68 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



eggs of the same female developed when treated with hyper- 

 tonic sea-water alone. 1 



3. The next question which arose was whether the fatty 

 acid starts the development directly, or whether its action is 

 only limited to the setting-off of the process of membrane 

 formation; in that event, this process, formerly regarded as 

 something very secondary, would be established as the essential 

 factor in development. The question was answered in the 

 latter sense, as the following facts show. If the unfertilized 

 eggs of the sea-urchin S. purpuratus are placed for one and one- 

 half to two and one-half minutes at 15 C. in 50 c.c. of sea-water 

 +2.8 c.c. of a N/10 monobasic fatty acid, all the eggs form 

 a membrane upon transference to ordinary sea-water. This 

 result is so constant that I have only rarely found an 

 exception to it. But if the eggs are removed a little earlier from 

 the acid to normal sea-water, one can find a period of time in 

 which no longer all the eggs but only some of them form 

 membranes. It will be found that only such eggs as have 

 formed membranes develop, if they are subsequently or 

 previously treated with hypertonic sea-water. 2 Membrane 

 formation is therefore the deciding condition for development. 



A further proof is afforded by the following fact. We shall 

 see in the following chapters that any substance which causes 

 haemolysis also calls forth membrane formation, e.g., saponin, 

 bile salts, hydrocarbons, ether, etc. No matter by what 

 means the membrane formation has been called forth, it induces 

 the development of the egg, provided that the eggs are taken out 

 of these solutions at the proper time. If such eggs which 

 possess a membrane are afterward subjected to treatment 

 with hypertonic sea-water they develop like fertilized eggs. 



1 Loeb, "On an Improved Method of Artificial Parthenogenesis," 2d and 3d 

 communications, University of California Publications, Physiology, II, 1905; Un- 

 tersuchungen zur kunstlichen Parthenogenese, pp. 322 and 329, Leipzig, 1906. 



2 The beginner must bear in mind that the membrane occasionally adheres 

 closely to the egg and that occasionally the process of membrane formation is not 

 completed. However, such eggs can develop. 



