356 



CHORD AT A, 



The body is now distinctly elongated and compressed slightly from 

 side to side. 



This stage may (except for the closure of the neuroproe and preco- 

 cious formation of the brain) be compared to the chordula larva of the 



Fig. 254. — The Structure of Frog's Embryo and Tadpole. 



A 



Blastopore. 



Anus. 



Head. 



Stomodaeum. 



Tail. 



Second Gill. 

 First Gill. I Ear. 



Anus. 



Eye. 



Stomodaeum. 

 Sucker. 



C 

 Notochord. Pronephric Duct. 



Brain. 



Stomodaeum. 



Anus. 



Yolk-cells. Liver. Heart. 



Sucker. 



A LongiLudinal Median Section through an Embryo of Frog X 20 (after 

 Marshall). Note the dorsal nerve-tube swollen into a brain anteriorly, the noto- 

 chord below it, and the mass of yolk-cells on the ventral wall of the archenteron. 

 B, Side (right) View of just-hatched Tadpole of Frog X 6 {adnat.'). C, Median 

 Longitudinal Section through a newly-hatched Frog's Tadpole (chiefly after 

 Marshall). 



Airiozoa. As in the case of the gastrula, the chief difference is in the 

 presence of a large mass of yolk containing hypoblast on the ventral 

 wall of the archenteron. 



