340 



N. YATSU: OBSERVATIONS AND EXPERIMENTS 



Oblique sections yield, as we should expect, asymmetry in regards 

 to the size of blastomeres. Here again it should be remarked that 

 the size of the micromeres of the end-cells is about the same irre- 

 spective of the sizes of their macromcres. 



Inferring from this series of experiments, there seems to be a certain 

 constancy of size in the microments, or at least a tendency towards it. 



e. Experiment V (eleven cases). 



During various periods of the second cleavage the egg was cut horizon- 

 tally. The result was the same as that of the foregoing experiments. 



Fig III 22 represents a case in which, at the time of operation, 

 the cctoplasmic accumulations were found at the macromere pole in 

 preparation for the second cleavage. It is certain that more ecto- 

 plasm was in the nucleated fragment than in any other stage. Yet 

 the micromeres produced from this piece were not larger than those 

 of Fig. II 16. 



Fig. Ill 23 shows a case in which a middle-cell has divided 

 equally instead of giving off a micromere. 



f. Küpe riment VI (five cases). 



The region near the micromere pole was cut off at the 4-cell 

 stage. Exactly as in the forgoing experiments, micromeres of the 

 usual size were formed. 



g. Experiment VII (seven cases). 



At the 2-cell stage one of the blastomeres was cut vertically 

 I Fig. IV 24). This operation caused very little effect upon the mode 

 of cleavage. 



h. Experiment VIII (four cases). 



At the 4-cell stage nucleated portions of the two blastomeres were 

 cut off by a vertical section. The small nucleated fragments per- 



