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 Arbada also Mg ions 

 play no specific r61e, 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 MgCl2, NaCl, 

 KCl, or CaCl2, or by the addition' of non-electrolytes such as 

 cane sugar and urea. The experiments upon the eggs of Arbada 

 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 MgCl2 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°.^ 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.c. m/2 CaCl2:12c.c. m/2 MgCla) the lowering 

 of the freezing-point is somewhat greater, viz., about 1.84°. 



>Loeb, "Further Experiments on Artificial Parthenogenesis and the Nature 

 of the Process of Fertilization," Am. Jour. Physiol., IV, 178, 1900; Untersuchungen 

 ueher kUnsiliche Parthenogeneae, p. 154. 



'W. E. Garrey, "The Osmotic Pressure of Sea- Water and of the Blood of 

 Marine Animals," Biol. Bull, VIII, 257, 1905. 



