CYTOLOGICAL STUDIES OF CEXTRIFUGED EGGS 
631 
If the asters are supposed to be the outcome of forces emanating 
from the centrosome or centrosphaere and if the maintenance of 
these fibres is due to the same activit}^ it is difficuh to understand 
how the fibres could become bent and maintain themselves for a 
time in this form. The preparations give every indication that the 
fibres are real although temporary structures. The observations 
give little evidence that could be used to interpret the rays as 
lines of force. 
The role of the astral system in cell-dirision 
If the astral rays are relatively rigid and if the sj^stem is moved 
passively through the egg, and does not move by its own activity, 
the process of cell-division can not well be attributed to the activ- 
ity in a dynamic sense of the fibre system. The change in position 
of the asters must, therefore, be the result of general movements 
in the cytoplasm that carry the asters with them. 
It is notorious nevertheless that the asters, or the poles of the 
spindle, when they come sufficiently near to the surface of the 
egg act in some way as centers around which the division takes 
place. It has been shown by Teichmann and by Wilson that as- 
ters representing the poles of neighboring spindles may also incite 
a plane of cytoplasmic division to pass through them. Evidently 
it is not necessary that a spindle containing dividing chromosomes 
shall be in the middle between two centers. This fact in itself 
makes improbable the view that the chromatin or chromosomes 
take any active part in division,- and consequently those theories, 
such as the recent one of Loeb, that rest on the assumption of 
some special activity emanating from the nucleus are probabh' 
incorrect. The same conclusion is made probable from those 
cases where the division plane falls entirely to one side of the 
chromatin so that one cell gets all the chromatin and one aster; the 
other cell gets only the other aster. Such a process cannot be 
interpreted on the basis of the nuclei as the focal points necessary 
for division. 
- Except in so far as the development of the central spindle brings about a 
sufficient separation of the poles to induce segmentation between them. 
