THE PERMEABILITY OF THE EGG MEMBRANE. 381 



salts were most powerful in shortening the period of susceptibility 

 of the egg to its own sperm. 



Experiment I. Large numbers of eggs from various females 

 were stripped into distilled water, mixed thoroughly and trans- 

 ferred to dishes containing respectively 100 c.c. of 



A. T 5 5 n. CaCl 2 , C. ^ n. NaCl, 



B. t V . MgCl 2 , D. A . KC1. 



These solutions were made approximately isotonic with sea water 

 so as to eliminate the factor of osmosis, although, as stated, these 

 eggs are practically immune to osmotic changes. After periods 

 of five, ten, twenty and thirty minutes' exposure to these solu- 

 tions, successive lots of eggs averaging about fifty in number 

 were taken out, washed in sea water and an attempt made to fer- 

 tilize them in sea water. 



The results of this experiment follow : 



A. (y 5 n. CaCl 2 ). No eggs fertilized at all and all showed 

 coagulation of the blastodisc or plasmolysis of the entire proto- 

 plasmic mass, after an exposure of five minutes or longer. 



B. (^ H. MgCl 2 ). No eggs fertilized and all showed a vacu- 

 olated condition of the protoplasm and a considerable amount of 

 plasmolyses after exposures of five minutes or longer. 



C. ( T 6 Q n. NaCl). About 30 per cent, of all eggs fertilized and 

 cleaved normally and nearly all of these formed embryos, even 

 after the maximum exposure of thirty minutes. 



D. ( T c //. KC1). From 60 to 75 per cent, of eggs fertilized 

 and cleaved normally, producing normal embryos, even after the 

 maximum exposure of thirty minutes. 



From this experiment it will readily be seen that calcium 

 salts are the most active in preventing fertilization, while sodium, 

 and especially potassium salts, have relatively little inhibiting 

 effect. 



Experiment //. In order to test the relative toxicity of these 

 solutions before and after fertilization the following simple exper- 

 iment was undertaken : A large number of eggs were fertilized 

 in sea water, washed rapidly in distilled water and transferred to 

 the same solution used in Experiment I. After standing in 

 these solutions for thirty minutes they were returned to sea water 



