CYTOLOGICAL STUDIES OF CEXTRIFUGED EGGS (325 
to the retention of all the chromatin; whether they become fer- 
tilized and if so, whether they produce normal embr^'os; whether 
the polar centrosomes disappear if replaced by the sperm aster, 
and, if not, what their fate may be; are all questions of prime im- 
portance. 
There is no evidence that these eggs develop b^^parthenogenesis. 
This suggests that parthenogenesis may have nothing whatsoever 
to do with the number of chromosomes in the egg. Hence those 
theories that try to explain the extrusion of the chromatin as a 
process to prevent self-development may be discarded, as well as 
those that explain fertilization as the outcome of the addition of 
more chromatin to the egg. 
The failure of the egg to divide at the time when the chro- 
mosomes move to the poles of the polar spindle seems to be due 
to the smallness of these spindles at this time, and since delay 
does not increase their size, their size must be determined by 
conditions existing in the egg prior to extrusion of the polar 
bodies — conditions that are subsequently set aside by the intro- 
duction of the aster from the male. The small spindles of the polar 
bodies suffice, however, to bring about division of the egg when 
carried to the surface. This result supports the view that I have 
suggested as to the function of the spindle. 
In some of the centrifuged eggs that correspond to the con- 
trols with two pronuclei, I have found a triaster in the middle of 
the egg. The triaster concerns onh^ the polar spindle and is not 
due to the addition of the sperm aster as shown by the small 
number of chromosomes, (plate 8, fig. 57.) The most probable 
interpretation is that one pole of the imprisoned spindle has 
divided and the chromosomes — whether divided as yet or not is 
not clear — have moved in part into the new spindle. This divi- 
sion of one pole may correspond to the division of that pole of the 
polar spindle that remains in the egg after the first polar body has 
been formed. The interpretation suggests that there is a differ- 
ence between the poles of the polar spindle and that it is not fortui- 
tous which one turns outwards towards the surface. 
In some eggs, which, as to time, correspond to the segmentation 
stage I have found spindles like those shown in fig. 58. There is a 
