DETAILS OF MITOSIS 



91 



hemispherical ''end-plate" or *' pole-plate " is situated at either pole 

 of the spindle, and Hertwig's observations indicated, though they 

 did not prove, that these plates arose by the division of a large 

 "nucleolus." Nearly similar pole-plates were somewhat described by 

 Schewiakoff ('88) in Eiiglypha (Fig. 39), and it seems clear that they 

 are the analogues of the centrosomes or attraction-spheres in higher 

 forms. In Euglcna, as shown by Keuten, the pole-plates, or their 

 analoo-ues, certainly arise by division of a distinct and persistent intra- 

 nuclear body ("nucleolus" or " nucleolo-centrosome ") which elon- 



Fig. 40. — Mitosis in the flagellate, Eugleua. [KEUTEN.] 

 A Preparing for division ; the nucleus contains a " nucleolus " or nucleolo-centrosome sur- 

 rounded Ty a g-up of chromosomes. B. Division of the ;• nucleolus to form an mtranuclear 

 spindle. C. Later stage. D. The nuclear division completed. 



gates to form a kind of central spindle around which the chromatin 

 elements are grouped (Fig. 40); and Schaudinn ("95) described a 

 similar process in Am(^ba. Richard Hertwig's latest work_ on 

 Infusoria ('95) indicates that a similar process occurs m the micro- 

 nuclei of Paramcccinm, which at first contain a large " nucleolus 

 and afterward a conspicuous pole-plate at either end ot the spindle 

 (Fio- :;8 D-H\ TJie origin of the pole-plates was not, however, 

 po^tively determined. A corresponding dividing body is foupd m 

 Ccratiinn (Lauterborn, '95), and as in the Infusoria the entire 

 nucleus transforms itself into a fibrillar spindle-like body. 



