SECT. 5] IN ONTOGENESIS 833 



a very unpromising line of research, for, to begin with, it will always 

 be a matter of extreme difficulty to hit on the right strength of current 

 or of magnetic field to influence the embryonic processes without 

 causing pathological states to arise. It is interesting, however, that 

 Brown found that the eggs of Fundulus were as immune to electrical 

 stimulation as to other influences, such as osmotic pressure. 



Among the various electrical properties of eggs and embryos which 

 are to be discussed in this section the charge on the egg has so far 

 not been mentioned. Cataphoresis experiments with echinoderm 

 eggs were made by McClendon in 19 14, who found that, when the 

 jelly had been removed from them, they were transported to the 

 anode, and possessed therefore a negative charge. The surrounding 

 jelly, however, went the other way, and had a positive charge; thus 

 McClendon suggested that the fertilisation membrane might be the 

 result of mutual precipitation by antagonistically charged colloids. 

 Tomita, again, working with nematode eggs [Ascaris, Oxyuris, Anky- 

 lostomum), trematode eggs {Distoma) and cestode eggs {Taenia and 

 Bothriocephalus) , found in all cases a migration from cathode to anode, 

 and so a negative charge. Szent-Gyorgyi, however, found no cata- 

 phoretic movement at all in the case of Labrus rupestris and Echinus 

 vulgaris eggs. Vies & Nouel, who made some experiments involving 

 the degree of agglutination of echinoderm eggs at different j&H, agreed 

 with the conclusions of McClendon, although experimentally their 

 Strongplocentrotus eggs moved towards the cathode. In view of the 

 fact that three different workers have obtained the three possible 

 results on this material, it is clear that further observations are to be 

 desired. Vies, Achard & Prikelmaier, working on the pounded and 

 cytolysed protoplasm of Strongylocentrotus eggs, found cataphoresis 

 towards the cathode below />H 5-8 and towards the anode above it, 

 from which they concluded, as has already been mentioned, that the 

 iso-electric point of the egg-proteins was about 5-5. 



5-9. Refractive Index, Surface Tension and Viscosity 



Vies has studied a number of the biophysical properties of the sea- 

 urchin's egg, such as refractive index. He regarded the refringent 

 spherical or ellipsoidal ^gg as a lens, from which the refractive index 

 could be calculated, knowing the focal distance. The necessary 

 measurements were (i) the curvature of the egg, ascertained by 

 micrometric measurements along different diameters, (2) the focal 



