R. S. LILLIE. 



these attractive forces being to draw the chromatin toward the 

 center of the cell. On the other hand adjacent chromosomes or 

 adjacent portions of the chromatic filament are by their own 

 mutually repellent action exposed to an opposite influence which 

 resists their approach toward one another. Hence the position 

 of equilibrium, i. e., the stationary position which they finally 

 adopt, must be one where these two opposed sets of influences 

 exactly balance each other. 



The formation of the spireme and of the equatorial plate may 

 then be ascribed to these two chief conditions, one the attractive 

 influence that draws the chromatin toward a central position and 

 tends to keep it there, the other the mutually repellent action of 

 the chromatin particles themselves. The stationary position is 

 one of equilibrium between these two opposed tendencies. 



I should add here, in reference to the striking fact that the 

 chromosomes at the metaphase occupy positions side by side /;/ 

 a single plane - - that of the equator of the cell that this re- 

 markable peculiarity of disposition also remains to be accounted 

 for. As yet, however, I know of no experimental facts bearing 

 directly on this problem ; and in the following explanation of the 

 manner in which the equatorial plate is formed, I shall assume 

 from the first that the chromosomes are free to move only in this 

 single plane, without as yet attempting to explain why this is so. 



EXPERIMENTAL. 



It the conditions of spireme-formation and of equatorial plate- 

 formation are similar to those suggested above, it should be pos- 

 sible to simulate these phenomena experimentally by making 

 use of artificial filaments composed of mutually repellent units 

 arranged in rows, and by subjecting these to the action of some 

 centrally attracting force. The disposition and relative positions 

 assumed by such filaments should, if the above hypothesis is 

 correct, resemble those exhibited by the chromatic filament and 

 chromosomes in the dividing cell. 



In pursuance of this idea I have experimented with filaments 

 consisting of rows of floating magnetized needles. The experi- 

 ments of Alfred Mayer on floating magnets are well known to 

 physicists ; he studied many years ago the behavior of groups 



