18 



ART. IT. X. YATSU. 



and became a perfect larva. 

 For drawing any conclusion 

 tlie cases are altogether too 

 few, yet judging from the 

 result of Series J the cut 

 does not seem to affect 

 embryogénie development 

 much. In still another 

 case a portion near the 



vegetal pole was cut off at the 4-cell stage by a horizontal section, 



and a perfect pilidium was produced. 



Fig. 16. 

 Diagrams showing the cut in Series M. 



Series N. Removal Experiment at the 5-cell Stage. 



One blastomere was removed at the 4-cell stage and the 

 remaining three were allowed to develop into pilidia. Five 

 larvae were obtained. Except one, which was slightly defective, 

 all were perfect. The blastomeres tend to open on one side 

 but they close up during the course of development. 



Series 0. Isolation Experiment at the 4-ceIl Stage 

 into a Group of two Blastomeres. 



The blastomeres were separated in twos at the 4-cell stage. 

 Five pilidia were obtained and all of them were normal as might 

 have been expected from the experiments of Series G, H and L. 



Series P. Isolation Experiment at the 5-cell Stage 

 into a single Blastomere. 



The blastomeres of the 4-cell stage were separated from one 

 another by means of a knife or Ca-free sea-water. Twenty-seven 



