CLASS OF FISHES. 635 



tiles. Finally, the nervous system in these animals is but 

 little developed; the brain is small, and the cerebellum 

 is scarcely visible. 



473. Though the class batrachia be not numerous, it 

 has, notwithstanding, been divided into four orders. 



The Anoures, which undergo complete metamorphoses, and 

 which in the adult state have no tail ; these are the frogs, 

 toads, rainettes, pipas, Surinam toad, &c. 



The Urodeles, which preserve the tail, but which in the 

 adult state have four limbs, but no branchiae; the aquatic 

 salamanders or tritons, are examples of this order (Fig 305). 



Fig. 305. Aquatic Salamander. 



The Perenniata, which preserve the branchiae through- 

 out life, and which also have lungs : these are the proteus, 

 the axolotl (Fig. 294), the menobranchus, and the siren. 

 Finally, the ceciliae, which have no limbs, and strongly re- 

 semble serpents. 



Some very singular animals have been lately discovered, 

 which have branchiae and lungs like the siren, but which 

 have in place of feet only cylindrical fins, and which so re- 

 semble fishes in the whole of their organization, that most 

 zoologists have arranged them in the following class : these 

 are the lepidosirens (Fig. 125). 



CLASS OF FISHES. 



474. The fifth and last class of the primary division of 

 vertebrate animals comprises the class fishes. The circum- 

 stance of their being destined to live under water, strongly 

 aifects their whole organization, as is most seen in what 

 regards the apparatus of respiration and circulation ; they 

 breathe by gills, and never have lungs* at any period of their 



* The swimming bladder seems evidently to form a rudimentary lung. E. K. 



