630 
T. H. MORGAN 
astral rays extend into the egg. In fig. 48 the two new centers for 
the second division have been formed and lie in a bay of the nu- 
cleus. They have been carried with the nucleus to the top of the 
egg. In this figure some of the fibres appear to be bent in such a 
way as to change their course by 90,° but owing to the confusion 
of fibres in this region there is a chance of a misinterpretation 
of the real state of affairs. 
The nature of the cytasters and spindle 
Concerning the nature of the forces at work that produce the 
aster these experiments give no definite information, but they 
throw^ a good deal of light on the nature of the aster when it is 
formed. The fibres of the new aster appear more rigid than those 
of the older aster for the former appear seldom bent when the pro- 
toplasm about them is moved. The bombardment of the aster 
by the yolk granules tells the same story; for, the yolk granules 
filter through the aster without affecting it. Those only are 
caught that are carried down the funnel-like lines of the converg- 
ing fibres. The older fibres appear more often bent either because 
they are more flexible, or because they extend further into the 
cytoplasm and are more affected. Perhaps both conditions are 
involved. On coming in contact with the wall of the cell the fibres 
may be bent, and a similar phenomenon is seen when the polar 
spindle passes to the surface of the egg. In the latter case, how- 
ever, the bending might be supposed to be due to an active move- 
ment of the fibres, while such an interpretation seems excluded in 
the centrifuged eggs. 
The results show that the asters may be carried bodily through 
the cytoplasm without distortion. This fact creates at least a 
presumption in favor of the view that in the normal egg the move- 
ment of the aster or karyokinetic figure is due to a passive trans- 
portation through the cytoplasm, and that the movement is not 
due to a continuous dissolution or reformation of the aster in the 
direction of its movement. This conclusion has a bearing also 
^on the nature and formation of the astral S3^stem. 
