THE PROCESS OF FERTILIZATION. 279 



showed, as a rule, the same outline as the egg had in the 

 morula stage. It was, moreover, a rare thing that the whole 

 mass of the egg developed into one blastula. The disconnec- 

 tion of the various cleavage cells led, as a rule, to the formation 

 of more than one embryo from one egg. The results were in 

 a certain way similar to those I had obtained when I caused the 

 fertilized eggs of sea urchins to burst. In such cases a part 

 of the protoplasm flowed out from the egg but was able to 

 develop. These extraovates had no membrane, and of course 

 showed some irregularity in their outlines, but the irregularity 

 in this case was far less than that observed in the unferti- 

 lized 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 alive 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 unfertilized eggs for 

 about two hours into a mixture of equal parts of - 2 ^- nMgCU 

 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 MgCl2. 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 (con- 

 siderably later than the fertilized eggs do). Thus I had suc- 

 ceeded 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. 



