Davis . — N He tear Studies on Pellia. 173 
condition is nowhere permanent, but constantly returns to the 
granular state. The fibres then break down or are gathered 
up into some region of the cytoplasm which may have form, 
as at the cell-plate, but more frequently is a vague area near 
the nucleus. 
It is interesting to consider the bearing of these studies 
on theories of the physiology of mitotic phenomena. The 
facts seem to support the view of fibrillar growth and con- 
tractility. The spindle-fibres certainly enter the nuclear cavity, 
and the nuclear plate takes its form in consequence. Groups 
of fibres are plainly attached to the daughter-chromosomes, 
and probably contract, but it is not easy to demonstrate this 
point. However, the formation of the cell-plate gives strong 
evidence of contraction, as the spindle shortens and the fibres, 
drawing away from the poles, contribute their substance to 
the protoplasmic membrane that foreshadows the cell-wall. 
While growth and contractility are characteristic activities 
of the fibrillae, one must be impressed with the lack of 
evidence that these functions in Pellia are in any way con- 
trolled by morphological centres. Indeed it is even hard to 
believe in dynamic centres, so variable is the form of the 
kinoplasm. Yet dynamic centres may of course be conceived 
whose areas are comparatively ill-defined, and such may be 
presented by the centrospheres and by the vaguer kinoplasmic 
caps. 
But these are mere conjectures, and it is best to face the 
fact that we have little else upon which to construct our idea 
of the physiology of the achromatic portion of the nuclear 
figure than the conception of kinoplasm with its power of 
forming contractile fibrillae. 
Summary. 
At the time of sporogenesis the nucleus comes jto occupy 
the geometrical centre of the four-lobed spore-mother-cell, 
and there passes through synapsis previous to the first mitosis. 
Emerging from synapsis the nucleus presents a delicate 
