I REPRODUCTION 19 



thing more than this is necessary. Amoebje 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 

 other 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 dif- 

 ferent it is from the mode of multiplication with which we 

 are familiar in the higher animals. A fowl, for instance, 

 multiplies 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 division of the parent, which does not die, but 

 becomes simply merged m its progeny. There can be i.o 

 better instance of the fact that reproduction is discontinuous 

 growth. 



c z 



