626 STUDIES IN GENEBAL PHYSIOLOGY 
searching the control material for segmented eggs, but were 
never able to find a single one. 
In addition to these control experiments we made several 
others. It was necessary to apply the mixture of equal parts 
of the 22» MgCl, solution and sea-water for from one to 
two hours to bring about the development of the unfertilized 
eggs. We made it a rule to take out one portion of eggs 
from this solution much earlier —in some cases after ten min- 
utes. In no case did one of these eggs segment or develop. 
A third series of control experiments was applied. Solu- 
tions with less MgCl, and more sea-water were tried. In 
solutions of 30 c.c. 2,°n MgCl,, and 70 c.c. sea-water not an 
egg was able to develop. 
If the first animal opened in these experiments happened 
to be a male, the instruments were at once laid aside for 
disinfection, and the next animal was opened by another 
experimenter with the same precautions. 
In some experiments we used sea-water that had been 
filtered through a new Pasteur filter. Although no sperma- 
tozoa are able to pass through such a filter, the eggs treated 
with a mixture of equal parts of a %,9n MgCl, solution and 
filtered sea-water developed, while none of the control eggs 
were able to develop. 
In one of the former papers I mentioned the fact that 
the mixture used for artificial fertilization killed the sperma- 
tozoa in a comparatively short time and injured many of 
the eggs. Contrary to the common prejudice, it is a fact 
that spermatozoa are much more sensitive and are killed 
much sooner than the egg. 
My experiments at Pacific Grove were carried on with 
Strongylocentrotus franciscanus and S. purpuratus. In both 
animals artificial parthenogenesis can easily be accomplished. 
In the experiments at Pacific Grove I enjoyed the valu- 
able assistance of Mr. W. E. Garrey. 
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