I REPRODUCTION 237 



it therefore appears certain that " death has no place as 

 a natural recurrent phenomenon " in that organism. 

 In multicellular forms it is only the reproductive cells 

 which are, physically, potentially immortal. 



It is said that occasionally two Amoebae come into con- 

 tact 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 encystment and multiple fission (see p. 233) 

 will be referred to again in the following chapters, 

 and it is important to bear in mind that reproduc- 

 tion can take place quite independently of such a process. 



Amoebae may also be propagated artificially. If a 

 specimen is cut into pieces, each fragment is capable 

 of developing 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 in- 

 fluence 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 

 decomposition, becoming converted into various simple 

 substances of which carbon dioxide, water, and ammonia 

 are the chief (p. 152). 



Death results if the temperature to which an Amoeba 

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

 movements 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 proto- 

 plasm. As we pass from the unicellular Amoeba to the 

 higher multicellular animals we shall find just as we 

 found in tracing the development of the frog from the 

 unicellular oosperm (p. 205) that a differentiation of 



