6 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



in sufficient concentration. If the oxygen is driven out of the 

 hypertonic solution, or if the oxidations in the egg are prevented 

 by the addition of some KCN to the sea-water, the develop- 

 mental effect of the hypertonic solution is lacking. 



Shortly after obtaining larvae from unfertilized sea-urchin 

 eggs by means of hypertonic sea-water, I was able to obtain 

 swimming larvae from the unfertilized eggs of Chaetopterus by 

 the use of potassium and acids, and of starfish eggs by means 

 of acids, without it being necessary to increase the osmotic 

 pressure of the sea-water. 



With these experiments one task was accomplished, namely, 

 the substitution of physicochemical agencies for the mysterious 

 complex "living spermatozoon." But these experiments did 

 not yet allow us to draw any conclusions concerning the 

 nature of the process of fertilization. 



4. Every biologist knew that the eggs of many marine ani- 

 mals underwent a characteristic change immediately after 

 the entrance of the spermatozoon, namely, the formation of the 

 so-called fertilization (vitelline) membrane. This phenomenon 

 was always considered to be something of very secondary 

 importance, and I therefore attached no significance to the 

 fact that after the osmotic treatment the egg formed no typical 

 fertilization membrane. However, in 1905 I discovered that a 

 short exposure of the sea-urchin egg to a monobasic fatty acid, or 

 to C0 2 , led to the formation of a typical fertilization membrane 

 by all the eggs of Strongylocentrotus purpuratus; and, moreover, 

 that all these eggs could be induced to develop into larvae after 

 artificial membrane formation by a subsequent short exposure, 

 some thirty to fifty minutes, to hypertonic sea-water. If mem- 

 brane formation alone is evoked, without subsequent exposure 

 of the eggs to hypertonic sea-water, they begin to segment, but 

 then disintegration sets in; and the higher the temperature, the 

 sooner does this disintegration make its appearance. If the 

 temperature is very low, the eggs can develop to early larval 



