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in search of other waters. This is proved by evidence from 

 India, Guiana, Siam, Ceylon ; and some of these fish, as the 

 Anabas scandens, are known to survive for days out of the 

 water. But the facts of greatest significance are furnished 

 by an allied class of Vertebrata, almost peculiar to habitats of 

 this kind. The Amphibia are not, like fish, usually found in 

 waters that are never partially or wholly dried up; but they 

 nearly all inhabit waters which, at certain seasons, evaporate, 

 in great measure or completely waters in which most kinds 

 of fish cannot exist. And what are the leading structural 

 traits of these Amphibia? They have two respiratory 

 systems pulmonic and branchial variously developed in 

 different orders; and they have two or four limbs, also 

 variously developed. Further, the class Amphibia consists of 

 two groups, in one of which this duality of the respiratory 

 system is permanent, and the development of the limbs 

 always incomplete; and in the other of which the branchiae 

 disappear as the lungs and limbs become fully developed. 

 The lowest group, the Perennibranchiata, have internal 

 organs for aerating the blood which approach in various 

 degrees to lungs, until " in the Siren, the pulmonic respira- 

 tion is more extensive and important than the branchial ; " 

 and to these creatures, having a habitat partially aerial and 

 partially aquatic, there are at the same time supplied, in the 

 shallow water covering soft mud, the mechanical conditions 

 which render swimming difficult and rudimentary limbs use- 

 ful. In the higher group, the Caducibranchiata, we find still 

 more suggestive transformations. Having at first a structure 

 resembling that which is permanent in the perennibranchiate 

 amphibian, the larva of the caducibranchiate amphibian 

 pursues for a time a similar life; but, eventually, while the 

 branchial appendages dwindle the lungs grow : the respiration 

 of air, originally supplementary to the respiration of water, 

 predominates over it more and more, till it replaces it entirely ; 

 and an additional pair of legs is produced. This having been 

 done, the creature either becomes, like the Triton, one which 



