JENNINGS: DEVELOPMENT OF ASPLANCHNA HERRICKII. 21 
cell OD", with the undivided aster at its right and slightly behind it 
(Fig. 5). 
By this time the two asters in the cell AB” have completely separated 
and lie upon opposite sides of the enlarged nucleus. Thus the prepara- 
tory stages for karyokinesis are much more advanced in the smaller 
cell, and it would be anticipated that this cell would cleave first. 
The single aster in CD now begins to divide. The process seems to 
be accomplished very quickly, since in a series of nineteen specimens of 
the two-cell stage (each, of course, taken from a different individual) 
only one case was found exhibiting a transitional stage between that 
shown in Figure 5 and that shown in Figure 6. In this specimen the 
single aster had elongated slightly in the direction of the future 
spindle. When formed, the spindle takes an oblique position in the 
cell, extending from right anterior to left posterior. The aster at the 
left posterior end of the spindle is much the larger, in correlation appar- 
ently with the larger mass of cytoplasm surrounding it. The nucleus 
of CD' has now overtaken in its metamorphosis that of AB’; the 
spindles are found in exactly corresponding stages, the chromatin being 
in both arranged in an equatorial plate (Fig. 6). 
Not only are the two spindles not parallel, as shown in Figure 6, but 
they do not lie in the same plane. If the two spindles are viewed 
exactly from the anterior or from the posterior end of the egg, the left 
aster in AB” and. the right aster in OD" are seen to lie more dorsally 
than their mates. Viewed in this direction, the spindles cross each 
other at an angle of about twenty-five degrees. 
As a result of the dissimilarity in the direction of the two spindles, 
the two next cleavage planes, perpendicular to them, will not meet the 
first cleavage plane in a common line. The position and direction of 
the spindle in OD” are such that the cleavage plane cutting OD? 
would probably meet the first cleavage plane to the right of the line 
where the plane dividing 42^ would meet it. Since the right aster of 
CD' is farther dorsal than the left, the plane of cleavage of OD? 
would be inclined to the sagittal plane, — on the dorsal side toward the 
left, on the ventral side toward the right. 
The cleavage of the two cells now follows at almost or precisely the 
same time, the karyokinetie processes being found from this time on in 
the same stage. Ina series of thirty-one eggs from different individ- 
nals, each containing more than one and less than five cells, none con- 
tained exactly three cells. 
An examination of the four-cell stage after the completion of division 
