No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 489 
A nucleolar change now occurs which I have never seen 
paralleled, and to my knowledge no similar morphological change 
has ever been described. At the time when the homogeneous 
substance of the cell is commencing to differentiate into the 
secretion corpuscles, the nucleus begins to withdraw its branched 
processes and to decrease in size; while so doing it discharges 
its nucleoli into the cell body (Figs. 197-199). There can be no 
doubt of the genuineness of this process, since I have examined 
at least two hundred nuclei at this stage, which showed all 
intermediate stages between nuclei which had discharged only 
a few nucleoli and those which had discharged all except a 
single one of their nucleoli into the cell. The study of these 
nuclei gives the impression that successive contractions of the 
nucleus take place, whereby at first all the more peripheral nucle¬ 
oli, and later those which are more central in position, become 
successively extruded, for in the cell two or three more or less 
parallel rows of nucleoli may be found, or more properly speak¬ 
ing, concentric circles of nucleoli (Figs. 197 and 198). In some 
cases I have observed nucleoli which were halfway through 
the nuclear membrane, but by far the greater number of the 
nucleoli are found either within or without the nucleus, and 
this would prove that the contractions of the nucleus are sudden 
in their action. I think that it is the sudden contractions of 
the nucleus which alone cause the expulsion of the nucleoli, 
for as the nucleus diminishes in volume its chromatin network 
may be seen gradually to become closer and denser, and the 
pressure within the nucleus becoming greater than the pressure 
without it, the nucleoli, not being fixed in position, are forced 
out into the cell body where there is comparatively little pres¬ 
sure, since the secretion corpuscles are not densely grouped, 
but lie scattered through a thin and structureless fluid substance. 
The nucleoli, when they have arrived in the cell body, are 
not found in equal number at all points around the nucleus ; 
accordingly they are probably not discharged from all sides of 
the nucleolus in equal number, but only there where the nuclear 
membrane is thinnest (it is probably thinnest at those points 
whither the nuclear processes had withdrawn themselves). But 
though the nuclear membrane appears to be thinner at some 
