KARYOKINESIS AND ITS RELATION TO FERTILIZATION. 161 
normal and pathological conditions, it is now known that 
cell-division, in opposition to the doctrine of spontan- 
eous generation of cells, holds the field, so that at the 
present day R. Virchow’s phrase, “Omnis cellula a 
celluld,” which concerns the chief facts in question, has 
universal acceptance. But, how does cell-division take place ? 
The scheme of division sketched out by Remak assumes that 
the process commences with the nucleolus and extends thence 
to the nucleus and finally to the cell-substance. The nucleo- 
lus divides into two parts, then the nucleus, and finally the 
cell-body. The process was apparently a very simple one. At 
the same time it was obvious that we had no true knowledge 
of the nature of this important process, nor of the powers 
which are operating, nor of the causes which lead the cell 
to divide. It was perfectly certain that the study of the 
process in question was very primitive, and that further 
research was necessary. 
It must be reckoned a distinct advance that the process of 
direct division of unicellular animals (A mcebze) and colourless 
blood-corpuscles (leucocytes) was followed under the micro- 
scope from beginning to end by Stricker (195), Klein (102), 
and especially by F. E. Schultze (184), and Ranvier (166). 
According to Schultze’s description for Amceba polypodia 
the nucleus first elongates, then becomes dumb-bell shaped, 
then the bridge between the knobs of the dumb-bell becomes 
thinner, then breaks across, and two nuclei are seen in the animal. 
At the same time a similar change is taking place in the clear ~ 
area around the nucleolus. The whole process of division of 
the nucleus and nucleolus is to be regarded as a single act, 
which lasts about a minute and a half. Then the body of 
the cell commences to elongate in the same direction as the 
nucleus and nucleolus previously did, and then in the same 
way there follow constriction, band-like stretching of the 
connecting bridge, and finally its rupture. Nothing was 
observed of any peculiar appearances, except that emphasis is 
laid on the fact that no pseudopodia are present on the bridge 
between the cell-bodies; whereas they project in opposite 
