558 Dr. M. Hartog. [ Dec. -1, 
lag imposed by the viscidity of the medium (fig. 14); it is interesting 
to see how they often become ruptured into a series of short lengths 
which individually lag more than the chains as a whole. Such figures 
represent approximately the axial section of a bipolar field, of which the 
polar areas are subjected to equal and opposite torsions. We use melted 
jelly or balsam to obtain a figure whose changes during revolution are 
arrested by its solidification, so as to allow of its being preserved and photo- 
eraphed. The interlacings of chains are especially well shown in some of 
these “torsion ” figures. 
X. 
The distribution of the chains of force in the cell is very imperfectly 
represented by the classical figures of the magnetic field of two “ unlike” 
poles hitherto utilised ; for these always depict the axial portions of fields 
of indeterminate extension. They have hence the character that the 
lines tend to pass from one pole to the other without deflection, and so 
form a series of curves all concave to the interpolar axis—the straight 
continuations of this axis being supposed to meet at infinity. Now the 
chains in the cell are differentiated into (1) “astral rays,” radiating more 
or less directly outwards from the centres, and usually nearly straight 
or even convex to the interpolar axis, but concave to its prolongations ; 
and (2) the spindle-fibres extending from pole to pole, and concave to the 
interpolar axis. 
We can make a far more exact magnetic model than the common one, if 
we limit the field by an envelope of highly permeable material; for which 
purpose I use a sheet of charcoal-iron with an oval window, like a 
photographer’s vignette-mask. We now see the chains radiating from the 
pole outwards, straighten out, or even become convex to the interpolar axis 
and concave to its prolongation, thus turning their backs on the spindle-fibres 
(figs. 7, 8, 15). In the cell the rays appear straight most frequently, but 
the back-turned (adossé) condition is often seen and figured. The analogy of 
this model would lead us to infer that the “Hautschicht” of the cell is 
highly “permeable ” to mitokinetic force. 
A still closer approximation to the character of the mature dumbbell figure 
of the animal cell is seen in glycerine or other viscid media, when we allow 
the magnetic stress to continue after the first segregation has taken place 
(figs. 9 and 10). Thechains, like other permeable bodies, tend to place them- 
selves in the strongest part of the field. Consequently, the interpolar chains 
move laterally in towards the axis, shortening up as they do so by the 
squeezing out of the liquid in the interstices between consecutive particles 
and adjacent strands. Since this action lessens as we recede from the neigh- 
