CELLS. 33 



contents with a nucleolus appear. Its development may in 

 this case be compared to that of inorganic precipitates, yet 

 the constantly globular figure, and the size of nuclei which 

 are just formed, indicate some essential though not yet re- 

 cognised condition peculiar to them. Secondly, cell-nuclei 

 are produced endogenously in nuclei, or by their division 

 under the influence of a nucleolus, which also divides. Here 

 is one condition which is never presented by crystals, — the 

 division from an internal cause ; while the other, the influence 

 of the nucleoli upon the nucleus, can hardly be comprehended 

 in any but a physical way, as a molecular attraction proceeding 

 from the nucleoli, of an indefinable nature, which at last draws 

 the entire half of the parent nucleus within its influence. 



2. In the development of cells by division, the cell-nucleus 

 plays exactly the same part which was previously ascribed to 

 the nucleolus, and the occurrence of the formation of cells in 

 this manner demonstrates that chemical conditions are not 

 necessarily concerned therein. 



3. In cell-development around portions of contents, and in 

 the cleavage process, the nuclei also operate as simple centres of 

 attraction (einfach attrahirend) upon a certain mass of blastema, 

 and then follows the formation of a membrane upon the surface 

 of this mass, which is most simply understood as a conden- 

 sation of the blastema. 



4. In cell-development directly around the nucleus, the 

 investment with blastema is wanting, and the nucleus deve- 

 lopes the membrane immediately around itself. This pro- 

 cess admits of both a physical and a chemical explanation. 

 In the first place, we may with Schwann assume that the 

 nucleus attracts molecules, which, when they have reached a 

 certain amount, condense into a membrane, and, by growing, 

 become detached from the nucleus. Or secondly, it is con- 

 ceivable, that the nucleus in some manner initiates chemical 

 processes, which terminate with the formation of a membrane 

 around it. In this way a coagulable substance might be pro- 

 duced within and excreted from it ; or, like rennet upon casein, 

 it might act upon the protein combinations in the cytoblastema, 

 in such a manner that they should coagulate where in contact 

 with it ; or lastly, by the extraction of the alkali it might 

 render an albuminous substance insoluble, as is the case in 



i. 3 



