TO THE EMBRYOLOGY OF AMPHIBIA. 11 



circumjacent translucent zone which denotes the extent of the 

 peristomal mesoblast. Now follows the gradual rising up of the 

 embryonic body over the general surface of the spherical egg. 

 First, the posterior portion is raised, and then the head-portiou, 

 carrying with it both the hyoid and mandibular arches which thus 

 come to occupy the lateral and ventral portion as is usual with other 

 forms (Fig. 16). At such stages, some of the mesoblastic somites 

 have already been formed, these appearing first at the neck-region 

 and gradually increasing in number in the posterior direction. The 

 general outline of the pronephric duct may also be recognized 

 externally, on both sides of the foremost two or three somites. 



In this species, the embryo may grow to the perfect larval 

 form within the gradually expanded vitelline membrane. The 

 gradually growing tail may elongate and lie coiled mostly on the 

 left side of the egg, while the head is being gradually raised. 

 Fig. 17 represents a larva, on the eighth day after deposition, 

 forced out of the vitelline membrane by needles. Before being 

 taken out, it could be seen moving about in the slightly distended 

 envelope. The yolk which is now covered by the skin is still 

 quite spherical, and on its dorsal surface the main part of the 

 trunk is wedged in, so that the general aspect of the larva in 

 this stage resembles that of some teleostean embryo. 



The larva, growing further, acquires gradually the usual 

 tadpole shape. Fig. 18 represents a tadpole which, on the tenth 

 day after deposition, had but lately hatched out of the vitelline 

 membrane and was moving about within the partly melted frothy 

 substance. The dendritic gills are already formed, and though 

 small are larger than those of Rana or Bufo at the correspond- 

 ing stage. Blood-circulation in the gill-filaments and the pulsation 

 of the heart may be clearly seen from without under a dissecting 



