592 STUDIES IN GENERAL PHYSIOLOGY 
cells. Some had even gone a little farther." But then the 
segmentation stopped. No egg hadamembrane. A second 
lot was put into normal sea-water. Eight hours later none 
of these eggs had segmented or had a membrane. This 
indicates that a mere change in the constitution of the sea- 
water without any change in the osmotic pressure may cause 
the beginning of a segmentation of the egg. A third lot was 
put into a solution of 96 c.c. 1,9 n MgCl, + 2 ¢.c. tf n CaCl, + 
2c.c. $n KCl. No egg segmented. One lot of these eggs 
was put back into normal sea-water five hours later. A few 
eggs now went into the two-cell stage, but developed nofarther. 
In a mixture of 75 cc. 49n MgCl, with 25 c.c. distilled 
water a small number of unfertilized eggs segmented. In 
equal parts of 19 MgCl, and $n NaCl no eggs segmented. 
In Mead’s experiments it was KCl that caused the eggs 
of Chetopterus to throw out their polar bodies. I put 
unfertilized eggs of Arbacia first into sea-water for five 
hours. No eggs showed a trace of beginning segmentation. 
After this the eggs were put for two hours into a mixture of 
90 c.c. sea-water and 10 c.c. $2 KCl. When put back into 
normal sea-water, in fifteen minutes almost every other egg 
began to divide, but the segmentation never went beyond the 
sixteen-cell stage at the best. Neither these nor the above- 
mentioned experiments gave constant results. The greatest 
differences existed in the proportion of eggs that showed a 
segmentation. In a former paper I had proved that the 
addition of a small amount of +; NaHO caused an increase 
in the rate of development and growth of the unfertilized 
Arbacia egg, while the equally small addition of an acid 
(HCl) produced the opposite effect. This summer I tried the 
effect of HO and H ions upon the unfertilized egg. The 
following solutions were prepared: 
1T am now inclined, to believe that the normal concentration of the sea-water 
was slightly less than that of a 8” NaCl solution, and that this beginning of a 
| arthenogenetic development was due to the fact that the solution used was slightly 
hypertonic. [1903] 
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