INITIATION OF DEVELOPMENT IN EGG OF ARBACIA. 395 



If we define cytolysis as a breaking up of the cell within the mem- 

 brane or actual liberation of the cell contents, we may define 

 plasmolysis as a shrinkage of the cell contents. Now, certainly 

 hypertonic sea-water as employed in these experiments never 

 caused any liberation of the cell contents. We can not, therefore, 

 regard the action of hypertonic sea-water as cytolytic. 



There is another way of reaching a conclusion in this matter. 

 Prolonged exposure to butyric acid in sea-water will cause the 

 uninseminated egg of Arbacia on return to normal sea-water to 

 form a fine gelatinous film instead of a membrane. Such eggs, 

 as Loeb noted, soon cytolyze. We may accept this specific in- 

 stance as a definition. Now, such eggs go to pieces by droplet 

 formation ; thus they disintegrate. Or, if eggs with membranes 

 induced by exposure to butyric acid are allowed to lie in normal 

 sea-water, they eventually disintegrate by the formation of globules 

 in the cortex. The disintegration eventually involves the whole 



egg- 



In hypotonic sea- water both Arbacia and Echinarachnius eggs 

 take up water, lose pigment, and assume a granular appearance. 

 The contents then slowly disappear as if washed away. Rarely 

 do the contents of the eggs burst through the membrane before 

 total disintegration. 



Now, the effect of hypertonic sea-water on these eggs is unlike 

 that of butyric acid or hypotonic sea-water. Rather the effect of 

 hypertonic sea-water is plasmolytic. In it the egg shrinks, be- 

 comes darker. On return to normal sea- water such an egg, if it 

 fail to develop, remains intact for hours. 



Unless, therefore, we change the meaning of the term cytolysis, 

 the hypertonic sea-water employed in these experiments is not 

 cytolytic. Instead of disintegrating, the eggs on return to normal 

 sea-water cleave, gastrulate, and reach the pluteus stage. 



3. If we admit that hypertonic sea-water does not call forth 

 membranes by superficial cytolysis, then we must conclude that 

 the hypothesis of a superficial cytolysis as part of the mechanism 

 of experimental parthenogenesis is as unnecessary for a theory of 

 experimental parthenogenesis as it is superficial and inadequate for 

 a theory of fertilization. This must follow for several reasons. 



First, we well know from older work that hypertonic sea-water 



