188 ON THE INTERNAL FORM AND [ch. 



Lillie comes easily to the conclusion that "electrical theories of 

 mitosis are entitled to more careful consideration than they have 

 hitherto received." 



Among other investigations, all leading towards the same 

 general conclusion, namely that differences of electric potential 

 play a great part in the phenomenon of cell division, I would 

 mention a very noteworthy paper by Ida H. Hyde*, in which the 

 writer shews (among other important observations) that not only 

 is there a measurable difference of potential between the animal 

 and vegetative poles of a fertilised egg {Fundulus, toad, turtle, 

 etc.), but that this difference is not constant, but fluctuates, or 

 actually reverses its direction, periodically, at epochs coinciding 

 with successive acts of segmentation or other important phases 

 in the development of the eggt; just as other physical rhythms, 

 for instance in the production of CO2, had already been shewm 

 to do. Hence we shall be by no means surprised to find that the 

 "materialised" lines of force, which in the earlier stages form the 

 convergent curves of the spindle, are replaced in the later phases 

 of caryokinesis by divergent curves, indicating that the two foci, 

 which are marked out within the field by the divided and recon- 

 stituted nuclei, are now alike in their polarity (Figs. 58, 59). 



It is certain, to my mind, that these observations of Miss 

 Hyde's, and of Lillie's, taken together with those of many writers 

 on the behaviour of colloid particles generally in their relation 

 to an electrical field, have a close bearing upon the physiological 

 side of our problem, the full discussion of which lies outside our 

 .present field. 



The break-up of the nucleus, already referred to and ascribed 

 to a diminution of its surface-tension, is accompanied by certain 

 diffusion phenomena which are sometimes visible to the eye ; and 

 we are reminded of Lord Kelvin's view that diffusion is implicitly 



* On Differences in Electrical Potential in Developing Eggs, Atner. Journ. of 

 Physiol, xn, pp. 241-275, 1905. This paper contains an excellent summary of 

 various physical theories of the segmentation of the cell. 



t Gray has recently demonstrated a temporary increase of electrical con- 

 ductivity in sea-urchin eggs during the process of fertihsation (The Electrical 

 Conductivity of fertilised and unfertiUsed Eggs, Journ. Mar. Biol. Assoc, x, pp. 

 50-59, 1913). 



