58 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 
replaced in normal sea-water they developed into swimming 
plutei.’ I expected that the same result would also be obtained 
with NaCl, KCl, and CaCl,, but to my surprise this was not the 
case. Meanwhile since the spawning season had expired, and 
there were less than a dozen sea-urchins at my disposal, I used 
this material to confirm at least the main and most important 
result, that it is really possible to produce larvae from unferti- 
lized sea-urchin eggs. Eight series of experiments, each with a 
large number of different solutions, which I was still able to 
carry out together with many control experiments, convinced 
me that I had succeeded in the artificial production of larvae 
from unfertilized eggs. Not only blastulae but also gastrulae 
and plutei, some of them entirely normal in appearance, had been 
produced. “When, however, the further question arose whether 
this was an effect of the hypertonic sea-water alone or whether 
a specific action of magnesium was responsible for the result.| 
Lack of material made it impossible for me to decide this 
question the same summer at Woods Hole. In February, 1900, 
I took up this investigation at Pacific Grove on the California 
coast. Dr. Garrey, my assistant at that time, accompanied 
me; ‘and we were able to prove that an increase of concentration 
of sea-water, not only by MgCl, but also by NaCl and sugar, 
incited the development of the sea-urchins of that coast— 
Strongylocentrotus purpuratus and franciscanus.} We made sure 
also of the fact that the most scrupulous sterilization of the sea- 
water and of the instruments and the elimination of all possible 
sources of error did not invalidate the results. However, besides 
these gratifying results we also had a very unwelcome experience 
which long remained inexplicable to me: The results in Pacific 
Grove were not so constant as in Woods Hole. On some days 
the experiments went very well, but then there followed days on 
which the same solution which had hitherto given good results 
i1In the previously quoted detailed account of this first investigation (1900) 
I expressly mentioned that the raising of the osmotic pressure of the solution was 
@ necessary condition of the experiment. 
