AMPHIBIANS 3 59 



are permanently aquatic, while the Alpine salamander 

 is viviparous. The surface of the body in living species 

 is smooth or rough, and ordinarily without scales, but 

 there is a group of legless amphibians possessing minute 

 scales in the skin. The skull articulates with the atlas, 

 or first vertebra, by two surfaces or condyles, whereas 

 all living reptiles, and all birds, have only one. The 

 mammals have two condyles, as have the amphibians. 

 Gills are present in the early stages. The red blood 

 corpuscles are oval, and show distinct nuclei. 



3. In Palaeozoic times there existed amphibia, often Palaeozoic 

 of large size, more or less covered with a dermal armor. 

 These animals, known as Stegocephalia, had various 

 fishlike characters, some even having overlapping scales. 

 In several different localities their footprints have been 

 found, so that we know the outward form of the five- 

 toed feet. In some species the anterior feet have only 

 four toes, showing already a reduction of one from the 

 primitive number. These Stegocephalia, though ap- 

 parently well protected, died out entirely at an early 

 period, leaving the race of amphibians to be continued 

 by forms which, although often abundant, never reached 

 the size of the largest of the early group. The groups 

 now living are the following : 



(a) Apoda ("without feet") ; wormlike or snakelike Legless 

 tropical animals, without any trace of legs, 

 and even without pectoral and pelvic girdles. 

 They are thus much modified for their burrow- 

 ing life, yet at the same time they show primi- 

 tive features, the most interesting being the 

 presence of small scales in many of the genera. 

 These scales are imbedded in the skin, and re- 

 call those of the eels. The eyes are little de- 

 veloped. The animal, at least in the genus 



