3806 COMPARATIVE ZOOLOGY. 
1. Urodelans have a naked skin, a tail, and two or four 
limbs. Some retain their gills through life, as the Prote- 
us of Austria, Axolotl 
(Stredon) of Mexico, 
and the two-legged 
Mud-eel (Stren) of 
South Carolina. Oth- 
ers drop their gills, 
and always have four 
Fre. 284.—Head and Gills of Menobranchus, Ca- limbs, as the aquatic 
pea Lake: Newts and land Sal- 
amanders."” The fore limbs first make their appearance 
in the tadpole. 
2. Labyrinthodonts, now extinct, resembled gigantic 
Salamanders, except in their complex teeth and exoskele- 
ton of bony plates. 
3. Cecilians have neither tail nor limbs, a snake-like 
big. 485.—rroteus anguiius. Europe. 
form, minute scales in the skin, and well-developed ribs. 
They are confined to the tropics. 
