ARTIFICIAL PARTHENOGENESIS 191 



at the surface of the egg immediately after the 

 sperm has entered. Here we have ocular evidence 

 that fertilization effects a change in the surface layer 

 of the egg. 



It has been shown that after this membrane is formed, 

 the permeability of the egg to salts and other agents is 

 affected and that the processes of oxidation are greatly 

 accelerated. 



In other words, the interior of the unfertihzed egg is 

 separated by means of its membrane from many things 

 in the surrounding medium — oxygen and the salts in 

 sea-water, for example. The egg after fertilization 

 lives in a new world. 



These same changes are brought about by those 

 external agents that cause artificial parthenogenesis. 

 Loeb has shown by a thorough study of the conditions 

 that any substance that causes cytolysis (a typical form 

 of cell destruction) will induce parthenogenesis if ap- 

 plied to the surface of the egg only. 



Loeb has shown that development depends not 

 only on a change in the surface of the egg, but on other 

 changes also. Hence his most successful methods are 

 those in which two agents are applied successively 

 to the egg — one affects primarily the surface, the other 

 the interior of the egg. If, for example, the eggs are 

 placed in a solution of a fatty acid, the membrane is 

 produced. The egg is then removed to pure sea 

 water from which oxygen has been driven out and left 

 there for three hours. After its return to sea water it 

 will produce a normal embryo. 



If, instead of putting the egg into water without 

 oxygen, a hypertonic solution of salts is used (50 cc. 



