56 



CELL-DIVISION 



was to preside over cell-division. " The centrosome is an indepen- 

 dent permanent cell-organ, which, exactly like the chromatic elements, 

 is transmitted by division to the daughter-rr/A-. The centrosome rep- 

 resents the dynamic centre of the cell." ^ This view has been widely 

 accepted by later investigators, and the centrosome has been shown 

 to occur in a large number of adult tissue-cells during their resting 

 state ; for example in pigment-cells, leucocytes, connective tissue- 

 cells, epithelial and endothelial cells, in certain gland-cells and nerve- 

 cells, in the cells of many plant-tissues, and in some of the unicellular 



Fig. 23. — Final phases (telophases) of mitosis in salamander cells. [FlemmiNG.] 

 /. Epithelial cell from the lung; chromosomes at the poles of the spindle, the cell-body divid- 

 ing; gianules of the "mid-body" or 7.ivischenkdiper v.i the equator of the disappearing spindle. 

 y. Connective-tissue cell (lung) immediately after division ; daughter-nuclei reforming, the cen- 

 trosome just outside of each ; mid-body a single granule in the middle of the remains of the 

 spindle. 



plants, and animals, such as the Diatoms and Flagellates. That 

 the centrosome gives the primary impulse to cell-division by its own 

 division has, however, been disproved ; for there are several accu- 

 rately determined cases in which the chromatin-elements divide 

 long before the centrosome, and it is now generally agreed that the 

 division of chromatin and centrosome are two parallel events, the 

 causal relation between which still remains undetermined. (Cf. 



P- 77 ■) 



1 Boveri, '87, 2, p. 153. 



