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errors; and it clearly results from their mode of formation 
that they are no more Nematoids than are the whales—fishes. 
We have now to set forth the modifications which the 
pseudo-filaria undergo during their transformation into Gre- 
garine. 
The pseudo-filaria, simple threads of protoplasm, attenuated 
at one extremity, slightly swollen at the other or cephalic 
extremity, which is always richly charged with refringent 
granules, move about freely in the intestine during a certain 
time. Then the movements languish, and the length of the 
body diminishes little by little at the same time as the breadth, 
especially in the anterior portion (figs. 13 to 18). Soon all 
undulatory movement ceases, and the pseudo-filarium be- 
comes quiescent. ‘This is at least the conclusion derivable 
from the comparative examination of individuals, which are 
found in great numbers in the intestine. Some are seen 
which are very long, very thin, and extremely agile, side by 
side with others which are rigid, shorter, and obviously 
broader, especially in the anterior part of the body. At the 
same time there is seen to appear, near the middle of the 
long axis of the body, a dark circular spot, which is formed 
of a more refringent matter than the protoplasm (figs. 15 
to 17). The dimensions of this spot vary very slightly, but 
its limits become more distinct. ‘This is the nucleolus which 
appears directly in the protoplasm, probably as the result of 
a deposit, around an ideal point, of certain peculiar chemical 
elements, previously diffused in the protoplasmic mass. 
I can only explain this formation to myself by comparing 
it, as Schwann has done, in describing the free formation of 
cells in a blastema to a crystallisation. In the same way 
as given chemical elements in solution in a liquid can dispose 
themselves around a fictive point, so as to form a crystal, 
so here the elements of the nucleolus, diffused at first in the 
protoplasm, aggregate to form a globular body, a veritable 
nucleolus. 
The cell taken in its entirety appears to be an organic 
combination, comparable to those mineral combinations 
formed by crystals imbedded one in another. 
The nucleolar layer is of a different chemical nature from 
that of the nuclear layer, just as this also itself differs from 
the cell-substance. ‘This nucleolus is formed of a substance 
which differs from the primitive protoplasm by its physical 
and chemical properties, and these elements of the nucleolus 
have evidently a special function (as yet unknown) to perform 
in the life of the cell. 
These elements, primitively scattered in the protoplasm, 
