REPRODUCTION 59 



tion has been directed to this inquiry, and parti- 

 cularly by Professor Hartog, l who points out that 

 the spindle and the external radiations described 

 above make up a " strain-figure," like that of the 

 " lines of force " in relation to the poles of a magnet. 

 " Such/' he continues, " we can demonstrate in a 

 plane by spreading or shaking iron filings on a 

 piece of paper above the poles of a magnet, or in 

 space by suspending finely divided iron in a thick 

 liquid, such as mucilage or glycerine and bringing 

 the vessel with the mixture into a strong magnetic 

 field ; the latter mode has the advantage of enabling 

 us to watch the changes in the distribution of the 

 lines under changing conditions or continued strain." 

 From this we gather that there are at the very 

 least strong features of resemblance between the 

 remarkable dance of the chromosomes and opera- 

 tions which can be produced by means of purely 

 physical conditions, but does this mean that the 

 two are really identical or even similar processes ? 

 Similar, but not identical, is Professor Hartog's 

 reply to this question. "Though," he says, "the 

 forces at work in the dividing cell are similar in 

 their effects to such physical forces as magnetism, 

 static electricity, and even capillarity, and models 

 utilising such physical forces have been devised to 

 1 Op. cit., p. 26, for references, etc., see his paper, Proc. 

 Roy. Soc. t 1905, B. Ixxvi., p. 548. 



