OF CELLS AND CELL-LIFE. 



125 



104. The multiplication of cells by duplicative subdivision, which is the most 

 common form of cytogenesis in the Vegetable kingdom, and which is particular- 

 ly well seen in the simplest Cellular Plants 

 (Fig. 5), is observed to take place also 

 within the Animal body, after a manner 

 essentially the same, in most cases in which 

 new parts are being developed in continuity 

 with the old. The most characteristic ex- 

 ample of it is seen in the early Embryo ; 

 which, at first consisting of but a single 

 cell, has its number of cells augmented by 

 such duplication, to 2, 4, 8, 16, 32, 64, &c. 

 (Fig. 6.) The same process may also be 

 watched through the whole of life in Carti- 

 lage ; and it is one of the means by which 

 the Red Corpuscles of the blood are multi- 

 plied in an early stage of their development 

 ( 149). The commencement of this pro- 

 cess in the Vegetable cell is indicated by 

 its elongation, and by a slight hour-glass 

 constriction (Fig. 5, 6), which seems due 

 to the tendency of the contents of the cell 

 to separate into two halves ; and between 

 these a division is subsequently formed 

 (GJ d) by the gradual infolding of the 

 " primordial utricle," or inner cell-wall, which is the true representative of the 

 wall of the Animal cell. 1 Where a distinct nucleus exists, however as is the 



Fig. 6. 



Hcematococcus binalis, in various stages of de- 

 velopment; a, a, simple rounded cells; 6, elon- 

 gated cell, the endochrome preparing to divide ; 



c, c, cells in which the division has taken place; 



d, large parent cell, in which the process has been 

 repeated a second time, so as to form a cluster 

 of four secondary cells, such as is often seen in 

 Cartilage. 



Multiplication of cells by binary subdivision; A, B, c, D, early stages of the process, from ovum of Ascaris 

 dentata; E, p, G, H, more advanced stages, from ovum of Cucullanus degans, 



case in most Animal cells the process of subdivision seems frequently to com- 

 mence in it ; for before any distinct inflection of the cell-wall can be perceived, 

 the nucleus may be seen to elongate, and to show a tendency to subdivision into 

 two equal parts. Each of these, wKen completely separated, draws round it a 

 portion of the contents of the cell ; so that the cell-wall, which at first exhibits 



1 See "Prin. of Phys., Gen. and Comp.," pp. 91, 92, Am. Ed. 



