Artificial Parthenogenesis 101 



salts, e. g., BaCl 2 and SrCl 2 in the case of the egg of 

 purpuratus, and according to R. Lillie, Nal or NaCNS 

 in the egg of Arbacia. Whenever we submit an unfer- 

 tilized sea-urchin egg to any of these agencies and 

 restrict the cytolysis to the superficial or cortical layer 

 of the egg (i. e., if we transfer the egg to normal sea 

 water before the cytolytic agent has had time to diffuse 

 into the main egg) the egg will form a membrane and 

 behave as if the membrane formation had been called 

 forth by a fatty acid, with this difference only, that 

 the various agencies are not all equally harmless for the 

 egg. 1 



If the idea was correct that the change underlying 

 membrane formation was essentially a cytolysis of the 

 cortical layer of the egg, it was to be expected (from the 

 data contained in Chapter III) that the blood serum 

 or the cell extracts of foreign species would also cause 

 membrane formation and thus induce the development 

 of the unfertilized egg, while serum of animals of the 

 same species or genus would have no such effects. This 

 was found to be correct. In 1907 the writer showed 

 that the blood serum of a Gephyrean worm, Dendro- 

 stoma, was able to cause membrane formation in the 

 egg of the sea urchin. When added in a dilution of 

 I c.c. of serum to 500 or 1000 c.c. of sea water to eggs of 

 purpuratus a certain number formed fertilization mem- 

 branes. It was found later that the serum and tissue 



1 The reader is referred for details to the writer's book on the subject. 



