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 th6 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.' 



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. 



