DEVELOPMENT AND MULTIPLICATION OF CELLS. 



Ill 



Fig. 14. 



particles (or diffused nucleus ?) of the cells, in the genus Zygnema, presenting 

 a regular spiral arrangement at one period of their growth (Fig. 13). And 

 in other instances, as in the cells of the petal of 

 the common Geranium (Pelargonium), we find 

 the nucleus sending out curious stellate or radi- 

 ating prolongations (Fig. 14.) These facts are 

 of much interest, as illustrating some of the more 

 obscure changes which are believed to take place 

 in animal tissues. 



125. But the nucleus may also be the source 

 from which the new cells arise, that are devel- 

 oped within the cavity of the parent. Several vari- 

 eties in the mode in which this process takes place, 

 are presented to our observation in the simplest of 

 the Cellular Plants, belonging to the group of the 

 Fresh-water Algae ; the growth of which may be 

 studied with peculiar facility. In some of these 

 the cell is destitute of a nucleus, but is filled with 



a very finely-divided granular matter, the en- Cells from the petal 



. J > ,, ,, ' ,. showing stellate prolongations 01 the 



dochrome; and the process oi cell-multiplication nuc i ei 

 is effected by the subdivision of this matter into 



two distinct masses, around each of which a pellucid cell-membrane subse- 

 quently makes its appearance, thus forming two new cells within the parent. 

 By a repetition of the same process, each of these new cells may again pro- 

 duce two new ones ; and thus the multiplication may be rapidly effected. 



Fiz. 16. 



Hematococcus binalis, in various stages of devel. 

 opment; a, a, simple rounded cells; b, elongated 

 cell, the endochrome preparing to divide ; c, c, cells 

 in which the division has taken place ; d, large pa- 

 rent cell, in which the process has been repeated 

 a second time, so as to form a cluster of four se- 

 condary cells, such as is often seen in Cartilage. 



Coceochloris cystifera, showing various stages of 

 development: a, simple globular cells, surround- 

 ed by a well-defined mucous envelope ; b, elon- 

 gated cell about to divide; c, cell doubled by (di- 

 vision, both the new cells still enclosed in original 

 mucous envelope ; rf, further stage of the same 

 process, one of the secondary cells having agai:i 

 divided, whilst the other has not yet undergone 

 this change, but is about to do so ; e, group of 

 cells formed by the same process, and still re- 

 tained within the original mucous envelope. 



This form of cell-development is best seen in some of the simplest Alga\ 

 which consist of isolated cells, and in which the individuals composing the 

 successive generations are quite independent of one another ; and we have a 

 good illustration of it in the Hematococcus binalis, whose various stages ol 

 cell-multiplication are shown in Fig. 15. In many other instances, the cells 

 of successive generations, without losing their individuality, are held together 



