Plate III. 

 Fig. 25 and 2G. Two stages of many-coll blastnla from the side. 

 Fig. 27. Same stage as Fig. 2(5 from below. 

 Fig. 28. Blastopore formation. Crescentic groove. 

 Fig. 29. Later blastopore stage. 



Fig. 30. Very early medullary plate, blastopore remains as a small slit. 

 Fig. 31. Early medullary groove, medullai-y folds forming. 

 Fig. 32. Medullary folds forming. 

 Fig. 33. Later stage than Fig. 32. 



Fig. 34. Caudal end of stage shown in Fig. 33. Closure of neural folds at 

 the caudal end. 

 Figs. 35 and 3G. Later stages of closure of neural folds. 



