610 
T. H. MORGAN 
the normal nuclei (plate 2, fig. T) these seem out of all proportion. 
Also during the construction phase of these nuclei the chromatin- 
mass often appears condensed. It is difficult to explain this result 
unless it means that some constituent of the nucleus is lost in the 
centrifuged egg or at least that less of it passes on to the spindle. 
Possibly the conditions shown in fig. 31 may account for the result. 
This egg was centrifuged as the two nuclei re-formed. The 
watery fluid that collects at this time is carried to the oil cap. Its 
loss may account for the reduced size of the nuclei. 
In a few eggs, that were centrifuged when the spindle was well 
developed, I have noticed a remarkable condition in the center of 
the aster. As shown in plate 2, fig. S, a yellow ring, that stains 
like yolk, lies around a central granule. Whether in reality one 
or more yolk granules have passed into the more fluid (?) center of 
the aster and been caught there, or whether we are dealing with an 
artefact, I can not state. But the result is so peculiar that it 
seemed worth while to draw attention to it. 
The movements of the materials that take place during the 
first cleavage can be studied both in the living egg and in sections. 
When the cleavage passes through the oil pole the oil is drawn 
down along the plane of division as far as the former center of the 
egg. Similarly for the yolk as seen in sections in plate 2, fig. U. 
This egg divided while on the centrifuge. Doubtless the forces 
that produce division sufficed to carry in the yolk against the cen- 
trifugal force acting in the opposite direction. 
If the eggs are allowed to complete the first division before they 
are centrifuged, each cell is stratified into three layers, plate 6, 
fig. 27. The nuclei are driven to the regions beneath the oil mass. 
Nevertheless at the next division the cells divide typically irre- 
spective of the distribution of the centrifuged materials. The 
result means that despite the forced position of the nuclei the 
spindle develops in its normal position, and gets its chromatin 
from the nucleus in the same way as does the segmentation 
spindle. 
If the egg is revolved in the four-cell stage, again the individual 
cells are centrifuged, plate 2, fig. V, and the same holds for the 8 
and 16-cell stages. Later stages than these I have not tested. 
