722 THE AMERICAN NATURALIST. [VOL. XXXIX. 



(Davis, :oi, p. 171) are outlined the changes in form which 

 kinoplasm may assume in the mitoses of the liverworts upon 

 which is based a theory of a cycle through which kinoplasm 

 may run in the history of a cell. On this theory, centrosphere, 

 polar cap, and the free fibrillar condition are all secondary devel- 

 opments from a primal finely granular kinoplasm which is the 

 only form of kinoplasm that is in any sense permanent in the 

 cell. This finely granular kinoplasm is always present in char- 

 acteristic form in the plasma membranes of the cell. The sub- 

 stance of centrospheres, polar caps, and fibrillae arises from 

 accumulations of granular kinoplasm during prophase and these 

 structures return to the same undifferentiated granular kino- 

 plasm at the end of mitosis or become lost in the general 

 cytoplasm of the cell. 



The cycle is from an undifferentiated finely granular kino- 

 plasm through certain specialized conditions either wholly or 

 in part fibrillar in structure back to the granular state. The 

 centrosphere and polar cap are regions from which fibrillae de- 

 velop at least in part and to which they may remain attached as 

 to an anchorage. The polar cap is a less clearly differentiated 

 kinoplasmic center than the centrosphere but does not differ 

 from it in the essentials of its organization. It seems to me that 

 the two structures are very closely related in the liverworts and 

 that in this group we may readily conceive the polar cap as de- 

 rived from the centrosphere. The 'free fibrillar type of spindle 

 formation is a step farther in the direction of such a distribution 

 of the kinoplasm that no very positive centers for the develop- 

 ment of the spindles may be distinguished. The four-rayed 

 structure (quadripolar spindle) so characteristic of the spore 

 mother-cell in the Jungermanniales represents a group of four 

 temporary centers for the formation of fibrillae and there is 

 clearly a gathering of kinoplasm at these points but the regions 

 are so vague in outline as hardly to justify the designation of 

 centrospheres. From the fibrillar state, kinoplasm returns to 

 the finely granular condition by the contraction of the fibers 

 which thus contribute their substance to some common area. 

 The area may lie around the chromosomes of the daughter 

 nuclei where it becomes later in part at least a nuclear mem- 



