many zoologists been considered 
in the light of an order of the class Reptilia ; but the cha- 
racters by which they are distinguished appear to me to 
be sufficiently marked and important to justify their sepa- 
ration as a distinct class. They may be characterised as 
“ vertebrated animals with cold blood, naked skin, and 
oviparous reproduction, and most of them undergoing a 
metamorphosis, having reference to a change of condition, 
from an aquatic to an atmospheric medium of respiration.” 
_* The class has been variously divided into groups, accord- 
ing to the different views of the naturalists by whom they 
have been arranged. The division adopted by many zoolo- 
gists of the present day, according to the mere presence or 
absence of the tail in the perfect state, is not only liable 
to the objections which belong to all merely dichotonous 
arrangements, but appears to be far less natural and less 
consistent with the physiological characters of the groups 
than that which is derived from the absence or presence 
and the duration of the branchie. Thus the Frogs and 
Toads, which in the adult state have not the vestige of a 
tail, and the Salamanders and Tritons, which retain that 
organ through life, all agree in the early possession of 
branchiz, which are subsequently lost and replaced by true 
