7 
In every preparation that Ï made, the above observa- 
tions were confirmed dozens of times, so that [| amin no 
doubt that the nucleolus in Zygnema differs in type from 
that of the higher plants, and resembles the nucleolus of 
Spirogyra in having a peculiar structure. In Spirogyra 
there are two convoluted threads or a threadwork or 
network, in Zygnema cruciatum there are two short 
corpuscles united by a thread or indeed a thread with 
two thickened ends. 
Ï consider the main mass of the nucleolus in Zygnema 
as identical with the substance which occurs in Spirogyra 
together with the threads or the thread- or network in 
the nucleolus. I have not been able to answer the question 
whether the nucleolus in Zygnema, like that of Spirogyra, 
possesses a membrane. 
À few nucleoli did not seem to correspond to the above 
description, although I cannot definitely state, that these 
were aberrant. ÏI have never met with very abnormal 
nucleoli such as Escoyez observed in the resting nucleus 
so that the question occurs to me whether such nucleoli do 
not arise in fixing, like the perinucleolar cavity or whether 
perhaps they may be of a pathological nature. 
Karyokinesis. Ininvestigating karyokinesis in Zygnema 
the first question concerned the behaviour of the thread 
with tickened ends in the nucleolus, for in Spirogyra 
crassa | was able to determine without interruption the 
karyokinetic changes in the two nucleolar threads. In 
Zygnema I have not succeeded in doing this. Observa- 
tion in this case must necessarily be so much more minute 
and is accompanied by so many more difliculties, that 
after a few futile attempts I was obliged to abandon the 
study of the changes in the nucleolar thread. [I am unable 
therefore to give any further information about this impor- 
tant point. 
At the beginning of karyokinesis the nuclear network 
