476 SUMMARY OF CURRENT RESEARCHES RELATING TO 



denser substance of which a ni;mber of densely packed granules are 

 frequently imbedded. These granules, which assume a deeper colour 

 uuder tincture, and which vary greatly in size, form, and number, 

 have been termed by Flemming " chromatin-granules " ; the larger 

 of these have been long known as nucleoli. These chromatin- 

 granules certainly sometimes multiply by division ; possibly, also, by 

 new formation. Whether they are essential constituents of the 

 nucleus, or only enclosures, is doubtful. The nucleus always multi- 

 plies by division, and, in all observed cases, by bipartition, although 

 the details vary greatly in different cases ; but the various modes 

 graduate into one another, and may be regarded as modifications of 

 one and the same process. 



In the simplest case, the mature nucleus simply undergoes trans- 

 verse division, without any striking change in its chromatin-bodies ; 

 only an inconsiderable change in its internal mass is indicated by the 

 longitudinal streaking of the matrix. In other cases, simultaneously 

 with the division of the entire nucleus, the chromatin-bodies also 

 divide, with changes in form more or less complicated. With this is 

 combined the additional phenomenon, that the mass of the old nuclei 

 is not identical with that of the two daughter-nuclei ; but that a con- 

 siderable portion of its matrix, usually displaying obvious longitu- 

 dinal fibrous structure, is eliminated, and incorporated with the 

 protoplasm-body of the cell, while the chromatin-bodies of the old 

 nucleus, divided into two groups, together with a portion of the 

 matrix, become differentiated into two daughter-nuclei. Finally, in 

 the most complicated case, the differentiation of the matrix of the 

 nucleus from the surrounding protoplasm is lost almost from the first, 

 and a fibrous differentiation, like that in the matrix of the nucleus, is 

 exhibited also in a larger or smaller portion of the surrounding proto- 

 plasm ; and finally, each of the two groups of chromatin-bodies of 

 the old nucleus, with a portion of this fibrous protoplasm, separates 

 into a daughter-nucleus, while the remainder of it, with the rest of 

 the surrounding protoplasm, forms the protoplasm-body of the new 

 cell. 



This last mode of division of the nucleus occurs in the meristem 

 of the Archegoniatse and Phanerogams, where a rapid increase of the 

 protoplasm is necessary for the great multiplication and increase in 

 size of the cells. The author believes that the matrix of the nucleus 

 is probably only a denser portion of the protoplasm-body itself, 

 adapted to special physiological functions. 



With reference to the relation of the nucleus to the entire cell, 

 the author states that the dissolution of the two usually coincides in 

 time ; it has already been shown that previous statements of a dis- 

 appearance of the nucleus in the living cell rested on erroneous 

 observations. Where the nucleus displays motility, this is, in all 

 observed cases, only passive ; there is never any active change of posi- 

 tion. The cell-nucleus must therefore be regarded as a differentiated 

 portion of the protoplasm-body of the cell, differing slightly in its 

 substance from the surrounding protoplasm, and containing in 

 its interior structures, varying in number and arrangement, but very 



