66 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



spermatozoon. This idea proved to be correct. I had just 

 previously found different esters to be especially active in helio- 

 tropic experiments, and now I tried the effect of ethyl acetate 

 upon the unfertilized eggs of S. purpuratus. 



1. It turned out that if these eggs are placed in sea-water 

 to which a little ethyl acetate has been added, they form a 

 typical fertilization membrane and begin to divide when 

 replaced in normal sea-water. As long as the eggs were left 

 in the sea-water that contained ethyl acetate, they formed no 

 membrane; further, they lost the power to form a membrane 

 if they remained too long in such sea-water. However, they 

 did form a membrane if they were exposed to the ethyl acetate 

 in sea-water for not more than a couple of minutes and were 

 then replaced in normal sea-water. Eggs treated in this manner 

 all formed a perfectly normal nuclear spindle after an hour, 

 and began to divide. As a rule they did not develop into 

 larvae; on the contrary, the eggs went to pieces in less than 

 twenty-four hours (at about 19 C.) without reaching the 

 blastula stage. But the following result was extremely sur- 

 prising. If the eggs of Strongylocentrotus were exposed for two 

 hours to hypertonic sea-water, often only a fraction of 1 per 

 cent of the eggs began to segment. If, however, a part of these 

 eggs were subsequently treated with ethyl acetate long enough 

 to cause the formation of a membrane upon transference 

 to normal sea-water, the majority of the eggs developed and 

 many in quite a normal manner. In the latter case segmenta- 

 tion followed its normal course and at normal speed, and some 

 of the larvae probably those arising from normally segmented 

 eggs rose to the surface of the water. Here then we had a 

 much more precise imitation of the process of fertilization. 1 



2. The next step was to determine whether this depended 

 upon a specific action of the ester or of one of its hydrolytic 



1 Loeb, "On an Improved Method of Artificial Parthenogenesis," University 

 of California Publications, Physiology, II, 83, 1905. 



