THE PHYSIOLOGY OF CELL DIVISION 47 



5. The view is put forward that the essential physiological 

 effects produced by the two successive treatments in artificial 

 parthenogenesis are opposite in character and correspond re- 

 spectively to the depolarizing and the repolarizing phases of the 

 stimulation-process in irritable tissues in general. The primary 

 or membrane-forming treatment has a permeability-increasing 

 and hence depolarizing effect upon the plasma membrane. This 

 initial depolarization is probably the critical or determinative 

 event in fertilization, as well as in stimulation. A return of the 

 plasma membrane to or toward the original semi-permeable and 

 electrically polarized condition within a certain time {ca. fifteen 

 minutes at 20°), is, however, essential if normal development is 

 to follow, otherwise cytolysis results. This recovery of the normal 

 semi-permeability of the membrane, with the correlative elec- 

 trical polarization, is favored by after-treatment with agencies 

 (cold, cyanide, anesthetics, hypertonic sea-water) whose general 

 action is permeability-decreasing or anti-cytolytic. Hence, such 

 after-treatment increases the proportion of eggs that regain their 

 normal properties and continue development. 



