14 



ZOOLOGY 



SECT. 



halves the nucleus has also divided, and each of the two new 

 Amcebai possesses a nucleus similar to the original one, 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 repro- 

 duction or multiplication takes place in the Amoeba. 



In spite of the great simplicity of its structure, the Amoeba 

 thus carries on a number of different functions. The practically 

 structureless particle of protoplasm, is able to act on matter 

 absorbed as food in such a way as to alter the chemical composition 

 of the latter and to assimilate it ; it is able to carry on movements 



FIG. 2. Amoeba polypodia in successive phases of division. The lii;ht spot is the contractile 

 vacuole ; the dark the nucleus. (From Lang's Text-Book, after F. E. Schulze.) 



of locomotion, as well as movements those involved in the 

 taking in of food-particles which may be looked upon as move- 

 ments of prehension ; it exhibits a certain degree of sensitiveness 

 or irritability, as shown by the modifications of its movements 

 which result from contact with foreign bodies ; it is able to 

 respire ; it carries on processes of excretion ; and, finally, it is 

 capable of reproducing its kind. It is these functions that charac- 

 terise living beings as distinguished from non-living matter. 

 What is specially characteristic of the living organism in general 

 when compared with a non-living object is the capacity of the 

 former to respond by changes in itself to influences operating on 



