58 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



4 replaced in normal sea-water they developed into swimming 

 plutei. 1 I expected that the same result would also be obtained 

 with NaCl, KC1, and CaCl 2 , 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. Then, 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 2 , 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 



1 In the previously quoted detailed account of this first investigation (1900) 

 I expressly mentioned that the raising of the osmotic pressure of the solution was 

 a necessary condition of the experiment. 



