384 MANUAL OF ELEMENTARY ZOOLOGY 



and an inferior vena cava, but the Dipnoi have what are 

 at least very passable attempts at both of these. Like the 

 fishes, however, Amphibia have only ten cranial nerves, their 

 eggs are without shells, they lack the embryonic membranes 

 known as the amnion and allantois (p. 506), and they start 

 life as gilled larvae. They have usually no exoskeleton. 

 Besides the sturdy, long-legged, tailless animals, known as 

 frogs and toads {Anura), the long-bodied, short-legged, 

 tailed Newts, or Urodela, belong to this group, and it also 

 comprises the Gymnophiona — small blind, limbless, and tail- 

 less creatures, which live like earthworms in the soil of 

 warm countries. The Gymnophiona have rings of small 

 scales embedded in the skin, recalling those of the Teleostei, 

 but probably really the last remains of a bony armour 



Fig. 277. — Ccecilia, one of the Gymnophiona. 



an, Anus, in an enlarged view of the underside of the hinder end. Note the 

 absence of taii. 



which existed in certain extinct newt-like Amphibians 

 (Stegocephalt) and may perhaps be compared to the 

 scales of ganoids. Upon the head of the Stegocephali 

 some of the bony plates became a part of the skull, which 

 was in other respects more highly developed than that of 

 the frog. The skulls of Amphibia show a progressive 

 simplification in Gymnophiona, newts, and frogs. 



The reader will find on pp. 499-502 of this book an account 

 of the fish-like arrangement of the arteries of a tadpole, and 

 their relation to that of a frog. Here it may be added 

 that in various newts more than one pair of aortic arches 

 persists in the adult. In the Common Newt {Molge) the 

 ductus arteriosus remains well developed, giving an addi- 

 tional pair of arches (the pulmonary) ; in the Salamander 

 the missing third branchial arch, lying between the two 



