106 THE STORY OF LIFE'S MECHANISM. 



presence of a nucleus was not necessary to 

 constitute a cell. A German naturalist recog- 

 nized among lower animals one group whose 

 distinctive characteristic was that they were 

 made of cells without nucleii, giving the name 

 Monera to the group. As the method of study- 

 ing cells improved microscopists learned better 

 methods of discerning the presence of the 

 nucleus, and as it was done little by little they 

 began to find the presence of nucleii in cells in 

 which they had hitherto not been seen. As 

 microscopists now studied one after another of 

 these animals and plants whose cells had been 

 said to contain no nucleus, they began to find 

 nucleii in them, until the conclusion was finally 

 reached that a nucleus is a fundamental part of 

 all active cells. Old cells which have lost their 

 activity may not show nucleii, but, so far as we 

 know, all active cells possess these structures, 

 and apparently no cell can carry on its activity 

 without them. Some cells have several nucleii, 

 and others have the nuclear matter scattered 

 through the whole cell instead of being aggre- 

 gated into a mass; but nuclear matter of the 

 cell must have to carry on its life. 



Later the experiment was made of depriving 

 cells of their nucleii, and it still further emphar 

 sized the importance of the nucleus. Among 

 unicellular animals are some which are large 

 enough for direct manipulation, and it is found 

 that if these cells are cut into pieces the different 

 pieces will behave very differently in accordance 

 with whether or not they have within them a 

 piece of the nucleus. All the pieces are capable 



