436 EMBKYOLOGY OF THE LOWEK VEETEBKATES ch. 



In the Urodela the least specialized subdivision of the Amphibia 

 the evolution of external form closely resembles that of the Lung- 



Fia. 201. — Development of Ceratodus forsteri. (From Semon — Jn the Australian Bush.) 

 A, stage 32 ; B, 34 ; C, 38 ; D, 41 ; B, 45 ; F, 48. (Magnilication about 6i diameters.) 



fishes. An early stage of such a relatively primitive member as 

 Necturus might readily be mistaken for the corresponding stage of 



