KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 165 
the drawing the plan of the arrangement of the threads in 
a resting nucleus according to Rabl’s idea; on the left only 
the primary threads are drawn. The nucleus is represented 
in side view, the pole (P.) above, the antipole below. To the 
right, which represents the resting condition of a nucleus, two 
primary loops are to some extent recognisable, but passing 
from these are numerous secondary threads, uniting with one 
another and with the primary. threads, and in some places the 
thread substance has collected to form knot-like masses (net- 
knots). A rounder nucleolus is also shown. One can easily 
see that the primary threads must be so much the more diffi- 
cult to make out the more the substance of which they con- 
sists radiates into secondary threads and accumulates in 
knots. Thus it happens, according to Rabl, that in the resting 
nucleus the regular arrangement of thread-loops with pole 
and antipole seems to be obliterated, but it can be re-estab- 
lished in a moment if the fibrillar substance can in any way 
be made to return to the main course of the primary threads. 
Herein lies the importance of the regularity of the thread- 
work for karyokinesis. We shall return later to this point. 
The structure of the network is peculiar in certain cilio- 
flagellata, e.g. Ceratium tripos. Here Biitschli (44) finds 
a honeycomb structure with perfectly closed meshes, so that 
the nucleoplasm, although the nuclear membrane is absent, 
is not in direct communication with the protoplasm. In 
plant-cells no so-called secondary threads forming a net- 
work were found by Strasburger (191), nor was he able to 
make out with certainty whether during the resting stage only 
one thread was present or several threads; and if the latter, 
whether they have a definite arrangement. 
We must now mention certain peculiarities in the behaviour 
of the nucleus and its constituents to chemical reagents and 
stains, as well as the constituents present in addition to the 
network ; namely, the nucleoli, the nuclear membrane, and 
the nucleoplasm. 
Weak acids (acetic, formic, &c.) render the network and 
the nucleoli distinct ; water causes them to swell up; chromic 
