626 
T. H. MORGAN 
large barrel-shaped central spindle containing a large number of 
chromosomes and fibres, and two polar asters with few fibres 
resembling in every respect the asters of the polar bodies. The 
fibres that run from these to the central spindle are far less numer- 
ous than the fibres of the spindle and the poles appear quite 
reduced compared with the large poles of the segmentation nu- 
cleus. Provisionally, I interpret the result to mean that the chro- 
mosomes of the polar spindle have divided once or twice, but the 
polar centers have not divided. The chromosomes or the nucleus 
from which they are derived are responsible for the central 
spindle. The number of the fibres of this central spindle is deter- 
mined by the chromosomes or whatever goes along with them in 
the nucleus. Their number corresponds with that of the chromo- 
somes. The asters, however, are those belonging to the polar body ; 
the number of their rays now falls far short of those of the central 
spindle, hence the peculiar type of karyokinetic figure that is 
found. 
Should this interpretation be established it suggests that the 
fibres of the central spindle of the karyokinetic division arise 
from nuclear material, or possibly from the chromosomes them- 
selves or from the linin ; and that the rays from the centrosomes 
establish a secondary connection with these. I hope by further 
observations, more completely controlled, to test the validity 
of these inferences. 
Segmentation of -the centrifuged eggs 
Segmentation has been studied in eggs centrifuged at various 
stages prior to division. In general it ma}^ be said that the yolk 
sphere does not break up and redistribute the yolk granules prior 
to division except perhaps to a limited degree. The yolk mass 
appears to offer a serious obstacle to the passage of the cleavage 
furrow as shown in plate 6, fig. 35. The development of such eggs 
has not been studied in detail. In some cases where the yolk 
is not too compact the cell wall cuts through and equal cells 
result. From these the normal embryos that have been found in 
some cases probably develop. In many of the first segmentation 
