ARTIFICIAL PropvucTIoN oF NorMAL Larva 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, 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, 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 #,°n MgCl, 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 
blastulee and plutei which develop from fertilized and 
unfertilized eggs. The former rise to the surface, the latter 
swim at the bottom of thedish. If eggs be kept for two hours 
in the MgCl, solution and then fertilized with normal sperm, 
the blastule rise to the surface. If they be fertilized with 
sperm that had been in MgCl, 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, 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 2,2n MgCl, and sea-water developed 
parthenogenetically. 
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