CYTOLOGICAL STUDIES OF CENTRIFUGED EGGS 615 
cytasters, yet the formation of these bodies may also take place 
independently of the original centers. These views are not, 
I think, incompatible but rather supplementary. If we look 
upon the centrosome not in the light of a cell organ, but rather as 
a center about which the ray formation is more likely to develop 
than elsewhere, we can harmonize many kinds of evidence. 
When I think of the phenomenon as a process similar to crystalli- 
zation I get so much clearer a conception of it that I am tempted 
to describe it in this way. When, for example, the egg of the 
sea-urchin is put into concentrated sea water numerous stars 
are slowly formed. The center of each star would be formed 
wherever the concentration began to be a little denser than else- 
where. About these centers the crystal rays would develop. 
The centers might remain, in potentia, when at a later phase of 
the cell division the crystallizing forces had weakened, owing, 
let us say, to the absorption of water, for which there is some 
direct evidence. The center might again act as the central points 
in the formation of the next asters. 
From this point of view the spermatozoon brings into the egg 
a crystallization center about which the ray formation would 
take place more readily than elsewhere. The rays would repre- 
sent real, although temporary structures. Their formation would 
cause certain changes in the equilibrium of the cell that would 
lead finally to the division of the cell about each aster as a cen- 
ter. We might think of such systems developing in certain direc- 
tions more easily than in others; these directions corresponding to a 
stereometrical condition of the egg plasm. Cytologists have often 
discussed the question whether the rays represent lines of force in 
the sense that the aster is a dynamic center controlling the 
changes that take place about it. On the view here suggested the 
center is not a center of emanations or diffusion, for, it does not 
exert an action at a distance through the cell, but is a center about 
which a system is built up depending on the crystallization proper- 
ties of the molecules of the protoplasm. The rays are lines of force 
only in the sense that they represent the forces of crystallization. 
The rays are not lines of force in the sense that the center is exert- 
ing a radial influence on the cell or that the center itself is a dy- 
