IV] 



AND STRUCTURE OF THE CELL 



323 



Among other investigations all leading towards the same general 

 conclusion, namely that differences of electric potential play their 

 part in the phenomena of cell division, I would mention a note- 

 worthy 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 also that this 

 difference fluctuates, or actually reverses its direction, periodically, 

 at epochs coinciding with successive acts of segmentation or other 



Fig. 100. Final stage in the first seg- 

 mentation of the egg of Cerebra- 

 tidus. From Prenant, after Coe*. 



Fig. 101. Diagram of field of force 

 with two similar poles. 



important phases in the development of the' eggt; just as other 

 physical rhythms, for instance, in the production of COg , had already 

 been shewn to do. Hence we need not be surprised to find that th^ 

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



* On differences in electrical potential in developing eggs, Amer. Journ. Physiol. 

 XII, pp. 241-275, 1905. This paper contains an excellent summary, for the time 

 being, of physical theories of the segmentation of the cell. 



t Gray has demonstrated a temporary increase of electrical conductivity in 

 sea-urchin eggs during the process of fertilisation, and ascribes the changes in 

 resistance to polarisation of the surface: Electrical conductivity of echinoderm 

 eggs, etc., Phil. Trans. (B), ccvii, pp. 481-529, 1916. 



