CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 643 
their membranes readil}^ after the blastodisc has begun to form. 
It still remains to be shown whether the same orientation occurs 
before the blastodisc has begun to thicken. Owing to the differ- 
ence in thickness of the outer protoplasmic layer, it is possible to 
settle this question also by direct observation. If unfertilized 
eggs are put into a tube and rotated so slowly that no change in 
the protoplasmic layer is effected, and the tube containing the 
eggs be examined under the microscope (care being taken to keep 
it in the same position it held on the centrifuge) it will be found 
that the eggs orient within their membranes. 
2. If the eggs soon after removal are shaken about in sea- 
water it will be found that in many cases the thickest part of the 
protoplasm no longer coincides with the micropj^le. This shows 
how easily the egg shifts within its membranes. 
3. If, after centrifuging, the egg nucleus or the spindle were 
left behind in their normal positions when the rest of the proto- 
plasm was carried into the artificial blastodisc, we should expect 
to find after a time a certain accumulation of protoplasm around 
the nucleus, to judge from analogy with what occurs around the 
sperm nuclei, but none becomes apparent. For instance, eggs 
were centrifuged to various extents, and then left to stand for an 
hour or more without fertilization. No evidence of any accumu- 
lation of protoplasm, except in the region of the blastodisc, was 
found. 
From the foregoing evidence there can be no doubt, I think, 
that the eggs orient within their membranes under the influence 
of a strong centrifugal force, and that the egg membranes do not 
always turn when the egg turns, owing in all probability to the 
pressure of the eggs on each other. If floating freely in the water, 
however, the membrane and the egg usually turn at first together 
as I have seen. 
The effect of centrifuging the eggs immediately after removal 
from the fish 
When just out of the fish the surface of the egg is in intimate 
contact with the inner surface of the membrane, so that the egg 
