JENNINGS: DEVELOPMENT OF ASPLANCHNA HERRICKII. 25 
of the two asters has become central, the other peripheral, as if the cell 
were about to divide into a deep and a superficial portion. This condi- 
tion also is shown in the sagittal section, Figure 7. The difference in 
the position of the asters in d*" and dee is apparently due to simple 
mechanical conditions, — the form of the cell ds compelling the asters 
to take the position which they have. 
At the same time a slight differentiation in the cytoplasm of the cell 
di becomes visible. As previously stated, the fine yolk granules are 
at first distributed uniformly throughout the egg. In this eight-cell 
stage, a slight concentration of the yolk granules in the ventral part of 
the cell d*! may be noticed by careful observation. The condition at 
this time is shown in Figure 7; in the ventral part of d*! the yolk 
granules are a little larger and more numerous. As will be shown, this 
concentration of yolk becomes later much more marked, and its history 
is peculiar. 
A spindle is now formed in d** in the position indicated by the asters 
of that cell in Figure 7, — that is, with a dorso-ventral axis, — thus pre- 
figuring another equatorial cleavage. The spindle is shown in Plate 2, 
Figure 16. 
Immediately thereafter the spindle is formed in ds, and it appears 
that the position of the asters shown in Figure 7 (Plate 1) is not define- 
tive. The asters shift, so that the spindle in d** is dorso-ventral, like 
that in d*!, as is shown in Figure 16. Which of the two asters seen in 
Figure 7 becomes dorsal and which ventral, I have been unable to deter- 
mine. During the formation of the spindle in d*? the cell extends a 
little in the direction of the spindle, as is shown by a comparison of 
Figure 7 with Figure 16. 
Meanwhile, changes have been occurring in the quadrants 4, B, and 
©. As the processes are the same in all three, the quadrant C will be 
selected as a type. 
At first, as described above, the asters separate tangentially, at right 
angles to the axis of the previous spindle (Plate 3, Fig. 17). This 
position is retained for some time, but in a later stage the line connect- 
ing the asters in c has become oblique, as shown in Figure 18, which 
exhibits a side view of the egg of which Figure 7 is a section. The 
asters in c** still retain their original position. 
Now follows the cleavage of the cell d,. This is accompanied by an 
increase of the dorso-ventral extent of the two products, as compared 
with that of the original cell. The division is unequal; the ventral 
cell d5* is much the larger, and retains the whole of the territory con- 
