PLATE 6. 



Fig. 10. Gastrula, early stage, (a) Looking toward blastopore, (b) 

 Side view, 300/^ 



Fig. 11. Gastnila, late stage, looking toward the blastopore, 300^ 



Fig. 12. Period I soon after appearance of ciliary band, long axis, SOO/j. 



Fig. 13. Period I soon after appearance of groove, long axis 336/^ 



Fig. 14. Period I at time of hatching, 384/^ 



Fig. 15. Period II, latter part, long axis 384,^ (partly contracted). 



Fig. 16. Period III, second phase, long axis 540^ (average). 



