344 SCIENCE PROGRESS 



the drop, and to the inductive effect of the position of these 

 outer lines on those within. 1 In a large cell the outermost 

 spindle-threads may be quite remote from the cell-boundary; 

 and, as we have seen, the threads are continuous across the 

 equator, which is an impossibility in Leduc's model. 



Gallardo, adopting a mode of experimentation suggested by 

 Guebhardt, places two like poles of a battery on a horizontal 

 metal plate in an electrolyte, and, midway between them, two 

 wide strips of metal connected with the opposite pole, in the 

 position of the already split equatorial nuclear plate (fig. i, g). 

 In this case electrolytic deposit takes place on the basal metal 

 plate in successive zones corresponding to equipotentials, and 

 the lines of force may be drawn by a series of curves cutting 

 the zones at right angles — in terms of geometry the " orthogonal 

 trajectories " of the equipotential zones. These lines of force so 

 drawn form two half-spindles, centring on the two like poles, 

 and with their bases resting on the strips of metal connected 

 with the opposite pole. Here it is the presence of the strips 

 that alters the distribution of the lines of force so as to make 

 them simulate two halves of a spindle, and here again the spindle 

 is interrupted in the centre. Though these two models give an 

 approximate representation of the cell-figure at the moment 

 of the splitting of its equatorial plate, yet even for this state 

 they take no account of its continuous fibres from pole to pole, 

 nor of the origin and growth of the cell-spindle as a true spindle 

 from its first appearance. The two models are pretty paradoxes : 

 they are nothing more. 



It is always well to assume that capable workers have not 

 gone astray without some good reason for their deviation. 

 Why, then, should biologists again and again have sought to 

 ignore the true bipolar character of the cell-spindle ? One reason 

 is the fascination of simplicity : they have sought to explain 

 the complicated process of mitosis and of cell-division by a 

 single series of forces. But still more important is one real 

 difficulty arising in the " dual force " explanation that we have 

 not yet touched. One necessary result of a spindle centred on 

 two opposite poles is to tend to draw these two poles together, 

 and to deform the cell into a biconcave disk like the red blood 



1 The distribution of stream-lines and of lines of force, etc., is always such as 

 it would be if they repelled their neighbours— as if they exerted a pressure at right 

 angles to their direction. 



