ASPLANCHNA EBBESBORNII (ROTIFER) 



399 



At the close of the fifth cleavage, the quadrants A, B, and C are 

 composed of two rows with four cells each, and the quadrant D 

 of two rows with three cells each, including the large entoderm 

 cell D, making thirty-one cells in all. The comparative sizes of 

 the cells are shown in the different figures. During the fifth 

 cleavage the cells withdraw toward the exterior (fig. 55) and 



Fig. a Four-cell stage, left side. 



Fig. b Four-cell stage, left side, showing the cleavage spindle in the forma- 

 tion of the ectomere d'. 



Fig. c Six-cell stage, ventral side; shows the anteroposterior extension of 

 cells. 



Figs, d and e Eight-cell stage, ventral and dorsal sides; shows the position 

 of the first quartette of ectomeres similar to that of annelids. This condition is 

 unusual. 



Fig. f Seventeen-cell stage, left side. 



