PLATE 6. 



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

 Side view, 300/t 



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



Fig. 12. Period I soon after appearance of ciliary band, long axis, 300^, 



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



Fig. 14. Period I at time of hatching, 384 M 



Fig. 15. Period IT, latter part, long axis 384/x, (partly contracted). 



Fig. 16. Period III, second phase, long axis 540/4 (average). 



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