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 
eges—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. 
