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 whither the nuclear processes had withdrawn themselves).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 



