166 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



alone is not able to induce the (stunted) membrane formation 

 in the eggs, but the addition of alkali increases the membrane- 

 forming power. This can be proved by the fact that the ad- 

 dition of alkali to the hypertonic solution causes a rise in the 

 rate of the oxidations of almost the same order as the addition 

 of the same amount of base to an isotonic solution (Table 

 XXXIV). 



TABLE XXXIV 



It is obvious that the weak base alone raises the rate of 

 oxidations practically to the same height as the combination 

 of base and hypertonic sea-water. The whole rise was due in 

 both cases to the membrane-forming effect for which the weak 

 base was sufficient. 



In the case of a strong base, the result may be different, 

 since in purpuratus neither the base nor the hypertonic solu- 

 tion alone may cause membrane formation (or the change in 

 the cortical layer of the egg) necessary for development. The 

 following may serve as an example (Table XXXV). Duration 

 of experiment one and one-half hours; temperature 18 C. 



