298 ON THE INTERNAL FORM [ch 



outwards from the central "pole of concentration" along the lines 

 of diffusive force, and so mapping out for us a "monopolar field" 

 of diffusion : and if we set two such drops side by side, their fines 

 of diffusion will oppose and repel one another. Or, instead of the 

 uniform layer of salt solution, we may place at a little distance 

 from one another a grain of salt and a drop of blood, representing 

 two opposite poles: and so obtain a picture of a "bipolar field" 

 of diffusion. In either case, we obtain results closely analogous to 

 the morphological, but really dynamical, polarity of the organic 

 cell. But in all probability, the dynamical polarity or asymmetry 

 of the cell is a very complicated phenomenon: for the obvious 

 reason that, in any system, one asymmetry will tend to beget 

 another. A chemical asymmetry will induce an inequafity of 

 surface-tension, which will lead directly to a modification of form ; 

 the chemical asymmetry may in turn be due to a process of 

 electrolysis in a polarised electrical field; and again the chemical 

 heterogeneity may be intensified into a chemical polarity, by the 

 tendency of certain substances to seek a locus of gi^eater or less 

 surface-energy. We need not attempt to grapple with a subject so 

 compHcated, and leading to so many problems which lie beyond 

 the sphere of interest of the morphologist. But yet the morpho- 

 logist, in his study of the cell, cannot quite evade these important 

 issues; and we shall return to them again when we have dealt 

 somewhat with the form of the cell, and have taken account of 

 some of its simpler phenomena. 



We are now ready, and in some measure prepared, to study the 

 numerous and complex phenomena which accompany the division 

 of the cell, for instance of the fertilised egg. But it is no easy task 

 to epitomise the facts of the case, and none the easier that of late 

 new methods have shewn us new things, and have cast doubt on 

 not a little that we have been accustomed to believe. 



Division of the cell is of necessity accompanied, or preceded, by 

 a change from a radial or monopolar to a definitely bipolar sym- 

 metry. In the hitherto quiescent or apparently quiescent cell, we 

 perceive certain movements, which correspond precisely to what 

 must accompany and result from a polarisation of forces within: 

 of forces which, whatever be their specific nature, are at least 



