CYTOLOGY 327 



The division is generally equal, so that the two daughter nuclei are approxi- 

 mately of the same size. Not infrequently during division the nucleus 

 becomes much elongated, while the halves of the divided karyosome occupy 

 the poles and are connected by a fine line, which is usually referred to as 

 the centrodesmose, and is supposed to connect the two daughter centrioles 

 which may be presumed to lie embedded in the daughter karyosomes. This 

 is all the more striking in cases which have sometimes been noted where the 

 chromatin of the nucleus, instead of being concentrated into a single karyo- 

 some, is in the form of two or more granules lying on the inner surface of 

 the nuclear membrane. At nuclear division, a small central granule first 

 divides, and the two separating halves are connected by a fibre. The 

 chromatin granules themselves then divide into two groups, and two 

 daughter nuclei are ultimately formed. In these cases the central 

 granule, which may or may not be a true centrosome, is not obscured by 

 concentration of the chromatin around it in the form of a karyosome. 

 In other cases it would seem that the central granule divides, and the 

 halves, still connected by a fibre, separate, and eventually pass out of 

 the karyosome, the division of which is retarded. There is then produced 

 an elongated nucleus with a granule at each end, and a centrodesmose 

 connecting them. The karyosome, still undivided, lies at the centre of 

 the centrodesmose. Though the gradual elongation and constriction of 

 a uniformly staining karyosome is the usual appearance in nuclear division, 

 a number of observers have maintained that after appropriate staining 

 the elongating karyosome can be resolved into a spindle, upon the fibres 

 of which the chromatin is distributed in the form of granules or chromo- 

 somes. Schaudinn (1904) described a mitotic division of the nucleus in 

 Trijpanosoma noctucB ; Rosenbusch (1908-09) in T. lewisi and T. brucei ; 

 Hindle (1909) in T. dim.orphon ; Chagas (1909) in T. cruzi ; Alexeieff (1912e) 

 in T. lewisi and T. brucei; Kuhn and Schuckmann (1912), Kuczynski 

 (1917), and Schuurmans-Stekhoven (1919) in T. brucei; Hartmann and 

 Noller (1918) in T. theileri ; and Nieschulz (1922a) in bird trypanosomes. 

 Hartmann and Noller state that in the case of T. theileri there is formed 

 an intranuclear spindle which appears to originate in the achromatic 

 material of the karyosome, while the chromatin substance in the form of 

 granules is first distributed irregularly on the spindle (Fig. 156, 5-8). The 

 spindle elongates, as also does the nuclear membrane, so that there results 

 a long oval nucleus enclosing a sharp-pointed spindle, the ends of which 

 may rest on the nuclear membrane. At this stage the chromatin granules 

 collect at the equator of the spindle to form an equatorial plate, which 

 quickly divides into daughter plates. The latter move towards the poles 

 of the spindle, wdiich divides at its centre. Each half, with the chromatin 

 granules of the daughter plate, which have again become irregularly dis- 



