KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 171 
composition of cytoplasm, F. Schwarz recognises (1) *‘ plastin ”’ 
(Reinke) or “ cytoplastin,”’ a viscous, extensible mass, which 
resists pepsin and trypsin digestion; (2) ‘‘ microsomes”’ in- 
soluble in water and in cytoplasm. These are of different 
composition in different cases, and therefore cannot be com- 
pared with the chemically uniform chromatin bodies of the 
nucleus; (3) the substance dissolved in the vacuoles. The 
microsomes may be absent. Nos. | and 8 are always present. 
These are, of course, found chiefly in plant-cells. 
We will now return to the process of karyokinesis, and 
follow the description of it which Rabl (165) has most recently 
given, and which, as already stated, agrees in all essential 
points with that given by Flemming (58). 
We start with the resting nucleus, as represented in fig. 1, 
which also represents the first stage of karyokinesis in which 
all the secondary threads of the network, as also the nucleoli 
and net-knots have disappeared, their substance passing into 
that of the primary threads. Fig. 4 shows a nuclear scheme, 
in which, on the right side, net-knots and a nucleolus are 
distinct, whilst on the left they are absent. If we imagine the 
secondary threads, knots and nucleolus to become absorbed 
into the primary threads it will represent the first stage of 
karyokinesis, as is shown in fig. 2 as seen from the polar field. 
We call this stage, with Flemming, the “ Knatel-stadium ”’ 
(skein stage), or “ spirem,”! or “ mother-skein.” 
EK. van Beneden (23) was the first to show, for the egeg- 
cell, that the chromatic threads, with the distinct appearance 
of which karyokinesis commences, is only a portion of the 
network existing in the nucleus, and it is now distinct because 
of the denser aggregation of “chromatin.” Rabl has recog- 
nised this in other cells, and generalised thereon. 
Contemporaneously with this change an increase in size of 
the whole nucleus is perceptible. 
Balbiani and Strasburger have, as already said, stated their 
opinions, with which the descriptions given by Flemming and 
Carnoy agree, that in the resting nucleus and at the com- 
1 orepypa = a twist or ball of thread. 
