1 8 MANUAL OF ZOOLOGY sect. 



and developed from it by division. It is mainly by this 

 simple process of division into two, or binary fission, as it is 

 called, that reproduction or multiplication takes place in the 

 Amceba. 



Fig. 2. — Amoeba polypodia in successive phases of division. The light spot is the 

 contractile vacuole; the dark the nucleus. (From Lang's Text-Book, after 

 F. E. Schulze.) 



Amceba thus consists of an undivided particle of proto- 

 plasm containing a nucleus. To such a particle the term 

 cell is applied. In higher groups the animal when fully 

 developed, consists of a number of such cells, usually differ- 

 ing in character in different parts ; and simple animals, such 



