I MULTIPLICATION 237 



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

 current phenomenon " in that organism. 



It is said that occasionally two Amccba come into contact 

 and undergo complete fusion, just as the gametes of the frog 

 (sperm and ovum) unite in the processes of fertilization-, 

 (p. 197). This process of conjtigation has been more accu- 

 rately observed in other unicellular organisms (pp. 268 and 

 278), and it is important to bear in mind that reproduction can/ 

 take place in all these quite independently of such a process.' 



Amccba 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 Amceba 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 substan- 

 stances of which carbon dioxide, water and ammonia are the 

 chief (p. 152). 



Death results if the temperature to which an Amceba is 

 exposed reach about 4o°C., and at freezing point its move- 

 ments cease entirely and it becomes inert. 



\\& 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 Amoeba to the higher multi- 

 cellular animals we shall find — just as we found in tracing 

 the development of the frog from the unicellular oosperm 

 (p. 206), — that a. differentaiion of structure accompanied by a 

 division of physiological labour becomes more and more 



