68 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
eggs of the same female developed when treated with hyper- | 
tonic sea-water alone.! 
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. of a N/i0 monobasic fatty acid, all the eggs form 
& 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 eges which 
possess a membrane are afterward subjected to treatment 
with hypertonic sea-water they develop like fertilized eggs. 
‘ Loeb, ‘‘On an Improved Method of Artificial Parthenogenesis,’’ 2d and 3d 
communications, University of California Publications, Physiology, If, 1905; Un- 
tersuchungen zur kiinstlichen Parthenogenese, pp. 322 and 329, Leipzig, 1906. 
?'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. 
