THE DIVIDING CELL 333 



boundary between spindle and asters, for the rays of the latter 

 ultimately curve in to meet their fellows of the opposite side, 

 though it may be at an infinite distance. 



It is obvious that in the cell the original extranuclear spindle 

 is formed on the pattern of our present field, constituting a "true 

 spindle," centred on two poles of " opposite sign." Hence, until 

 it can be shown that at some period in the process of mitosis a 

 reversal occurs at one or other pole — a supposition which has 

 no shadow of evidence for its formation — we must conclude that 

 the cell-spindle through all its stages is the expression of a dual 

 force centring on the two centrosomes, which are of opposite 

 signs. This at once disproves theories based on conditions 

 assumed to be similar at both centres : (1) Butschli's and 

 Rhumbler's theory of like osmotic tensions of the alveolar 

 cytoplasm around the two centrosomes ; (2) Leduc's later view 1 

 of diffusion currents centring similarly about both centrosomes ; 

 (3) Frank R. Lillie's and Gallardo's later view of similar electro- 

 static charges on the two centrosomes of opposite sign to the 

 intervening structures (including the chromosomes). 



For our next step we must analyse the true nature of 

 Faraday's lines of force, to see what they are and what they 



1 Leduc's earlier view was as follows : he found that visible diffusion currents 

 pass in a solution between a centre of concentration and one of dilution, and that 

 these follow the lines of a bipolar spindle. Thus into a drop of dissolved saltpetre 

 lying flattened on a slide, and containing light bodies such as blood corpuscles in 

 suspension, he introduced at one end a crystal of the substance and at the other a 

 droplet of water, and obtained a beautiful spindle, which he photographed. That 

 this explanation cannot apply to cell mitosis is certain, for the osmotic phenomena 

 are of like kind in both centrosomes of the cell. This is admirably demonstrated 

 in the gigantic cell-figures of the little marsh-worm, Rhynchelmis, which in the 

 segmenting egg are just visible to the myopic eye, and whose changes have been 

 fully worked out and portrayed with absolute accuracy by Vejdowsky and Mrazek. 

 I have had the honour of being allowed to control the figures by inspection of the 

 original specimens through the great kindness of these authors. Leduc, having 

 been convinced by this reasoning, put forward the second hypothesis which we 

 have just dismissed as equally untenable. Rhumbler attempted to demonstrate 

 the kinematic paradox that a field centring on two " like " centres might, under 

 certain circumstances, assume the " spindle " character. He placed a hexagonal 

 elastic network on a ring over a flat plate, and through two holes pulled down the 

 network, and found that the middle row, one mesh wide, was narrower next the 

 centres of traction and wider in the centre, resembling a spindle. This appearance 

 is a necessary consequence of the coarse structure of the net — it is a mere 

 "grain structure." But looking outside this central row, we see at once that 

 the general lines of tension form a figure which is essentially that of the crossed 

 field or antispindle. 



