44 CLEAVAGE II 



-presumed to be permeable to water and salts, but imperme- 

 able to the proteins and sugars in the egg sea-water is then 

 absorbed and the membrane raised from the surface. 



There are facts which support this view. In the first 

 place it is known that all haemolytic agents all agents that 

 cause the diffusion of haemoglobin from a blood corpuscle- 

 are also capable of inciting the formation of the membrane in 

 these ova. Such are electricity, heat, hydroxyl ions, hydrogen 

 ions, distilled water, fat solvents, bile-salts, soaps, glucosides, 

 such as saponin, digitalin, solanin, and blood- sera. Haemolysis 

 must depend on an alteration of the permeability of the 

 surface-layer. 



In the second place Lillie has shown that the order of 

 effectiveness of neutral salts of potassium and sodium in 

 causing membrane formation is the same as the order of their 

 effectiveness in causing the liberation of the red pigment 

 from the egg of the Sea-urchin Arbacia, and the latter must 

 depend on an increased permeability of the peripheral layer 

 of the egg. 



The following table gives the salts in the order of effective- 



ness: 



COOCH 3 is least effective 



Cl 

 Br 



C10 



I 



CNS is most effective. 



The hypothesis seems peculiarly applicable to Nereis, for 

 here, as we have already seen, there is a preformed membrane 

 which becomes separated from the egg by a perivitelline fluid 

 as the result of insemination. This fluid is simply sea-water 

 which passes through the membrane and fills the superficial 

 alveoli from which their gelatinous contents have escaped 

 and diffused out. It will be noted that the membrane 

 must have become more permeable, and that the walls of the 

 alveoli remain, whereas on the lipoid-solution theory they 

 should disappear. 



