the Development of the Organic Cell. 3 



new cells, but is only a phenomenon passively accompanying 

 cell-multiplication. 



The so-called nucleus is a nuclear cell possessing the faculty 

 of development, though frequently suppressed in the course of 

 development, and near to or within which two or more new cells 

 (cell-nuclei) may arise in order to carry on the multiplication of 

 the individual cell in question. Mirbel taught, and Mohl co- 

 incided with his views, that the fission of the cell proceeded by 

 the growth of centripetal septa, or of involutions of its wall, 

 breaking up its contents into sections, the external surface of 

 which became subsequently hardened into a firm lamina or spe- 

 cial cell- wall ; and side by side with, but partially opposed to, 

 this theory of cell-formation based on imperfect observations 

 Schleiden afterwards enunciated his peculiar views on the 

 function of the '^resting" nuclear cell — the cell-nucleus first 

 observed by Robert Brown, which, in cells developing slowly, 

 may be frequently met with. 



These opinions of Schleiden regarding the signification of the 

 nuclear cell became a great impediment to advancing the know- 

 ledge of cell-development. His followers entered so fully into 

 the notion that the nuclear sac is the constant formative centre 

 of the cell, exercising a catalytic efi"ect upon its fluid contents, 

 whereby it brings about the precipitation from the surrounding 

 fluid of a pellicular deposit around itself, that even those who 

 regard the whole organism as built up by repeated multiplication 

 of the first ovum-cell, resulting, as Mirbel supposed, from centri- 

 petal involutions of the integument, consider this cell-nucleus 

 as the starting-point in this mode of cell-multiplication. 



This involution is assumed to proceed, in these nuclear cells, 

 in the same way as in the parent cell-membrane itself, by con- 

 striction followed by division — each of the segments of the cell- 

 nucleus deriving, by means of a folding and constriction of the 

 inner lamina of its mother cell, a capacious envelope constituting 

 the wall of a new cell. 



This process of nmltiplication of the nuclear cell (cell-nucleus), 

 however, no more takes place than that of the mother cell by 

 constriction. 



The so-called constrictions or segmentations of the cell-nucleus 

 belong, in fact, to the same category as the so-termed germi- 

 nating cells. These forms are produced by the excessive develop- 

 ment of daughter cells in a feebly vegetating parent cell which 

 is in course of destruction ; whilst the partial septa or folds in- 

 terposed between the endogenous cells are not so much centri- 

 petal growths as the result of a passive condition of the cell-wall 

 at those parts. (The simultaneous growth of these septa with 

 the endogenous cells is not indeed a matter of direct observa- 



1* 



