CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 635 
it is that the development of the oil-pole may be responsible 
for the movement of some of the spindles into the interior. In 
fact Lillie thinks that the oil-pole may cause such a shift, but he 
implies that in such cases the spindle still keeps its radial posi- 
tion. There is another way, free from this objection that has not, 
it appears, been used to settle this question. If centrifuging is 
delayed until the first polar body is formed, that body should be 
found as often in the yolk hemisphere as in the light hemisphere, 
unless, in fact, the presence of this body acts as a load to turn the 
egg, as seems to occur to some extent in Cumingia, but the egg of 
Cerebratulus is so large that it may not be affected by the polar 
body. Different eggs should give different results in this regard. 
If the eggs are revolved either before the polar spindle form.s or 
when it is still present, those polar spindles that come to lie in the 
interior must penetrate the yolk sphere once more in order to 
reach the surface. Should the yolk-sphere be too dense to permit 
this we have the anomalous condition found in both Cerebratulus 
and Chaetopterus. 
What will happen to the delocalized spindle? If it fails to reach 
the surface again half the eggs should fail to extrude their polar 
bodies. Lillie does not state specifically that he has observed this 
in Chaetopterus, but his statement, that centrally lying spindles 
are found later, implies that polar bodies had not at that tin e 
been given off. The fate of these spindles and the history of such 
eggs is not described. I have already considered these questions 
for Cerebratulus and need not repeat here what I have there said. 
Lillie's conclusion in regard to the movement of the spindle in 
Chaetopterus has certain consequences that he has overlooked or 
else refrained from discussing. If, as he has tried to show, the 
centrosome is a ^'center of force" that produces the astral rays 
then when the centrifuge moves the kar3'okinetic figure as a whole 
through the egg the rays must form and reform at each step in its 
progress. When one considers all the consequences of such an 
assumption he will admit, I think, that such an interpretation is 
highl}^ improbable. 
The evidence on which Lillie bases his argument that the cen- 
trosomes are centers of force also rests, I believe, on a very un- 
