206 W. WALDEYER. 
The inner zone surrounds the nucleus, i.e. the daughter- 
nucleus, without a sharp outline. The constriction begins 
usually on one side, and, corresponding to it, a more highly 
refractive substance is perceptible, which persists during the 
subsequent separation, and stains more deeply with heematoxylin 
(see fig. 12). The process of division of the cell-substance must, 
as Rabl remarks, go on comparatively rapidly, since it com- 
mences with the daughter-skein stage, and is already finished 
before the resting stage of the daughter-nucleus is reached. 
I have already pointed out, in describing the spindle figure, 
that in plant-cells separate knot-like thickenings occur on the 
threads at the equator. Moreover, the number of spindle- 
threads increases, and as the thickenings become crowded 
together, and extend outwards to the surface of the cell, there 
arises what Strasburger calls a “ cell-plate,”’ which later repre- 
sents the “partition wall” between the two daughter-cells. 
Since, as already stated, such a wall is absent in animal cells, 
we do not find any formation of a cell-plate, or, at the most, 
only a trace of it, of which an account has already been given. 
Herein, therefore, is a difference between the issue of the pro- 
cess of cell-division in animals and plants. I repeat here, as 
said on p. 201, that, according to Carnoy’s observation, during 
the formation of the directive corpuscles of Ascaris megalo- 
cephala a distinct cell-plate makes its appearance in the 
position of the above-described thickenings. In preparations 
which van Gehuchten showed me I was able to satisfy myself 
on this point. 
Attempts to approach the striking phenomenon of karyo- 
kinesis from the theoretical side are, of course, not wanting. 
Excluding the writings of Biitschli (43), Fol (67), and Mark 
(181), who deal, on a broad basis, with the problem of 
cell-division and the physical forces to be taken into account 
the works of Roux (174), Pfitzner (153, 154), Carnoy (47), 
and Platner (161) must be mentioned. It can hardly be 
maintained that the theories suggested are good ones. It 
is always dangerous to theorise when the facts themselves are 
insufficient. Recent publications have shown that much is 
