RESEARCHES ON KARIOKINESIS AND CELL DIVISION. 41 



two dimensions, not of three, as in Flemming's description ; 

 lie considers them to occur after the mass of fibrils has been 

 compressed into the equatorial plane. He states, too, that 

 the central points of the daughter nuclei may separate before 

 the fibrils have divided into loops, a division of the fibrils in 

 the equatorial plane occurring subsequently. Fleraming 

 has observed in the cells of the testes of Salamander " cask 

 forms," in which the fibrils were continuous across the 

 equator; but he believes this to be the consequence of tem- 

 porary fusion of the ends of fibrils previously separate; for 

 in earlier stages there were distinct loops only half as long 

 as the cask figure. 



H"uclear Spindle. — The nuclear spindle, first described by 

 Biitschli,^ is most conspicuous in the dividing cells of plants 

 and segmenting ova; it is formed of faint striae passing 

 between two poles, situated at equal distances from the equa- 

 torial plate ; frequently at each pole there is a radiating figure 

 or " sun,'^ composed of faint strise, like those of the spindle. 

 The spindle and suns are well shown in figs. 16 — 19 from the 

 segmenting ovum of Toxopneustes liviclus. Flemming con- 

 siders the spindle to consist of achromatin, and therefore to 

 belong to the nucleus, while Strasburger," with whom Klein 

 agrees, believes that it belongs to the cell protoplasm. It 

 is more probable that the suns at the poles of the spindle 

 are parts of the cell substance. This is proved for the ova 

 of Echinoderms by Flemming's figures in the third part of 

 his ' Beitrage.' Strasburger gives a typical figure of a 

 dividing nucleus with polar suns, spindle, and equatorial 

 plate, from the embryo sac of Viola palustris (ref. op. cit., 

 Taf. ii, fig. 33). 



i|: The descriptions of other observers do not resemble 

 those of Flemming in giving such definite forms to the 

 chromatic constituents of the nucleus. Schleicher^ re- 

 presents the chromatic elements in the cartilage cells 

 of Batrachian larvse as irregular granules and rods, 

 with a general tendency to lie parallel to the axis of 

 the spindle. These, when they begin to form the daughter 

 nuclei, fuse together into clumps of chromatic sub- 

 stance, which subsequently again break up into rods and 

 granules. Figs. 27, 28, and 29, which are successive 

 stages, illustrate this ; figs. 30 and 31, from the cranial 

 cartilage of a toad, show the achromatic striae more 

 clearly. 



Definite Number of the Chromatic Loops.— In three cases of 



' ' Zeitschr. Wiss. Zool.,' vol. 25, 1S75. 

 ' Zelibildung u. Zelllheiluug,' 1850, p. 328, 



