262 



ZOOLOGY 



only of the yolk and for some time after hatching the yolk 

 mass hangs as a lump on the under side of the embryo. 

 Very early a deep groove, bounded by a pair of folds, 

 arises on the edge. This groove is large in front (Fig. 

 245, &). It forms the beginning of the brain and spinal cord. 

 The feathery gills and the beginnings of the appendages 



FIG. 246. Pipa americana. Female with young in pits on its back. 



next sprout out, while the trunk continues to elongate and 

 assume the form of a young salamander (Fig. 245). 



Families of Anura. Of the Anura there are eight or 

 ten times as many species as there are of the Urodela. 

 They are distributed into nearly a score of families. Of 



