OF VITAL PHENOMENA 159 



tion membrane, appears between the jelly and the egg. Both 

 of these might vitiate the conductivity experiments. It was found 

 that if the jelly is washed from the eggs before they are fertilized, 

 no fertilization membranes appear. 



The eggs from which the jelly was washed (with sea water) 

 were placed in the conductivity cell and gently centrifuged. The 

 level to which the eggs came was marked on the cell and the 

 conductivity determined by the Kohlrausch method. The eggs 

 were then transferred to a large quantity of sea water with just 

 enough sperm to fertilize all or at least 80 per cent of the eggs, 

 then washed in fresh sea water and returned to the cell. The eggs 

 were centrifuged down to the same level as before fertilization 

 and the conductivity again determined, which was found to be 

 greatly increased. This experiment was repeated many times 

 with the same result. It was also confirmed by J. Gray (1913 a, 

 b) who observed that about fifteen minutes after fertilization the 

 conductivity began to fall again. 



Since the spaces between the eggs were the same during the 

 two determinations and were filled with sea water having the 

 same conductivity in each determination, the change in conduc- 

 tivity is evidently due to the change in permeability of the eggs 

 to ions. 



This increase in permeability should decrease the polarization 

 and increase the surface tension, supported by the fact that the 

 eggs round up. The division of the eggs must be due to local 

 changes in surface tension, and is therefore not the direct result 

 of the initial permeability change, but probably an indirect re- 

 sult of it. 



After the general increase in permeability, the original semi- 

 permeability is partially regained. It is only necessary to assume 

 that the semipermeability is regained first at the poles, thus leav- 

 ing the equator with the greatest surface tension, in order to 

 account for the division'. 



The increase in permeability of the egg on fertilization was 

 demonstrated in other ways. It was -found that fertilized Ar- 

 bacia eggs are more easily plasmolyzed by cane sugar solution 

 than are unfertilized eggs, indicating permeability of the fer- 

 tilized eggs to ions. This may be due, however, to increased 

 permeability to water, observed by Lillie (1916 a). 



