GENERAL CHARACTERS 161 



Gadow as a sub-class equivalent to the other three orders taken 

 together as forming a separate sub-class. The former he names 

 the Phractamphibia from phraktos, armoured, because they 

 possessed calcified or ossified scales embedded in the skin 

 resembling those of primitive fishes, and probably covered ex- 

 ternally by epidermic cornified scutes. The second sub-class 

 he names Lissamphibia from lissos, smooth. We shall consider 

 the Labyrinthodonts in relation to the evolution of the Am- 

 phibia and proceed here to describe the subdivisions of the 

 three Orders of existing forms. 



I. URODELA. 



In the members of this order the primitive elongated form 

 of the body is retained as in lung fishes and in lizards, the 

 trunk being continued without any sudden change of shape into 

 the tail or post-anal region. The tail in the adult continues to 

 serve, as in the larva, as a swimming organ when the animal is 

 in the water. The limbs are somewhat small, usually penta- 

 dactyle, but in many genera the number of digits and the size 

 of the limb are reduced. The pelvic or hip-girdle is transverse 

 to the vertebral column, not extended obliquely backwards as 

 in Anura ; ribs are better developed than in Anura ; the skull 

 is not so much reduced, retaining more separate bones. The 

 tongue is much less developed than in the Anura, and in some 

 of the perennibranchiate or persistent-gilled forms is rudiment- 

 ary. With regard to the condition of the gills, the gill-slits or 

 clefts must be distinguished from the gill-processes. In the 

 Proteidae and Sirenidae the latter persist throughout life, while 

 in the Amphiumidae the gill-processes always disappear in the 

 adult condition, but one pair of clefts in some species remains 

 open. The operculum is vestigial, never completely covering 

 the gills or clefts. 



The Order is divided into four families : the Salamandri- 

 dae, Amphiumidae, Proteidae and Sirenidae. Of these the 

 first is the most highly developed and most terrestrial in the 

 adult state. 



SALAMANDRID/E: Newts and Salamanders. — These have 

 no gills or clefts in the adult. Both jaws are furnished with 

 teeth and the eyes are protected by movable lids. Fore and 

 hind limbs are present, but sometimes reduced. This family 



