1258 



PHYSIOLOGY 



the cells contain only two or four chromosomes. All these changes, which are included 

 under the term mitosis or karyokinesis, seem to be adapted to ensuring an equal qualita- 

 tive as well as quantitative distribution of the nuclear chromatin among the daughter 

 cells resulting from the division of any cell. As we have seen in an earlier chapter, 

 the nucleus, by its interaction with the cytoplasm, determines the processes of assimila- 



Fia. 568. Diagram showing the changes which occur in the centrosomes 



and nucleus of a cell in the process of mitotic division. (SCHAFER.) 



The nucleus is supposed to have four chromosomes. 



tion and growth of the whole cell. For the preservation of type in cell division it is 

 therefore essential that the nuclei of the daughter cells shall be identical in all respects 

 with the nucleus of the mother cell. 



Sexual reproduction involves the conjugation of two cells, with union 

 of their nuclei. If each of these nuclei consisted of the normal number of 

 rlmmiosomes, the fertilised egg cell would contain double the number 



