494 ARTHUR BOLLES LEE. 
plete. Where the plate is incomplete, the cytoplasm divides 
by constriction, and the nucleus may divide by cleavage of the 
spindle-plate. But it does not necessarily so divide. Both 
incomplete plates and complete plates may be formed and not 
utilised, the actual division taking place by constriction, and 
the plates disappearing either during the progress of the con- 
striction or before it has begun to be formed, or after it is 
completed (fig. 20). 
Conclusions.—The work I have thus shortly analysed esta- 
blishes some very important conclusions. Let me state them ; 
premising that if they do not appear convincing, that is 
because the limits of my space have obliged me to suppress an 
important part of the details of the observations on which they 
are founded. 
The phenomena of karyokinesis are highly variable and 
highly inconstant. None of them are essential. There is not 
a “phase,” from the formation of the chromatic skein or 
‘convolution ” to the reconstitution of the chromatic filament 
in the daughter-nuclei, that may not be omitted with impunity. 
Starting from the most complex phenomena of total karyoki- 
netic cell division, with their complicated and regular figures 
of the prophases, their multiplied fissions of the chromatic 
element, their orderly metakinesis, their orderly and compli- 
cated methods of reconstitution of the daughter-nuclei, their 
highly-developed spindles, spindle-plates, and cytoplasmic 
plates, we can descend gradually through forms of karyokinesis 
of increasing simplicity till we arrive at forms so degraded as 
scarcely to be distinguishable from processes of direct cell 
division. And when on the other hand we remember that 
modes of direct cell division have been described which possess 
some of the characteristics of indirect cell division, such as an 
imperfect spindle, a suggestion of a skein form of the chro- 
matic filament, or well-developed cell-plates, we are forced to 
conclude that direct and indirect cell division are not two 
essentially distinct processes, but rather modifications of one 
and the same general process. 
Secondly, this process is essentially identical in the animal 
