THE PROTOZOA THE DAWN OF LIFE 5 



two, binary fission as it is called, that reproduction or multiplica- 

 tion chiefly takes place in the Amoeba and many of the Protozoa. 

 It is hardly exact to call the two resulting Amoebae the children 

 of the original, for they are simply the original Amoeba cut in 

 halves ; it is convenient, however, to speak of these products of 

 binary fission as " daughter-cells." 



The new Amoebae absorb and assimilate food, thus adding new 

 material to the original matter of the parent body, and then each 

 of them again divides into two. So the process of food assimila- 

 tion, growth, and subsequent division is repeated again and again, 

 an ever lessening part of the actual body substance of the original 

 ancestor being passed on to each succeeding generation. It is 

 obvious, therefore, that an Amoeba never dies a natural death, 

 or, to put it another way, " no Amoeba ever lost an ancestor by 

 death." An Amceba may be killed outright, but in that case it 

 leaves no descendants ; but if it once produces new Amcebae, it 

 never dies, although it ceases to exist as a single individual. 



Occasionally, two Amcebae may be seen to flow towards each 

 other, and fuse in a way which may be considered as an incipient 

 form of sexual union, and this fusion acts undoubtedly as a re- 

 vivifying process or " rejuvenescence," arresting that constitu- 

 tional weakening which seems to be set up by, and the inevitable 

 result of repeated fission. 



As Professor F. W. Gamble states, (t simple division carried 

 beyond a certain number of cleavages appears to be ineffective. 

 The process, though long, is not endless, and after a time it slows 

 down and ceases. Exactly why it should do this is not very clear, 

 but it would seem that the slackening is not due to deterioration 

 of the environment so much as to some constitutional weakening. 

 Any weakness is, owing to the simple cleavage of one into many, 

 conveyed to the descendants, and there seems to be no rectifying 

 property. It has been found that if such a strain or culture, the 

 members of which are derived from a single Protozoon by re- 

 peated fission, is isolated, it gradually dwindles and dies. If, 

 however, it is allowed access to another culture of exactly similar 

 appearance, it undergoes renewal of this dividing property, and 

 after an interval once more populates the water." 



From the above brief description of the Amceba, it will be 

 seen that although this interesting and remarkable organism is 



