628 
T. H. MORGAN 
of the nucleus changes its staming character and becomes incor- 
porated in the general cytoplasm. Its extensive net- work and 
fluid are set free, and the rather small chromosomes collect in a 
mass near the spindle. One realizes how small a part of the germi- 
nal vesicle goes onto the spindle, and how large a part is con- 
tributed to the cytoplasm. Centrifuging the egg during the period 
of dissolution fails to move the chromosomes away from the 
spindle. In some eggs clear lumps appear in the cytoplasm, 
derived from the nuclear sap but it seems likely that these eggs 
were immature, for, these clear regions do not appear in the best 
sets. 
The polar spindle lies at first deep in the egg. If at this time 
the egg is centrifuged very hard the cytoplasm may be drawn out 
to produce the bottle-shaped figures (plate 7, figs. 36, 37, 44) 
mentioned above, or even, string-like processes. The latter 
representing the yolk-free parts are often broken off from the 
yolk mass figs. 41^3. The polar spindle may come to lie in the 
'^neck,'^ fig. 37 or even in the isolated fragment, fig. 38. Despite 
the great changes in the cell body, the spindle and the asters at 
its poles retain their characteristic shape. The rigidity of the 
fibres is admirably demonstrated under these conditions. The 
fibres are rarely displaced, or bent, or broken despite the exten- 
sive movements that must take place in the surrounding plasma, 
yet sometimes they are lost. 
I hoped to be able to determine whether fragments of the egg 
containing the polar spindle set free polar bodies, but the prepara- 
tions do not furnish sufficient evidence on this point. 
Eggs centrifuged during the period of extrusion of the first 
and second polar-body have shown that the spindle and chromo- 
somes move as a whole, and cannot be separated, and are seldom 
moved except when replaced bodily by the yolk. On the other 
hand when the pronuclei are formed these are readily transported 
to the polar cap. In this regard the results are the same as in 
Cumingia. Preparations of eggs killed at this time show that the 
male aster (or asters) is also as a rule carried with the nucleus 
to the pole, and is found attached to its more centrall}^ lying side, 
plate 8, figs. 47, 48, 49, 52. Despite its enforced passage through 
