178 Artificial Parthenogenesis and Fertilization 



bile salts to normal sea-water, they did not develop if left 

 therein. But some of them did develop into larvae after a 

 subsequent short exposure to a hypertonic solution. The 

 eggs were more harmed by membrane formation with bile salts 

 than by membrane formation with saponin. 



In both cases only those eggs developed, after a short treat- 

 ment with hypertonic sea-water, which had formed membranes, 

 a fact which is also true of eggs treated with a fatty acid.^ 



3. In 1905 I started experiments on membrane formation in 

 the egg by means of soaps; but by chance these experiments 

 led to no results. The experiments were resumed a few years 

 later with positive results. For since soaps are good cytolytic 

 agents, one could postulate a definite result from these experi- 

 ments. I will first briefiy portray the cytolytic effect of the 

 soaps and then discuss their developmental effect. 



As soap is precipitated by calcium, it was necessary to 

 dissolve it in m/2 NaCl solution, instead of in sea-water. Now 

 when the unfertilized eggs of S. purpuratus (after being freed 

 from sea-water by washing in m/2 NaCl) are placed in 50 c.c. 

 of neutral m/2 NaCl-|-2 c.c. m/10 sodium oleate, neither mem- 

 brane formation nor cytolysis occurs as a rule in that solution. 

 The eggs only become angular. But if they are placed after a 

 few minutes in sea-water, a large number of them form mem- 

 branes at once, which in a few eggs is followed by cytolysis. 

 The longer the eggs remain in the soap solution, the greater 

 becomes the percentage forming membranes and cytolyzing 

 after transference to ordinary sea-water. For the eggs of many 

 sea-urchins the addition of 2 c.c. of sodium oleate to 50 c.c. of 

 NaCl is too little, and about 3 c.c. of soap must be added. 



Why does the soap solution not cause membrane formation 

 until after the egg has been replaced in sea-water ? The reason 

 is that it is the sea-water which causes the membrane forma- 

 tion as a result of its alkaline reaction. The soap solution either 



^ Loeb, op, cii. 



