ARTIFICIAL PrRropucTIon oF NoRMAL Larvs#® 615 
(1) 50 c.c. 4’n MgCl. +50 c.c. sea-water 
(2) Normal sea-water 
Two hours later the eggs from solution 1 were put back 
into normal sea-water. Three and a half hours later about 
50 per cent. of the eggs that had been in solution 1 were 
divided into from 2 to 16 cells, but not an egg had a mem- 
brane. The control eggs that had been in normal sea-water 
all the time were all without membrane and absolutely unseg- 
mented. Millions of eggs were examined under the micro- 
scope. The next morning the eggs that had been in solution 
1 had reached the blastula stage and were swimming about. 
A small number were in a gastrula stage and even beginning 
to assume a pyramidal form. In the control eggs not one 
had developed. Perhaps one in a hundred had amceboid 
forms such as precede segmentation in unfertilized eggs, but 
not an egg was segmented, and not one had a membrane. 
The next day some of the blastule of the other lot had 
reached the pluteus stage. The control experiments will be 
discussed in the next paragraph. 
Possible sources of error and objections.—F rom all these 
experiments I draw the conclusion that by putting the unfer- 
tilized eggs of Arbacia for two hours into a solution of 60 c.c. 
20 n MgCl, + 40 c.c. sea-water the eggs develop into blastule 
if brought back into normal sea-water. If we put the unfer- 
tilized eggs for about two hours into a solution of equal parts 
of 2.n MgCl, and sea-water, the eggs may reach the pluteus 
stage. The possible objection might be that the eggs were 
fertilized. Such fertilization could only have been caused 
by the instruments or hands of the experimenter having 
been in contact with spermatozoa, or by the sea-water con- 
taining spermatozoa. The first possibility was absolutely 
excluded through the above mentioned precautions. The 
second possibility was rendered practically impossible, as, 
first, the spawning season was practically over, and, second, 
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