AMPHIBIA. 325 



inowra. The Urodela are the Tailed Amphibia, the larval 

 ail being retained throughout life : they have a smooth naked 

 kin and a compressed or cylindrical tail, and their vertebrae 

 m both amphicoelous and opisthocoeloiis. To this division 

 lelong the Tritons or Water Salamanders or Newts, and the 

 ,me Land Salamanders. The Anoura are the Frogs and Toads, 

 ir the Tailless Amphibia, which are destitute of gills in the 

 idult state, and always devoid of a tail ; both structures, how- 

 !ver, are present in the larva. Anoura have always two pairs 

 )f limbs, proccelous dorsal vertebrEe with large transverse pro- 

 ;esses, serving the functions of ribs, which are absent. The 

 adiiis and ulna and the tibia and fibula are anchylosed together, 

 rhe posterior limbs, which are the larger, have usually the feet 

 webbed and adapted for swimming. The heart of the Amphib- 

 ian is a stage higher than that of fishes. Although it is com- 

 posed of three chambers, two auricles and one ventricle, in the 

 idult, the larval heart is the same as in fishes. The blood in the 

 idult is received from the lungs in the left auricle and from the 

 body in the right auricle, both emptying into the single ven- 

 tricle, which therefore contains mixed arterial and venous blood, 

 ind this mixed blood is pumped to both the lungs and system. 

 rhe larva has only a two-chambered heart, the blood being 

 driven to the gills, through them, and on to the system ; but as 

 the gills begin to give place to lungs, little branches pass off 

 from the branchial vessels, which unite as the lungs increase 

 md carry part of the blood to the pulmonary sacs. Event- 

 ually the gill supply may cease, the entire blood going to the 

 lungs, when we get a third chamber formed in the heart in the 

 form of another auricle. Other Amphibia have both branchial 

 md pulmonary supplies permanent. The blood - supply then 

 Ming mixed, oxygenation is comparatively slow, and thus little 

 leat is generated, the Amphibia, like fishes, being cold-blooded 

 rertebrates. 



The development of an amphibian is best seen in the frog, 

 rhe spawn, which is deposited in masses in the water, is sur- 



