80 AMPHIBIA. 



of the typical Amphibia, I shall here offer a few general re- 

 marks upon this most remarkable phenomenon. In the 

 whole of the tribes of Frogs, Toads, and Newts, or, in other 

 words, in the two orders Anoura and Urodela, the young 

 animal, as it emerges from the egg, and for a considerable 

 time afterwards, exhibits a form and structure essentially 

 similar to those of fishes. The organs of respiration and of 

 circulation differ in no important point from those which exist 

 in that class, and their mode of aquatic progression is abso- 

 lutely identical. At a certain period of their growth a gra- 

 dual change takes place in the structure and function of each 

 of these systems, during which the little pisciform creature 

 is gradually assuming the general characters of the reptile 

 type. I shall here offer a few illustrations of the changes 

 which take place in each of these systems, giving the detail 

 of the various modifications which take place in the different 

 groups, when describing each form. 



The swimming of fishes is effected by the powerful lateral 

 motions of the tail and posterior part of the trunk, and the 

 numerous short oblique masses of muscle, which constitute the 

 greater proportion of the bulk of those parts, are admirably 

 adapted for the performance of these powerful and rapid 

 movements. Such is the use, too, to which the long and 

 powerful tail which belongs to the Tadpole is applied ; and 

 the wriggling motion given to this organ, by which the little 

 animal is propelled through the water, by successive lateral 

 impulses, is similar to that by which fishes are propelled. In 

 the Anoura this is totally removed by absorption, and gives 

 place to the extensive and interesting developement of the 

 anterior and posterior limbs, particularly of the latter, which 

 are equally adapted for leaping with great force on the land, 

 or for a rapid and equal propulsion through the water. In 

 the Urodda, as the Newts, for instance, this original mode 

 of progression continues throughout life, and the feet which 



