76 



AMPHIBIA. 



INTRODUCTORY OBSERVATIONS. 



The doctrine of continuous affinities could scarcely 

 receive a more striking illustration in the animal kingdom 

 than is afforded by the interesting group constituting the 

 Amphibia of modern authors. Intermediate in their struc- 

 ture, and, in many forms, in their habits and mode of life 

 also, between the fishes and the true reptiles, they bear a 

 still more interesting 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 organiza- 

 tion; a subject which constitutes one of the most impor- 

 tant theories connected with the higher departments of 

 Zoological science. To any person capable of appre- 

 ciating the interest attached to the study of physiological 

 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 exclu- 

 sively 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 



