CHAPTER IV. 



THE FORMATION OF NEW CELLS. 



43. There are two essentially different ways in which 

 cells originate, viz., (1) by the division of a protoplasmic 

 body into two or more bodies ; (2) by the union of two or 

 more protoplasmic bodies. 



44. Cell-Formation by Division. The simplest cases of . 

 the formation of cells by division occur in the Myxomy- 

 cetes. The swarm-spores (a, Fig 25), which are naked masses 

 of freely moving protoplasm, first lose their nuclei (as in I), 

 and then become constricted (as at c) ; the constriction 

 deepens, and finally divides each mass 

 into two parts (d, e,f). 



45. This may be taken as the 

 type of cell-formation by division, 

 and in no case does it differ in any 

 essential particular from this. Most 

 plant-cells, however, are surrounded 

 by a wall, whose deportment during 

 division enables us to distinguish two 

 more or less well-marked modes of 

 cell-formation by division. On the 

 one hand the wall divides as well as the protoplasm (Fission), 

 while on the other the wall takes no part in the division, and 

 it is only the protoplasm which divides (Internal Cell-For- 

 mation}. 



46. The best examples of Fission are to be seen in those 

 unicellular plants which have been frequently described 

 under the name of Protococcus.* "The cell elongates and 

 the protoplasm divides into two across its longer axis, and 



ma difforme ; a, with nucleus ; 

 b, nucleus dissolved ; c. two 

 nuclei, division of protoplasm 

 begun ; d, e,f, completion of 

 the process. After DeBary. 



* See "Huxley and Martin's Biology," Chap. II. 



