66 EDWIN G. CONKLIN 
though much elongated preserve their usual appearance. In this 
regard my work confirms the conclusions of Morgan (’10) as to 
the nature of the spindle in Cerebratulus, and is at variance with 
the work of Lillie (09) on Chaetopterus. 
In fig. 12 an egg is shown which was centrifuged for fifteen 
minutes during the first cleavage and was then left for three 
hours in sea water. The axis of centrifuging is indicated here, 
as elsewhere, by the lighter vacuolated substance at one pole 
and the heavier yolk at the opposite pole; this axis is also marked 
by an arrow, the head of the arrow marking the distal pole during 
centrifuging, the tail of the arrow the central pole. In figs. 12 
to 15 the first cleavage plane does not pass through the animal 
pole, which is marked by the polar bodies, but is displaced to one 
side, and the cleavage is not meridional, as in normal eggs; 
furthermore the cleavage is not equal, quantitatively and qualita- 
tively, as in normal eggs, but is markedly unequal, most of the 
cytoplasm having gone into the smaller one of the two daughter 
cells, while the larger one contains little cytoplasm and much yolk. 
This is evidently due to the fact that the greater mass of yolk 
in the larger cell has displaced the cleavage plane to one side of 
its normal position. 
Corresponding to this difference in the quantity of cytoplasm 
in the first two blastomeres of these eggs, there is a decided dif- 
ference in the size of the nuclei and spheres, the latter always 
being proportional in size to the quantity of cytoplasm in which 
they lie. The smaller cells with the larger quantity of cytoplasm 
thus have larger nuclei and spheres than the larger cells, which 
have a smaller quantity of cytoplasm. 
The eggs represented in figs. 13, 14, and 15 were centrifuged for 
five hours during the first cleavage and were then fixed at once. 
It is evident that division took place while the eggs were on the 
centrifugal machine and that the daughter nuclei have grown to 
the size shown while the eggs were still being centrifuged. Other 
eges centrifuged for the same length of time were allowed to 
develop further after being removed from the centrifuge, and 
they show that in most cases the eggs were still alive after cen- 
trifuging and not seriously injured. Fig. 13 shows a very note- 
