Prevention of Death by Fertilization 159 



The first of these substances causes the formation of a mem- 

 brane; the second serves the purpose of rendering the egg 

 immune against the fatal action of oxidations. 



I have sho^vn in a number of papers that the essential 

 feature in the causation of the development of the egg is a 



Fig. 48 



Fig. 49 



Fig. 50 



Figs. 48-50. — Disintegration of the sea-urchin egg after the membrane for- 

 mation with butyric acid or with foreign serum or with the extract of sperm or of 

 foreign cells; if the eggs are not treated after the membrane formation with a 

 hypertonic solution or a suppression of oxidations. A indicates the area where 

 the disintegration begins. 



modification of its surface, which in many cases leads to the 

 formation of a membrane. If we cause membrane formation in 

 an unfertilized sea-urchin egg by artificial means, it begins to 

 develop, but very soon perishes; much more rapidly than 

 if it is not exposed to any treatment. I was able to show that 



