120 The Mechanistic Conception of Life 



was far less than that observed in the unfertilized eggs of my 

 recent experiments. But although I had thus far satisfied my 

 desire to see the unfertilized eggs of the sea-urchin reach the 

 blastula stage, I was not able to keep these eggs ahve long 

 enough to see them grow into the pluteus stage. They developed 

 more slowly than the normal eggs, and died, as a rule, on the 

 second day. 



It was my next task to find a solution which would allow 

 the eggs to reach the pluteus stage. I found that this can be 

 done by reducing the amount of magnesium chloride and 

 increasing the amount of sea-water. By putting the unferti- 

 lized eggs for about two hours into a mixture of equal parts of 

 \"-n MgClg and sea-water, the eggs, after they were put back 

 into normal sea-water, not only reached the blastula stage, but 

 went into the gastrula and pluteus stages. The blastulae that 

 originated from these eggs looked much healthier and more 

 normal than those of the former solution with more MgCla. 

 Of course as these unfertilized eggs had no membrane it 

 happened but rarely that the whole mass of an egg developed 

 into one single embryo. Quadruplets, triplets, and twins were 

 much more frequently produced than a single embryo. The 

 outlines of each blastula were much more spherical than in the 

 previous experiment. These eggs reached the pluteus stage on 

 the second day (considerably later than the fertilized eggs do). 

 Thus I had succeeded in raising the unfertilized eggs of sea- 

 urchins to the same stage to which the fertilized eggs can be 

 raised in the aquarium. I have not yet succeeded in raising the 

 fertilized eggs in my laboratory dishes beyond the pluteus stage. 



Though I do not wish to go into the technicalities of these 

 experiments, I must mention a few of the precautions that I 

 took in order to guard against the possible presence of sperma- 

 tozoa in the sea-water.^ The reader who is interested in this 



1 Today it may seem strange that I had to meet such objections, but when my 

 first papers on artificial parthenogenesis appeared, very few biologists were willing 

 to accept the correctness of my statements. The most absurd soiu"ces of error 

 were suggested. 



