I REPRODUCTION 237 



appears certain that " death has no place as a natural re- 

 current phenomenon " in that organism. In multicellular 

 form it is only the reproductive cells which are, physically, 

 potentially immortal. 



It is said that occasionally two Amoebae come into contact 

 and undergo fusion, just as the gametes of the frog (sperm 

 and ovum) unite in the processes of fertilisation (p. 197). 

 This process of conjugation which probably precedes en- 

 cystment and multiple fission (p. 233) will be referred to 

 again in the following chapters, and it is important to bear in 

 mind that reproduction can take place quite independently of 

 such a process. 



Amoebae may also be propagated artificially. If a speci- 

 men is cut into pieces, each fragment is capable of develop- 

 ing into a complete animalcule provided it contains a 

 portion of nuclear matter, but not otherwise. From this it 

 is obvious that the nucleus exerts an influence of the utmost 

 importance over the vital processes of the organism. 



If an Amoeba does happen to be killed and to escape 

 being eaten it will, like a dead frog, undergo gradual decom- 

 position, becoming converted into various simple substances 

 of which carbon dioxide, water and ammonia are the chief 



(P- I 5 2 )- 



Death results if the temperature to which an Amceba is 

 exposed reaches about 40 C., and at freezing point its move- 

 ments cease entirely and it becomes inert. 



We thus see that complex organs, composed of various 

 tissues, each consisting of cells of characteristic form, are 

 not necessary in order that the vital functions may be 

 performed : the only essential is nucleated protoplasm. As 

 we pass from the unicellular Amceba to the higher multi- 

 cellular animals we shall find just as we found in tracing 



