OF THE CELL THEORY 171 



This very brief and imperfect account must 

 suffice to indicate the lines along which investiga- 

 tion is at present advancing, in the attempt to 

 determine the nature of the processes which go on 

 within active living protoplasm. 



Turning now to the nucleus, we find that an 

 extraordinary number of minute researches have 

 been made of late years, more especially with a 

 view to determine as far as possible the part 

 played by the nucleus in the acts of fertilisation 

 and reproduction, in the hope of obtaining some 

 clue to the attractive but bewildering problem of 

 heredity. The important part played by the 

 nucleus in initiating, indeed determining, the act 

 of cell-division, was first definitely established by 

 F. E. Schulze, in Amceba polypodia. He describes 

 the successive changes as follows : The nucleus 

 first elongates, then becomes dumb-bell shaped ; 

 then the bridge between the two knobs becomes 

 thinner and thinner, and finally breaks, so that 

 there are now two separate nuclei, formed by 

 division of the single original one. Next, the 

 body of the Amceba begins to elongate in the 

 same direction as the nucleus did previously ; then 

 follow constriction, and finally the division of 

 the Amceba into two parts, each containing one of 

 the two nuclei already formed. The entire pro- 

 cess occupied ten minutes ; division of the nucleus 

 taking about a minute and a half, and the remain- 

 ing eight and a half minutes being occupied by 

 division of the body of the Amceba. A similar 

 process of direct nuclear division, as it is called, 



