
1904. | The Dual Force of the Dividing Cell. 557 
out from either centre will frequently extend beyond the equator of 
the cell, into what we may term the “domain” of the other centres 
here such crossings are especially common, and occur when the direction 
of the rays is approximately straight. From this we may infer that the 
_ reluctivity to the mitokinetic force of the undifferentiated protoplasm and 
its inclusions is very high, so that the rays are but little affected by that 
centre to which they are not as yet organically attached. As soon as two 
ruys from opposite centres actually meet and join, their straightness passes 
into a curve concave to the intercentral axis. 
The comparison between the cellular and the magnetic chains can be but 
an imperfect one at best, on account of the different ways in which they 
are formed respectively: the magnetic chains are formed simultaneously* by 
segregation along their whole course, and the cell-chains by progressive 
outgrowth from the centres. All the same, we have seen that the crossings 
and interlacings, which have been invoked as incompatible with magnetic 
analogies, are actually produced in our magnetic model, and their presence 
in the cell-figure is no argument against the kinetic nature of the cell- 
spindle, or the dual nature of the cell-stresses. Take, on the other hand, 
the assumption that the fibres are the transmitters of a mechanical push or 
pull: they are imbedded in viscid protoplasm, so that by friction they would 
communicate their motion thereto. Thus, where crossing occurred, the 
motions of the adjacent crossing fibres would be mutually transmitted, and 
would effect lateral displacements which have been neither figured nor 
recorded, and which it is safe to conclude do not exist in the cell. In this 
respect, therefore, the crossings of the astral rays tell equally against both 
of the mechanical explanations of the cell-figure, while they are actually 
reproduced in our magnetic model. 
IX. 
In certain cellular fields, notably in the segmentation-cells of the Slug 
(Zimax) described and figured by Mark in 1879, the cell-fibres diverge in 
spirals from the poles. This is one of many proofs that forces other than, 
and additional to, the centred mitokinetic force, are operative in the 
dividing cell. Here, again, we see the contrast between the behaviour of 
lines of force in a homogeneous medium and our material chains of force. 
If we rotate in our field of two unlike poles the glass plate covered with 
viscid mixture, we see the chains become sigmoid or shaped, owing to the 
* I speak only of the conditions under which I have experimented. If the poles were 
remote, and the. magnetomotive force long maintained, I should not doubt that the 
magnetic chains would grow out from the poles. 
