CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 607 
tions of the aster and nuclei before centrifuging with reference to 
the direction of centrifuging. I have not studied in detail the nor- 
mal fertilization in Cumingia, but there is every evidence that the 
egg follows the typical process of the group to which it belongs, 
viz., a centrosome and aster appear near the male nucleus, divide, 
and produce the segmentation spindle, plate 4, fig. 10, that 
collects the chromosome from both the male and female pronuclei. 
The spindle takes such a position in the egg that the first plane of 
cleavage passing through it also passes through the pole of the egg. 
If the egg has been centrifuged during the earlier pronuclear 
stages I often fail to discover the aster either because of dif- 
ficulty in locating it or because it is obscured to some extent 
by the centrifuging, or because the series of sections is imper- 
fect; but there is no doubt that it is present ; first, because a 
spindle appears in each egg at the same time as in the normal, and 
secondly, because in polyspermic eggs as many asters (or pairs of 
asters) appear as there are male pronuclei present. This latter 
point is a matter of no little importance. It shows that the cen- 
trosome and aster are actual things that exist independently of 
the nuclei that come with them into the egg; for, in this case the nu- 
clei have been carried away from the asters by the centrifuging and 
yet the asters continue to go through their regular phases. No 
new asters develop near the nuclei in their new position — at least 
I can find no evidence of such neo-formation — but in polyspermic 
eggs a cluster of asters appears beneath the nuclei, plate 5, fig. 15. 
The evidence is a virtual demonstration of the independence of the 
asters. 
In later pronuclear stages the asters are large and are nearly 
always found near the center of the egg beneath the pronuclei, 
plate 4, fig. 12; plate 5, figs. 16, 18, 23, 24. Fibers from the aster 
run to the pronuclei where they seem to be attached. This re- 
lation suggests that as the nuclei are carried toward the oil cap 
they often still remain anchored by one side to the old aster. If 
this is the correct interpretation the nuclei must revolve as they 
move. 
We come now to an important question — how do the spindle 
and chromatin in these eggs with displaced pronuclei get into 
