THE PHYLOGENESIS OF VERTEBRATES 31 



Gymnophiona, which still possess scale rudiments, not visible 

 externally. The Stegocephali are of extreme importance, since 

 they were the ancestors both of the present-day amphibians 

 and of the two main reptilian lines, and the survival of a single 

 representative would have been of priceless value to mor- 

 phologists. As it is, however, we are in possession of a large 

 number of fossil remains, many of them extremely well pre- 

 served, and representing four distinct orders ; and further dis- 

 covery along this line may well be expected at any time. Of 

 the soft parts the fossil imprints furnish but little evidence, 

 a lack which must be supplied by the study of the urodeles, 

 undoubtedly their nearest living allies and presumably not very 

 different in the essential internal features. 



These latter animals, though not quite in the direct line 

 of human ancestry, are thus of the greatest importance as the 

 best representatives of what may be called the amphibian 

 stage. The urodeles comprise the tailed amphibians, their 

 most typical representatives being the forms known as sala- 

 manders and newts, also in many sections, unfortunately, 

 " lizards," owing to their superficial resemblance to these 

 latter animals. The more primitive members of this group 

 are often large (10-40 cm.), and the giant Cryptobranchus of 

 Japan, the largest of all living amphibians, attains the length 

 of a meter. 



The Anura, or tailless amphibians, include frogs, toads and 

 tree-toads, and attain their tailless condition in part by a 

 retrogressive development of the caudal region and in part 

 through the excessive development of the ilia and the thigh 

 muscles, a feature connected with their jumping habits. The 

 Gymnophiona are blind subterranean forms, burrowing in the 

 earth like earth-worms, to which they bear considerable re- 

 semblance. They are much attenuated, are without external 

 limbs, and have their bodies clearly marked off into annular 

 segments. They occur only in the warmer parts of the world 

 and consist of but few forms. 



Arising also from the Stegocephali come the reptiles, which 

 have apparently developed along two lines, the one leading to 



