94 GENERAL BIOLOGY 



Something like this takes place in the process of 

 indirect cell division, at least so far as the nucleus is 

 concerned. 



The greater part of cell life is passed in the so- 

 called "resting stage," in which the chromatin sub- 

 stance is scattered through the nucleus apparently 

 in the form of granules. When a cell is preparing to 

 divide, these granules begin to aggregate and fuse 

 together (or at least appear to do so, though it is 

 claimed by some that each granule retains its in- 

 dividuality). By such an aggregation the chroma I in 

 assumes the form of a tangled thread or skein. 1 This 

 later segments into a number of separate bodies to 

 which the name chromosome is given. The number 

 of such chromosomes, which varies from one or two 

 to a hundred or more in each cell, is normally always 

 constant in any one species. Sometimes they even 

 reveal individuality in relative size and shape. At 

 the same time that these nuclear changes arc taking 

 place there may be observed in the cytoplasm a 

 tiny dot surrounded by a mass of radiations. This 

 structure is appropriately termed the aster and the 

 central body the centrosome. This appears to de- 

 velop about a central granule, the centriole. The 

 centrosome divides and the two halves move apart 

 about the nucleus, each apparently carrying a por- 

 tion of the aster with it, until they have placed 

 themselves on opposite sides of the nucleus. They 

 are connected with each other by the rays of the 

 divided aster so as to produce what, from its appear- 



1 Whence the name mitosis, from /J.LTOS. 



