184 ON THE INTERNAL FORM AND [ch. 



words, if, when situated in this region, the permeabihty of the 

 bodies is not very much in excess of that of the medium. 



Let the poles now tend to separate farth-er and farther from 

 one another, the strength of each pole remaining unaltered ; in 

 other words, let the centrosome-foci recede from one another, as 

 they actually do, drawing out the spindle-threads between them. 

 The loci F^, F^,, will close in to nearer relative distances from the 

 poles. In doing so, when the locus F„ crosses one of the bodies, 

 the body may be torn asunder; if the body be of elongated shape, 

 and be crossed at more points than one, the forces at work will 

 tend to exaggerate its foldings, and the tendency to rupture is 

 greatest when F„ is in some median position (Fig. 56). 



When the locus F^ has passed entirely over the body, the body 

 tends to move towards regions of weaker force ; but when, in 



Fa 



Fig. 5n. 



turn, the locus F^, has crossed it, then the body again moves towards 

 regions of stronger force, that is to say, towards the nearest pole. 

 And, in thus moving towards the pole, it will do so. as appears 

 actually to be the case in the dividing cell, along the course of 

 the outer hues of force, the so-called "mantle-fibres" of the 

 histologist*. 



Such considerations as these give general results, easily open 

 to modification in detail by a change of any of the arbitrary 

 postulates which have been made for the sake of simplicity. 

 Doubtless there are many other assumptions which would more 

 or less meet the case; for instance, that of Ida H. Hyde that, 



* We have not taken account in the above paragraphs of the obvious fact that 

 the supposed symmetrical field of force is distorted by the presence in it of the 

 more or less permeable bodies; nor is it necessary for us to do so, for to that 

 distorted field the above argument continues to apply, word for word. 



