No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 467 



nodules of its meshes) stains a lilac-blue color. And since 

 it is wholly improbable that it should be derived from the 

 chromatin we must conclude that it takes its origin from 

 the nucleolus. In other words, a substance emanates from the 

 nucleolus and dissolves in the nuclear sap, and this process 

 must be regarded as the commencement of the dissolution of 

 the nucleolus. In support of this conclusion is the fact that 

 in many germinal vesicles the nuclear sap stains most intensely 

 in the neighborhood of the nucleolus (Fig. 309). Further, the 

 minute red-staining globules which later occur in the nuclear 

 sap must also be nucleolar in point of formation, i.e., be either 

 a substance given off in globular form from the nucleolus, or 

 be accumulations (perhaps chemically changed by the action of 

 the nuclear sap) of that nucleolar substance which has already 

 diffused through the nucleus. Of importance in this connec- 

 tion is the fact that these globules are often found in contact 

 with the nucleolus (Figs. 306 and 316). In all preceding stages 

 the nucleolus is regularly oval or spherical in outline, but in 

 the largest germinal vesicles not only may the size of its con- 

 tained vacuole be increased to such an extent that the original 

 ground substance forms only a thin shell around it (Figs. 308, 

 312, 314), but also its outline becomes frequently irregular 

 (Fig. 313); and in one case I found it broken at one pole, so 

 that its large vacuole communicated with the cavity of the 

 nucleus (Fig. 315). A morphological change in the shape of 

 the nucleolus which seems to take place with great regularity 

 consists in the indentation of the nucleolar wall at that point 

 where it is thinnest (Figs. 308, 314, 316). It would seem that 

 the pressure from without, i.e., the pressure of the nuclear sap, 

 being greater than the pressure of the fluid within the vacuole, 

 would cause the nucleolar wall to be pressed in at that point 

 where it is thinnest. The fact remains that the nucleolus 

 persists in the nucleus until a very short time before the pro- 

 duction of the pole spindle, and when the latter is formed no 

 trace of it can longer be found in any part of the nucleus or 

 cell. And since there is no reason for supposing that it is 

 extruded from the cell we must assume that it dissolves 

 within it. The red-stained substance and small jrlobules 



