252 THE EVOLUTION OF CONTINUITY 



of attraction acting on the nuclear chromatin. In other 

 words, it is suggested that we have in the spindle what 

 might be termed a " magnetic field," and in the achromatic 

 poles two magnetic points of " similar polarity." 



This can be made clearer by reference to the well-known 

 experiment of iron filings in a magnetic field (Figs. 86, 87, 

 88). Here the lines of magnetic force of a bar magnet 

 have been made evident by means of iron filings. 



If two bar magnets like the above be brought near each 

 other, so that the south pole of the one faces the north 

 pole of the other, the two will experience strong mutual 

 attraction, and the force lines will pass directly from the 

 north pole of the one to the south pole of the other. By 



Fig. 87. — Diagram of the lines of force between dissimilar 

 magnetic poles. 



means of iron filings this can be made evident, as in Fig. 87, 

 which shows the magnetic field between dissimilar poles. 



But if the north pole of one magnet be brought to face 

 the north pole of the other, there is no attraction, but 

 repulsion, and the magnetic field as made visible by iron 

 filings takes quite a different appearance (Fig. 88). 



Here the lines of magnetic force issuing from the poles 

 antagonise and repel each other. There is no passing across, 

 but where they meet a sharp angle is formed. The lines 

 do not he in one plane as the figure suggests, but radiate 

 in all directions from the poles. Thus, the diamond-shaped 

 space is really of cubic dimensions, being enclosed by a 

 false " spindle." 



In karyokinesis the achromatic nucleoli appear to act 



