Nature of Formative Stimulation 145 



possess a greater tendency to develop spontaneously, it might 

 also be found that the number of eggs developing spontaneously 

 might be increased by agitation. 



I tried whether it is possible to cause the eggs to cytolyze 

 also mechanically. If we exercise only a slight pressure with 

 a finger upon the ovary of a star-fish we find that many of 

 the eggs which afterward leave the ovary are cytolyzed. This 

 cytolysis is not caused by a bursting of the egg membrane; on 

 the contrary, in this case the cytolysis of the egg is, as usual, 

 preceded by the formation of a membrane of fertilization and 

 this membrane remains intact in the star-fish egg which is 

 caused to cytolyze by mechanical pressure. In the sea-urchin 

 egg, however, it is impossible to produce cytolysis by a slight 

 pressure. 



The eggs of the star-fish which develop spontaneously first 

 form a membrane. Shaking causes a development of the star- 

 fish eggs only if the shaking first leads to a membrane formation. 

 The greater tendency of the star-fish to develop spontaneously 

 is, therefore, due to the greater ease with which cytolysis can 

 be produced in this egg. 



How can mere agitation or pressure call forth membrane 

 formation or cytolysis ? It seems to me that this fact is most 

 easily understood under the assumption, first suggested b\' 

 Biitschli, that the cytoplasm is an emulsion. It would then 

 follow that the membrane formation as well as the c>i:olysis 

 depends upon the destruction of this emulsion. We know that 

 different emulsions have a different degree of durability. The 

 eggs which upon gentle pressure undergo cytolysis have an 

 emulsion with a lesser degree of durability than the eggs in which 

 pressure has no such effect. Let us assume that membrane 

 formation as well as cytolysis depends upon the destruction 

 of an emulsion; in this case the membrane formation de])ends 

 upon the destruction of the emulsion in the cortical layer of the 

 egg only. The lysin of the egg destroj's only the emulsion in 



