
1904. | The Dual Force of the Diding Cell. 567 
poles of a dual force. As the diffusion, osmosis, and surface-tension 
phenomena are of similar character at the two poles of a cell, they cannot be 
the forces involved in the spindle. Non-polarised undifferentiated forces, such 
as gravity, produce not the spindle-figure, but the “ crossed field.” 
17. Since an isolated magnetic pole cannot exist (our model having simply 
served to show how the axial section of an imaginary field would behave), it 
is obvious that the cell-field, being in three dimensions, and with isolated 
unlike poles, cannot be due to magnetism. 
18. It is not impossible that the field may be produced by statical 
electricity, but for the present there is no proof thereof. 
EXPLANATION OF PLATES 9—11. 
(Glycerine) (jelly) means that the dust was suspended in glycerine or jelly respectively ; 
(dust) that magnetic dust was sifted on to paper, and figure obtained by tapping (see p. 555). 
Figs. 1 and 2.—(From Wilson, “The Cell, etc.,” ed. 2, 1902, figs. 25 and 26); (A) resting 
cell, two centrioles in centrosome ; (B) formation of spindle ; (C, D, E) further 
evolution of dumb-bell figure, and disappearance of nuclear wall to free 
chromosomes; (F) stage of “ equatorial plate” ; (G, H) splitting of chromo- 
somes and discession of sister-segments ; (I, 1) division of cell and recon- 
stitution of daughter-nuclei. 
Fig. 3.—After Vejdowsky and Mrdzek, in ‘Arch. Mikr. Anat.,’ vol. 62, 1903 ; stages of 
oosperm of /hynchelmis (fig. 3, a, b), appruximation and fusion of male and 
female gametonuclei; two successive zones of radiate centroplasm showing 
outside centrospheres ; (c, d) “segmentation” figures, stage of equatorial plate. 
Fig. 4.—-After same ; stages of discession of sister-segments of chromosomes, the centro- 
somes showed “ blobbed ” conditions. 
Fig. 5.—Microphotograph of same preparation as fig. 3, ¢ (Zeiss Ap. 8 mm., x 400 
reduced 4), showing the dumb-bell figure among dark-stained yolk spherules. 
Fig. 6.—(Glycerine.) Current reduced as soon as figure developed. Anastomoses frequent. 
Fig. 7.—(Glycerine.) After fig. 6 was taken, the magnetising current was again 
increased ; the lateral chains have drifted inwards and become denser, 
leaving “ Biitschli’s spaces” on either side ; numerous interlacings, and good 
differentiation of asters and spindle. 
Fig. 8.—Glycerine triaster of two opposite poles and core. 
Fig. 9.—(Glycerine.) Tetraster ; two poles and two cores alternating. 
Fig. 10.—(Dust.) Pentaster ; four consecutive unlike poles with core in centre and 
spindle connections everywhere equivalent to the summation of four triasters. 
Fig. 11.—(Dust.) Tetraster with central mass, or pentaster of four “like” surrounding 
a central opposite pole ; the spindles have been made clearer by sweeping 
away the intervening dust. . 
Fig. 12.—Unipolar figures, after Boveri, showing crescentic centrosome and circular 
nucleus. 
Fig. 13.—(Dust.) Model of 21; a crescentic plate over pole representing the centro- 
some; a disk in front of its concavity, the nucleus. 
Fig. 14.—(Jelly.) Torsion figures ; the arrows show direction of torsion. 
Fig. 15.—(Dust.) Model of blobbed centrosomes, with small iron discs in front of the 
poles (compare fig. 4). 

