SYSTEMATICALLY ARRANGED. 107 



mant and inactive lungs are gradually evolved, and come into play ; 

 and the four limbs are developed. The aquatic is now transformed 

 into a terrestrial animal, — adapted essentially for a terrestrial exist- 

 ence : for although the frog be an expert swimmer and diver, and 

 is enabled, from the peculiarities of its respiratory function, to re- 

 main a considerable time beneath the water, still it must, of neces- 

 sity, have frequent access to the atmospheric air ; and would shortly 

 perish, like any other terrestrial animal, if submerged in that fluid, 

 the presence of which was essential to its existence in the tadpole, 

 or larva, state. 



Here, then, we have not only an adaptation of peculiar organs 

 to a peculiar state of existence ; but a perfect and most striking 

 change in the adaptation of the former to the altered circumstances 

 in the mode of life. There is assuredly nothing in the transforma- 

 tions of Lepidopterous Insects, astounding as those transformations 

 really are, nothing more wonderful, or unanswerably demonstrative 

 of design and providence in the works of creation, than this. I envy 

 not the constitution, the feelings, or prospects, of that mind, which 

 can contemplate the metamorphosis of the aquatic and fish-like 

 tadpole into the air-respiring and reptile Frog, without a deep 

 conviction that these are wonders which an Omniscient Spirit could 

 alone have projected, which an Almighty Hand could only have 

 achieved. 



On these peculiarities in the structure and functions of the respi- 

 ratory organs, the separation of the animals wherein they are exhi- 

 bited, from the Reptiles, with which they have been until very 

 lately confounded, principally rests. This peculiarity, however, the 

 student will bear in mind, exists only in the early life, — or what 

 may be called the larva state, — of our British Amphibia, Yet 

 there are several exotic genera which, as the Proteus and the Siren, 

 are permanently provided with both gills and lungs, and conse- 

 quently capable of respiring, with equal facility and effect, in water 

 and in air. These are, rigorously speaking, the only real Amphibia ; 

 as permanently and equally fitted for both an aquatic and terrestrial 

 life.* The former, as possessing only temporary gills, are conse- 

 quently arranged under the Sub- class, Caducibranchia ; and the 

 Proteus and Siren, as permanently provided with these breathing 

 organs, under the Perennibranchia,\ of modern Amphibiologists. 



* 'Ap<p), on all sides, j9£w, life. 



f From compounds of the Latin Caducus, deciduous, and Perennis, perma- 

 nent, with the substantive, Bronchia, gills. 



