186 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



cytolysis. Can it be possible that the lower fatty acids are 

 only soluble in the cortical layer of the unfertilized egg while 

 the higher fatty acids are soluble in the whole egg and hence 

 cause cytolysis ? 



8. During experiments (which will be discussed later in 

 this book) on the sensitizing effect of SrCl 2 and BaCl 2 upon the 

 eggs of the sea-urchin, the writer found that unfertilized eggs 

 of S. purpuratus and franciscanus when left in isotonic (3/8 m) 

 solutions of SrCl 2 or BaCl 2 would sooner or later form typical 

 fertilization membranes. The time required for this effect 

 varied considerably for the eggs of various females. In some 

 cases eggs would form membranes in ten minutes, in other 

 cases just as many hours were required. When such eggs 

 were left to themselves, they disintegrated like the eggs in 

 which membrane formation was produced by butyric acid. 

 When afterward treated with a hypertonic solution for a short 

 time the eggs would develop into larvae. 1 



The writer tried vainly to produce similar effects by the 

 pure salts of NaCl, Na 2 S0 4 or sodium oxalate, and many other 

 salts. The unfertilized eggs of S. purpuratus will live in an 

 m/2 NaCl solution for several days without suffering any injury 

 and the same was found true for solutions of CaCl 2 . When 

 treated with sperm the eggs could be fertilized and they would 

 develop normally. 



This resistance of the eggs of purpuratus to isotonic sodium 

 salts is, however, quite extraordinary. It does not exist in the 

 egg of Arbacia. In these eggs, R. Lillie 2 succeeded in calling 

 forth membrane formation by putting them for five or ten 

 minutes into pure solutions of Nal or KI or NaCNS and KCNS, 

 and then transferring them to sea-water. " A large proportion, 

 in favorable experiments practically all, form fertilization mem- 

 branes, usually thin and close to the egg surface." These eggs 



1 Loeb, Archiv f. Entwicklungsmechanik, XXX, 44, 1910. 



2 R. Lillie, "The Physiology of Cell Division," Jour. Morphol, XXII, 695, 

 1911. 



