1887] The Significance of Sex. 153 
Thus we get a notion of the cell as a most varied organism. 
Cells may be as varied among themselves as the higher organ- 
isms. But we have hardly begun to get an idea of the variety of 
karyokinetic phenomena; what is to appear by future study we 
can only vaguely imagine. The phenomena of cell-division can- 
not be purely physical phenomena. They are living phenomena, 
and show they are subject to the laws of heredity and evolu- 
tion of adaptation and variation. If this be so, we can under- 
stand karyokinesis only through comparative studies, just as we 
study the laws of variation and evolution, of homology and affin- 
ity with higher organisms. It becomes important, therefore, to 
understand karyokinetic phenomena among the Protozoa. Re- 
cent studies in this line have shown that here we may get nearly 
as complex figures of karyokinesis as in tissue-cells; but from 
this we get all grades down to the simplest direct division. We 
learn that nuclei may be alike in distantly-related forms, while 
closely-allied forms may have very diverse nucléi. 
2. Protozoa.—These organisms present, as we should expect, 
a great variety of nuclear forms and karyokinesis. The differ- 
entiation has been in so many different directions, with the ac- 
quirement of secondary characters whose physiological signifi- 
cance we can hardly guess, that it is perhaps impossible to 
connect the forms. Frey thinks the vesicular form of nucleus is 
the primitive one, but most writers agree with R. Hertwig in de- 
riving this form from a solid form through vacuolation of the 
latter, which leaves the chromatin either all in a cortical zone, 
or else in one or more nucleoli; and this process may be repeated 
in a nucleolus when this becomes large and important. Gruber 
suggests that in a primitive state the chromatin was present 
throughout the cell ina granular form, as in Trichospherium, 
Pleurophrys, Trachelocercus, Chcenia, and others, and that solid 
nuclei arose by fusion of these granules, or by some of them re- 
maining in close union following their multiplication. But it 
must be observed that this granular condition could easily arise 
by the segmentation of larger bodies and so be secondary in 
plasmic streaming in one direction. Each meridian bears a karyosoma that splits, 
because the fibre splits; thus, always in a meridional plane. The parachromatic 
mitom is so wound that the current is towards opposite poles in neighboring fibres 
after the splitting, hence the daughter PPE are swept to their proper poles. 
This theory appears to be as weak as its predecesso: 
