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Osmotic PARTHENOGENESIS 59 
remained entirely, or almost entirely, ineffectual. I could at 
that time assign no reason for this, and postponed the publica- 
tion of these results until I had the opportunity of repeating 
them once more in Woods Hole. In the summer of 1900 I 
convinced myself at Woods Hole that for Arbacia also Mg ions 
play no specific réle, but that it is merely a case of appropriate 
increase of osmotic pressure.' As long as the osmotic pressure 
of sea-water is raised about 50 per cent, it is immaterial whether 
the rise of pressure is caused by electrolytes like MgCl, NaCl, 
KCl, or CaCl, or by the addition of non-electrolytes such as 
cane sugar and urea. The experiments upon the eggs of Arbacia 
at Woods Hole gave much more constant results than the 
experiments on Strongylocentrotus in Pacific Grove. ) The 
reason that in the previous year artificial parthenogenesis was 
successful only when the concentration of the sea-water was 
raised by MgCl, was due to the fact that the solutions of 
salts with which I worked were not isosmotic, as I had sup- 
posed. 
Now as in this treatise we are especially interested in the 
quantitative aspect of this experiment, we must discuss some- 
what more thoroughly the amount of increase of osmotic 
pressure that is necessary for development. According to 
W. E. Garrey, in the sea-water at Woods Hole the freezing- 
point is lowered by 1.818°, while the water flowing in the 
laboratory has a somewhat higher concentration, viz., A= 
1.83°.2 Freezing-point determinations on pure NaCl solutions 
gave for a m/2 NaCl solution A=1.75°, and for a m/2 van’t 
Hoff solution (i.e., for a mixture of 100 c.c. m/2 NaCl:2.2 c.c. 
m/2 KCl:2¢.c. m/2 CaCl,:12¢.c. m/2 MgCl.) the lowering 
of the freezing-point is somewhat greater, viz., about 1.84°. 
1 Loeb, ‘‘ Further Experiments on Artificial Parthenogenesis and the Nature 
of the Process of Fertilization,’’ Am. Jour. Physiol., 1V, 178, 1900; Untersuchungen 
ueber kiinstliche Parthenogenese, p. 154. 
2W. E. Garrey, ‘‘The Osmotic Pressure of Sea-Water and of the Blood of 
Marine Animals,’’ Biol. Bull., VIII, 257, 1905. 
