The Development of the Frog 47 



before the stomodseum. 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 3/, mid-brain. 

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

 L, liver. N, notochord. 0, depression of floor of fore-brain from which the 

 optic vesicles arise. O E, oesophagus. />, pituitary body. P N^ pineal body. 

 5, central canal of spinal chord. 6"Z>, stomodaeum. T, truncus arteriosus. K, 

 ventricle. 1", yolk-cells. 



pression is seen below the blastopore (Fig. 12, 

 P D) ; this is the beginning of the anal in- 

 vagination. At the same time a diverticulum 



