586 LOCY. 



Figs. 19 and 20. Side view of two heads of embryos with open neural groove 

 to show the external appearance of the optic vesicle. 



Fig. 21. Embryo of same age as Fig. 13 viewed obliquely from above. 



Fig. 22. Side view of embryo of the same age (with broadly open neural 

 groove) to show the external appearance of the optic vesicle and the other vesicles 

 behind it. 



Fig. 23. Embryo after partial closure of the neural groove. Showing two 

 openings, an anterior and a posterior one, into the neural canal. 



Fig. 24. Somewhat older specimen with head broken off. Showing three 

 openings (smaller than those in the preceding embryo) into the neural canal. 



