THE CELL AND PROTOPLASM. 113 



control cell activity, and hence this centrosome is 

 sometimes called the dynamic centre of the cell. 

 This leads us to the study of cell activity, which 

 discloses to us some of the most extraordinary 

 phenomena which have come to the knowledge 

 of science. 



FUNCTION OF THE NUCLEUS. 



To understand why it is that the nucleus has 

 taken such a prominent position in modern bio- 

 logical discussion it will be only necessary to 

 notice some of the activities of the cell. Of the 

 four fundamental vital properties of cell life the 

 one which has been most studied and in regard 

 to which most is known is reproduction. This 

 knowledge appears chiefly under two heads, viz., 

 cell division and the fertilization of the egg. Every 

 animal and plant begins its life as a simple cell, 

 and the growth of the cell into the adult is 

 simply the division of the original cell into parts 

 accompanied by a differentiation of the parts. 

 The fundamental phenomena of growth and re- 

 production are cell division, and if we can com- 

 prehend this process in these simple cells we 

 shall certainly have taken a great step toward 

 the explanation of the mechanics of life. During 

 the last ten years this cell division has been 

 most thoroughly studied, and we have a pretty 

 good knowledge of it so far as its microscopical 

 features are concerned. The following descrip- 

 tion will outline the general facts of such cell 

 division, and will apply with considerable ac- 

 curacy to all cases of cell division, although the 

 details may differ not a little. 

 H 



