The Development of the Frog 47 



before the stomodaeum. Before the neural 

 canal has been completely closed a small de- 



PN 



so 



FIG. 17. LONGITUDINAL VERTICAL SECTION THROUGH THE AN- 

 TERIOR END OF A TADPOLE SHORTLY AFTER THE TIME OF HATCHING. 



LENGTH OF THE TADPOLE, 8 MM. (After Marshall.) 



A, auricle of heart. B F, fore-brain. BH, hind-brain. B M* mid-brain. 

 C', pericardia! cavity. C V, vesicle of cerebral hemispheres. /, infundibulum. 

 Z,, liver. jV, notochord. O, depression of floor of fore- brain from which the 

 optic vesicles arise. O , oesophagus. P, pituitary body. P N, pineal body. 

 S, central canal of spinal chord. SD, stomodaeum. 7', truncus arteriosus. V y 

 ventricle. I", yolk-cells. 



pression is seen below the blastopore (Fig. 1 2, 

 PD) ; this is the beginning of the anal in- 

 vagination. At the same time a diverticulum 



