ARTIFICIAL PRODUCTION OF NORMAL LARV.E 619 



and within another minute all the eggs were fertilized. At 8:52 

 another test was made, but at this time the egg membrane did not 

 appear, showing that fertilization did not take place. At 9 o'clock 

 about one egg in every 100 was fertilized. 



Norman repeated these experiments several times with the 

 same result. They prove that even a small addition of 

 MgCl 2 to sea- water, much smaller than in any of our 

 experiments, suffices to annihilate the power of impregnation 

 in the spermatozoa in a very short time. In my own experi- 

 ments the increase in the osmotic pressure of the sea-water 

 was much greater than in Norman's experiments. I made 

 another control experiment in the ninth series which bears 

 on the same question. Unfertilized eggs were left in a 

 solution of equal parts of 2 -/ n MgCl 3 and sea- water for two 

 hours. At the end of that time they were put back into 

 normal sea-water to which sperm was added which had also 

 been in a solution of equal parts of y n MgCl 2 and sea- 

 water for two hours. Only very few of the eggs formed a 

 membrane. 



There is, as we saw, a typical difference between the 

 blastula3 and plutei which develop from fertilized and 

 unfertilized eggs. The former rise to the surface, the latter 

 swim at the bottom of the dish. If eggs be kept for two hours 

 in the MgCl 2 solution and then fertilized with normal sperm, 

 the blastulae rise to the surface. If they be fertilized with 

 sperm that had been in MgCl 3 solution for two hours, they 

 remain at the bottom of the dish like the unfertilized eggs. 

 It is thus clear, I think, that even this last possible objection 

 that the treatment with the MgCl 2 solution increases the 

 impregnating power of the spermatozoa, or the impregna- 

 bility of the egg must be discarded. Hence I draw the 

 conclusion that the unfertilized eggs that had been treated 

 with equal parts of a / n MgCl 2 and sea-water developed 

 parthenogenetically. 



