132 



N. YATSU. 



experiment was begun at the end of my stay at Harpsvvell, and 

 I can give here only four cases. 



(i) The egg was cut along AB ($A) and a perfect pilidium 

 was produced which is represented in 5 C. It is important to ob- 

 serve that, in spite of cutting off the cytoplasm from the animal 

 pole, the apical organ has developed undisturbed. 



(2 and 3) The eggs were cut along CD (5/4). From each 

 blastomere arose a pilidium with one ciliated lobe and no apical 

 organ. The cases are too few to draw any conclusion, but the 

 importance of the cytoplasmic bridge connecting the blastomeres 

 and of constriction of the first cleavage upon the arrangement of 

 organ bases, is not to be overlooked. 



(4) The egg was cut along EF ($A). From the left half a 

 perfect but dwarf pilidium resulted. This is a case worth de- 

 scribing, because the egg neither rounded up, as is usually the 

 case, nor divided into two unequal halves, but soon after the cut 

 surface was closed, the right half gradually increased in size ac- 

 companied by the decrease of the left half, and thus the egg was 

 divided into two equal blastomeres. 



SERIES E. 



Development of the Blastomeres Isolated at the Two-cell Stage. 



The blastomeres of eight eggs were separated at the two-cell 

 stage when the cytoplasmic bridge had disappeared and the blas- 

 tomeres had assumed a spherical form. From every blastomere a 

 normal pilidium was developed. Some were about half the nor- 

 mal size, while some, for reasons that I cannot explain, were very 



