THE CELL AND PROTOPLASM. 95 



appears to be in most intimate connection with 

 the center of cell life. In the activities which 

 characterize cell life this centrosome appears to 

 lead the way. From it radiate the forces which 

 control cell activity, and hence this centrosome is 

 sometimes called the dynamic center 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 biological discussion it will be 

 only necessary to notice some of the activities 

 of the cell. Of the four fundamental vital prop- 

 erties of cell life the one which has been most 

 studied and in regard to which most is known is 

 reproduction. This knowledge appears chiefly un- 

 der 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 reproduction is thus cell division, 

 and if we can comprehend 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 fol- 

 lowing description will outline the general facts 

 of such cell division, and will apply with consid- 

 erable accuracy to all cases of cell division, al- 

 though the details may differ not a little. 



