i REPRODUCTION 19 



thing more than this is necessary. Amoebae are subject to 

 all sorts of casualties ; they may be eaten by other organ- 

 isms or the pool in which they live may be dried up ; in one 

 way or another they are constantly coming to an end. 

 From which it follows that if the race of Amoebae is to be 

 preserved there must be some provision by which the 

 individuals composing it are enabled to produce new in- 

 dividuals. In other words Amoeba must, in addition to its 

 otjier functions, perform that of reproduction. 



An Amoeba reproduces itself in a very simple way. The 

 nucleus first divides into two : then the whole organism 

 elongates, the two nuclei at the same time travelling away 

 from one another : next a furrow appears across the middle 

 of the drawn-out body between the nuclei (Fig. i, I; fig. 2, 

 C, D) : the furrow deepens until finally the animalcule sepa- 

 rates into two separate Amoebae (Fig. 2, E), which hence- 

 forward lead an independent existence. 



This, the simplest method of reproduction known, is called 

 simple or binary fission. Notice how strikingly different it 

 is from the mode of multiplication with which we are 

 familiar in the higher animals. A fowl, for instance, multi- 

 plies by laying eggs at certain intervals, in each of which, 

 under favourable circumstances, and after a definite lapse of 

 time, a chick is developed : moreover, the parent bird, after 

 continuing to produce eggs for a longer or shorter time, dies. 

 An Amoeba, on the other hand, simply divides into two 

 Amoebae, each exactly like itself, and in doing so ceases to 

 exist as a distinct individual. Instead of the successive 

 production of offspring from an ultimately dying parent, we 

 have the simultaneous production of offspring by the divi- 

 sion of the parent, which does not die, but becomes simply 

 merged in its progeny. There can be no better instance of 

 the fact that reproduction is discontinuous growth. 



C 2 



