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, and BaCl, 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, or BaCl, 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." 
The writer tried vainly to produce similar effects by the 
pure salts of NaCl, Na,SO, 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, 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? succeeded in calling 
forth membrane formation by putting them for five or ten 
minutes into pure solutions of NaI 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. 
2R. Lillie, ‘‘The Physiology of Cell Division,’’ Jour. Morphol., XXII, 695, 
1911. 
