CHAPTER IV. 



THE FOEMATION OP NEW CELLS. 



43. — There are two essent'ally different ways in which 

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

 body into two or more bodies ; (3) 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, Eig 25), which are naked masses 

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

 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 welt-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 



S 



Fig. 35. — Division of the 

 swarm-spores of Cfiondnoder- 

 madifforme: a, withnucleas ; 

 6, nncleua diegolved ; c. two 

 nuclei, divisioTi of protoplaam 

 begun ; d, e,/, compli-tion of 

 the process.— After DeBary. 



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



