VII 



EXTERNAL FEATURES OF AMPHIBIA 



437 



Ceratodus and an almost equally striking resemblance is shown by 



an Axolotl or Newt about the time 



of hatching, except that in this 



case there are the well- developed 



external gills which were as we 



have seen absent in Ceratodus 



though present in the other two 



Lung-fishes. 



In the case of the Anura it 

 is perhaps premature to make 

 general statements regarding the 

 differences in form which distin- 

 guish them from the more primi- 

 tive Urodela, for different species 

 differ greatly in the size of the 

 egg and its richness in yolk and 

 the great majority of them have 

 not as yet had their development 

 worked out. 



The head-region projects less 

 prominently, sometimes being in 

 its early stages quite flattened 

 out on the yolk (Alytes, Phyllo- 

 medusa) while in other cases the 

 embryo elongates as a whole 

 there being for a time no marked 

 break in contour between head, 

 trunk and tail. In such cases 

 growth in length may for a time 

 be most active ventrally, so as to 

 cause a curvature of the embryo 

 with its concavity on the dorsal 

 side (Bana). In the later stages 

 the tail-region is highly developed, 

 the splanchnocoele being greatly 

 shortened and widened and the 

 head also very broad giving the 

 characteristic tadpole type of 

 larva. 



Particular interest attaches to 

 the development of such types 

 of Amphibia as possess heavily 

 yolked eggs. A good example 

 is afforded by the Gymnophiona 

 such as HypogeopUs (Fig. 202). Flo .202.-Kn 1 i„T,,,„ry/v, ,,„,,/„ ,,/,,.„ 



A conspicuous difference from (After Brauer, 1899.) 



the condition seen in the Teleo- 



H -innNV A, B,Cx4; DxlJ. (For details of B cf. Fig. 87 



StomeS (rlgS. 1\)7, 198, lyy; lies q. E, eye ; e.g, external gill ; olf, olfactory organ.' 



