294 ON THE INTERNAL FORM [ch. 



cell. For indeed, just as uniform expansion about a single centre, 

 to whatsoever physical cause it may be due, will lead to the con- 

 figuration of a sphere, so will any two centres or foci of potential 

 (of whatsoever kind) lead to the configurations with which Faraday 

 first made us famihar under the name of "lines of force*"; a^d 

 this is as much as to say that the phenomenon, though physical in the 

 concrete, is in the abstract purely mathematical, and in its very essence 

 is neither more nor less than a property of three-dimensional space. 



But as a matter of fact, in this instance, that is to say in trying 

 to explain the leading phenomena of the caryokinetic division of 

 the cell, we shall soon perceive that any explanation which is based, 

 like Rhumbler's, on mere mechanical traction, is obviously inade- 

 quate, and we shall find ourselves limited to the hypothesis of some 

 polarised and polarising force, such as we deal with, for instance, 

 in magnetism or electricity, or in certain less familiar phenomena 

 of hydrodynamics. Let us speak first of the cell itself, as it appears 

 in a state of rest, and let us proceed afterwards to study the more 

 active phenomena which accompany its division. 



Our typical cell is a spherical body; that is to say, the uniform 

 surface-tension at its boundary is balanced by the outward resistance 

 of uniform forces within. But at times the surface-tension may be 

 a fluctuating quantity, as when it produces the rhythmical con- 

 tractions or "Ransom's waves "f on the surface of a trout's egg; or 

 again, the surface-tension may be locally unequal and variable, giving 

 rise to an amoeboid figure, as in the egg of HydraX- 



Within the cell is a nucleus or germinal vesicle, also spherical, 



* The configurations, as obtained by the usual experimental methods, were 

 of course known long before Faraday's day, and constituted the "convergent and 

 divergent magnetic curves" of eighteenth century mathematicians. As Leslie 

 said, in 1821, they were "regarded with wonder by a certain class of dreaming 

 philosophers, whp did not hesitate to consider them as the actual traces of an 

 invisible fluid, perpetually circulating between the poles of the magnet." Faraday's 

 great advance was to interpret them as indications of stress in a medium — of. 

 tension or attraction along the lines, and of repulsion transverse to the lines, of the 

 diagram. 



t W. H. Ransom, On the ovum of osseous fishes, Phil. Trans, clvii, pp. 431-502, 

 1867 (vide p. 463 et. seq.) (Ransom, afterwards a Nottingham physician, was 

 Huxley's friend and class-fellow at University College, and beat him for the medal 

 in Grant's class of zoology.) 



X Cf, also the curiou.s phenomenon in a dividing egg described as "spinning" 

 by Mrs G. F. Andrews, Journ. Morph. xii, pp. 367-389, 1897. 



