616 
T. H. MORGAN 
namic force. My interpretation is more in harmony with what we 
see, and is more in accord with the well known changes that take 
place as the asters form and reform in the egg at its different 
phases. A further consideration of this question may be deferred 
until the experiments with Cerebratulus have been described. 
I have given the evidence that seems to me to show that the 
chromosomes move or are drawn towards the asters to whose 
fibers they appear to become attached. It has long been debated 
whether the fibers draw the chrosomes to the center, as an elastic 
fiber might be supposed to act, or whether the chromatin glides 
along the fibers as paths. Concerning the mechanism of the proc- 
ess I have nothing new to offer, but I see no difficulty in bringing 
the movement into line with the suggestion offered above that 
the fibers of the asters are crystalline products of the cytoplasm, 
for however they act they represent lines in the cell that differ 
physically from the rest of the cytoplasm, and the chromosomes 
might react to such lines in a way different from the way in which 
they react to the rest of the cytoplasm. 
The movements of the aster in the egg. The migration of the asters 
through the cytoplasm towards certain well defined regions and 
the movements of the spindle as a whole are well known phe- 
nomena to every embryologist. The mechanism of these changes 
is entirely unknown, but we know that the movements follow 
certain axial relations of the egg. In cleavage it is known that the 
asters behave in a perfectly definite manner, that is connected with 
the cleavage pattern and, presumably, with some system in the 
egg. Their migration can be readily affected by pressure applied 
to the egg, and from this evidence, I have argued elsewhere, that it 
seems probable that the rays develop in accordance with the lines 
of tension in the egg. It has been generally taken for granted, I 
think, that the movement of the polar spindle to the animal pole 
of the egg is in some way connected with the presence in that part 
of the egg of materials that make it easier for the spindle to move 
to this point, or else, it has been assumed, that the spindle takes 
the shortest course to the surface irrespective of what point of 
the egg surface lies nearest to it. Both of these views are refuted 
by the evidence from the centrifuged egg. It has been shown that 
