
The Dual Force of the Diniding Cell. 549 
consideration of the character of the force operative in determining the 
cytoplasmic figure, which we term “mitokinetic force” (our reason for using 
this term rather than “ karyokinetic force” will be found below, p. 564). 
The behaviour and influence of the chromosomes we pass over for the 
present. | 
We must note that the figure as described is formed by growth; its origin 
in animals is in a minute granule, the “ centriole,” which becomes surrounded 
by a zone of clear cytoplasm, the “centroplasm”; this grows endogenously 
besides sending out from a peripheral “mantle-layer” rays into the ambient 
plasma, along which undoubtedly food-material passes. This centroplasm 
has within i no trace of radial structure, but consists of alveoli which enlarge 
as the structure grows (fig. 4). A second centroplasmic layer is formed 
within in contact with the centriole; and, as this grows, the alveolar layer of 
the original centroplasm becomes radially elongated, and affords a transition 
to a truly fibrillar radial structure; this is repeated a third time, whereupon 
the centriole divides with its inner centroplasm, and thus are formed the two 
“ centrospheres ” or “centrosomes” that constitute the ends of the dumb-bell 
of division. While the division of the centroplasm is taking place, the 
centroplasmic mass grows round the nucleus (in the oosperm the conjoined and 
appressed male and female nuclei); we may say that the nucleus becomes 
imbedded in the centroplasmic mass almost like an apple in a dumpling, so 
that the two centrospheres lie on either side of the nucleus. 
The nuclear wall disappears (first at the two sides turned to the respective 
centrospheres); and the spindle is formed or rather completed by the 
extension of the inner rays across the nuclear space, while the rest of the 
nuclear contents are resolved into the chromosomes. 
This is the history of the first seementation-figure of Rhynchelmis (figs. 3—5d), 
a worm allied to the common Blood-worm of our pond and ditch bottoms. I 
have selected it because the cytoplasmic figure is the largest known 
(1/125 x 1/100 = 0:20 x 0°25 mm.), and because it has been fully studied by 
Vejdowsky and Mrazek; while, thanks to the kindness of the former, [ have 
enjoyed the opportunity of studying some of the most important stages on 
the original specimens. In other cases, as in sperm-formation, a pair of 
minute centres united by a tiny spindle is seen on one side of the nucleus, 
and enlarges by the growth of all its elements except the centrioles: the 
spindle here seems to be bounded by a semi-pervious layer and to be 
turgescent as it grows. The figures (1, 2) copied from Wilson show a process 
of this type. | 
Again, in Higher Plants the poles have, as a rule, no visible existence 
except as indicated by the point to which the spindle-fibres converge at 
oP 2 
