186 



ON THE INTERNAL FORM AND 



[CH. 



is drawn in opposite directions by equal forces, and so tends to 

 remain undisturbed, in the form of an "equatorial plate." 



Nor should we omit to take account (however briefly and 

 inadequately) of a novel and elegant hypothesis put forward by 

 A. B. Lamb. This hypothesis makes use of a theorem of Bjerknes, 

 to the effect that synchronously vibrating or pulsating bodies in 

 a hquid field attract or repel one another according as their 

 oscillations are identical or opposite in phase. Under such 

 circumstances, true currents, or hydrodynamic lines of force, are 

 produced, identical in form with the hues of force of a magnetic 

 field ; and other particles floating, though not necessarily pulsating, 

 in the hquid field, tend to be attracted or repelled by the pulsating 



Fig. 57. Artificial caryokinesis (after Leduc), for comparison 

 with Fig. 41, p. 169. 



bodies according as they are lighter or heavier than the surrounding 

 fluid. Moreover (and this is the most remarkable point of all), 

 the fines of force set up by the oppositely pulsating bodies are the 

 same as those which are produced by opposite magnetic poles : 

 though in the former case repulsion, and in the latter case attrac- 

 tion, takes place between the two poles*. 



But to return to our general discussion. 



While it can scarcely be too often repeated that our enquiry 

 is not directed towards the solution of physiological problems, save 



* Lamb, A. B., A new Explanation of the Mechanism of Mitosis, Journ. Exp. 

 Zool. y, pp. 27-33, 1908. 



