VII 



EXTERNAL FEATURES OF AMPHIBIA 



437 



Ceratod'U* ami an almost equally 

 an Aiolotl dr Newt about tin- time 

 nt' halchiim. except that in this 

 case there are the well- developed 

 cxicnial 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 (Eana). 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 Hypogeophis (Fig. 202). 

 A conspicuous difference from 

 the condition seen in the Teleo- 

 stonies (Figs. 197, 198, 199) lies 



striking resemblmii < is >lm\vn 



1 



^Ij^^r 



FIG. 202. Embryos of /////''i/''"/' / "' <> ' /W/V/M.S-. 

 (After Braner, 1899.) 



A, B, Cx4 ; DxlJ. (For details of B cf. Fig. 87 f 



< '). /-', eye ; e.jjr, external t;ill ; olf, olfactory 01 -MM. 



