114 Darwin, and aftcr Darwin. 
(Fig. 29), we see the complex processes of karyokinesis 
in the first two stages of egg-cell division. But 
similar processes continue to repeat themselves in 
subsequent stages; and this, there is now good reason 
to believe, throughout a the stagcs of cell-division, 
whereby the original egg-cell eventually constructs an 
entire organism In other words, all the cells com- 
posing all the tissues of a multicellular-organism, at 
all stages of its development, are probably originated 
by these complex processes, which differ so much 
from the simple process of direct division in the 
unicellular organisms!. In this important respect, 
therefore, it does at first sight appear that we have a 
distinction between the Protozoa and the Metazoa of 
so pronounced a character, as fairly to raise the 
question whether cell-division is fundamentally identical 
in unicellular and in multicellular organisms. 
Lastly, the only other distinction of a physiologically 
significant kind between a single cell when it occurs 
as a Protozoén and when it does so as the unfertilized 
ovum of a Metazo6n is, that in the latter case the 
nucleus discharges from its own substance two minute 
protoplasmic masses (“ polar bodies”), which are then 
eliminated from the cell altogether. This process, 
which will be more fully described later on, appears 
to be of invariable occurrence in the case of all egg-cells, 
1 T say “probably,” because analogy points in this direction. As a 
matter of fact, in many cases of tissue-formation karyokinesis has not 
hitherto been detected. But even if in such cases it does not occur— 
i.e. if failure to detect its occurrence be not due merely to still remain- 
ing imperfections of our histological methods,—the large number of 
cases in which it has been seen to occur in the formation of sundry 
tissues are of themselves sufficient to indicate some important difference 
between cells derived from ova (metazoal), and cclls which have not 
been so derived (protozoal). Which is the point now under discussion. 
