1887] The Significance of Sex. "149 
ter, like Van Beneden, into sap and nuclear substance, Strasdurger 
now proposes the following scheme. There are in the nucleus 
three formed substances, one of which is active. By the excita- 
tion of the cytoplasm the active substance gathers at the poles 
of the nucleus, leaving the spindle-fibres stretching between; the 
latter are cytoplasmic in origin, and the polar substance acts on 
them just as it acts on the fibres of the cytoplasm which form 
the stars, hence the general disposition of the polarized mole- 
cules in rows radiating away from the polar area. The third 
substance is first repelled from the poles to form the nuclear 
equatorial plate; but in some way there is a change of polarity 
by which it is subsequently attracted to the poles, and so the 
plate splits in two (it might also do this through internal repul- 
sion, but, as we shall show farther on, there is no necessity for a 
physical explanation). This is perhaps the best of the few theo- 
ries which have been advanced to account for the phenomena." 
On the question of the solution of the nucleus, Fo now took 
a middle ground, holding with Strasburger that the cytoplasm 
entering formed the spindle, but the nuclear matter simply be- 
came continuous ae the cytoplasm through the dissolution of 
the nuclear membran 
In 1878, Schleicher adtaindsd the view that the protoplasm was 
composed not of parts that had a fixed relation to one another, 
but of units that were independently mobile, and so all the struc- 
_ tures were amoeboid in form, hence there could be no definite 
phases during cell-division, wherefore he proposed the term 
karyokinesis to designate the phenomena. On the other hand, 
Flemming had, by careful staining, worked out the series of forms 
through which the nuclear matter passes during karyokinesis. 
He did not get the spindle well because, as he showed the next 
year, this was composed of non-stainable matter. The resting 
nucleus consists of a vesicle enclosing a reticulum and one or 
more nucleoli. This reticulum is changed to an exceedingly 
long and intricately wound filament, at the same time the nu- 
cleoli dissolve in the sap and the filament absorbs the material. 
This is the phase of the close knauel. (Fig. 112, a.) The filament 
now shortens and grows thicker, passing through the open 
* We give the theory in its most developed form, third edition of Strasburger’s 
work, 1880, where he slightly modified it from its original statement in the second 
edition. 
