72 



AMPHIBIA. 



INTRODUCTORY OBSERVATIONS, 



The cloctrine of continuous affinities could scarcely re- 

 ceive a more striking illustration in the animal kingdom tlian 

 is afforded by the interesting group constituting the Amphi- 

 bia of modern authors. Intermediate in their structure, and, 

 in many forms, in their habits and mode of life also, between 

 the fishes and the true reptiles, they bear a still more inter- 

 esting relation to these classes, in that remarkable change 

 which many of them undergo at a certain period of life by 

 which they become transformed from the nature and habits of 

 the former, to those of the latter class ; and thus exhibit in 

 their own individual life a beautiful and complete example 

 of transition of organization ; a subject which constitutes 

 one of the most important theories connected with the higher 

 departments of Zoological science. To any person capable 

 of appreciating the interest attached to the study of physiolo- 

 gical phenomena, the contemplation of an animal which at 

 one period of its life is endowed exclusively with the organs 

 of aquatic respiration, resembling the gills of fishes, with 

 means of locomotion adapted only to a constant residence in 

 the water, and with a digestive apparatus fitted exclusively 

 for the assimilation of vegetable food, assuming by degrees 

 the function of atmospheric respiration, acquiring limbs which 

 are formed for leaping on land with great strength and agility, 

 and manifesting the most voracious carnivorous appetite, will 

 not only excite feelings of the deepest admiration, but ne- 

 cessarily lead to the investigation of the laws by which such 



