274 REPTILES. 



burrows into the mud that a vertical sun speedily bakes into a hard crust. An 

 aperture, however, is left in this clayey cell, by which air is admitted, and 

 therein the mud-fish, enveloped in a thick coat of slime, passes the dry season, 

 rolled up and in a torpid condition. In this state they are dug out of the 

 ground like potatoes and fried like eels. 



FIG. 294. MUD-FISH. 



The Lepidosiren above described, from its scaly covering, seems 

 properly to belong to the class of Fishes, notwithstanding its 

 amphibious capabilities ; but there are numerous creatures de- 

 cidedly reptilian equally provided with both' kinds of respiratory 

 apparatus. 



The number of animals that in their adult state are so furnished 

 is very small ; but there are many which at an early period of 

 their existence are thus organized, and at different periods of their 

 lives possess both lungs and gills. Some of these, when very 

 young, have gills only, and, like fishes, respire water ; but as they 

 advance in age, the gills become obliterated and lungs are deve- 

 loped. 



Such are the frogs, toads, and newts, called, from this circum- 

 stance, Caducibranchiate * A mpkibia, or amphibious animals with 

 perishable gills. In another group the gills are persistent through 

 life, even after the lungs are completely formed ; and, of course, 

 animals so provided can live indifferently either in the air or in 

 water. These are called Perennibranchiate-\ Amphibia, or amphi- 

 bious animals with perennial or persistent gills. 



Animals of this description present many characters in com- 

 mon : instead of being covered with scales, their skin is naked, 

 smooth, and often moist. Their body is either depressed and 

 squat, as the toad and frog, elongated like the salamanders or 

 newts, or worm-like as in the Caecilias. The head is flattened 

 and joined to the body without the intervention of a neck. They 

 have no ribs, and their toes are not furnished with claws or nails. 

 The Amphibia thus distinguished are classified as follows : 



* Caducus, easily falling; branchice, gills. f Perennis, perennial; branchiae, gills. 



