Nature of Formative Stimulation 149 



this membrane is apparently preformed in the unfertihzed egg; 

 and if this be true the process of membrane formation must 

 consist in the lifting up of a preformed film from the underlying 

 cytoplasm through the entrance of sea-water between this fihn 

 and the cytoplasm. In this process the surface film undergoes 

 a change, since the spermatozoon can enter into the egg before 

 but not after the membrane formation. That merely a change 

 in the nature of the surface film prevents the entrance of a 

 spermatozoon into the egg after the membrane formation can 

 be proved by the fact that if we tear the membrane mechanically 

 a spermatozoon can penetrate into the egg. This proves that 

 the surface film, even if it is already preformed in the unferti- 

 lized egg, has different qualities or a different structure when it is 

 in close contact with the cytoplasm than when it is lifted off 

 from the cytoplasm by a layer of sea-water. 



We have assumed that the membrane formation is deter- 

 mined by the action of a lysin or cytolytic agency upon the 

 cortical layer of the egg, whereby a protein in this layer absorbs 

 sea-water, and is thereby dissolved. This assumption leads to 

 two consequences: first it must be possible to show that the 

 fertilization membrane is permeable for sea-water and crystal- 

 loid substances but impermeable for colloids. The correctness 

 of this view can be proved. If we add to the sea-water, con- 

 taining eggs with a fertilization membrane, a certain quantity 

 of dissolved white of egg, tannin, or blood serum, the membrane 

 collapses and closes tight around the cytoplasm. The reason 

 is that almost all the liquid which existed between the mem- 

 brane and the cytoplasm diffused into the surrounding sea- 

 water. If the eggs are brought back into normal sea-wat(T 

 (free from protein) it diffuses again into the space between 

 the membrane and the cytoplasm, and the fertilization mem- 

 brane resumes its former distance from the c>i:oplasin and 

 its round shape. The membrane is, therefore, impermeai)le 

 for the colloids dissolved in sea-water. 



