CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 609 
able, indeed, to move out of its path either the yolk or the oil if 
they stand in the way of its assumption of its proper position. 
If we knew the relative weight of the different materials of the 
egg and the rate of centrifuging that just permits their removal 
by the spindle, we might I should think calculate the forces that 
bring the spindle into position. 
The behavior of the chromatin at the time of its transfer from 
the nucleus in forced position to the spindle, calls for special treat- 
ment. In many of the nuclei the chromosomes appear bunched 
together in masses of varying size (figs. 17-20). These masses 
may pass in this condition on to the spindle. Their subsequent his- 
tory is difficult to make out. It appears that in most cases the 
chromosomes separate as they pass into the equator of the spindle. 
Presumably they then divide, but whether sister chromosomes 
always pass to opposite poles, or whether they may sometimes 
be unequally distributed I do not know. 
The question arises as to what causes the heaping up of the 
chromosomes. There is no evidence that it is caused b}^ the cen- 
trifuge and the evidence is very strongly in favor of the view 
that the chromatin in some way draws towards the aster pole. 
The most probable interpretation is, I think, that these nuclei lose 
their orientation to the aster at a critical time and are unable to 
regain it before the chromatin is resolved into its chromosomes. 
The irregular position of the chromosomes with reference to the 
aster is the cause of their heaping together which is avoided in the 
normal egg by the pole of the nucleus being oriented to the aster 
which permits the ends or angles of the chromosomes to pass 
directly without interference to the spindle. 
Whatever be the cause of the heaping of the chromosomes, one 
important fact emerges, viz. : the chromatin material is moved 
or is drawn as a mass to the aster that is nearest to it. The bear- 
ing of this evidence on the interpretation of movement in the 
chromosomes will be discussed later. 
In eggs that have been kept on the centrifuge from the time of 
formation of the pronuclei until the first cleavage is completed, I 
have noticed that the nuclei in the blastomeres are often ex- 
tremely small (plate 6, fig. 28 and plate 2, fig. U) . Compared with 
