592 STUDIES IN GENERAL PHYSIOLOGY 



cells. Some had even gone a little farther. 1 But then the 

 segmentation stopped. No egg had a membrane. 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. y n MgCl 2 + 2 c.c. ^ n CaCl 2 + 

 2 c.c. -|n KC1. 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 no farther. 

 In a mixture of 75 c.c. l -J> n MgCL with 25 c.c. distilled 



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water a small number of unfertilized eggs segmented. In 

 equal parts of *- n MgCl 2 and -|w NaCl no eggs segmented. 

 In Mead's experiments it was KC1 that caused the eggs 

 of Chsetopterus 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. -|w KC1. 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 j l ^n NaHO caused an increase 

 in the rate of development and growth of the unfertilized 

 Arbacia egg, while the equally small addition of an acid 

 (HC1) produced the opposite effect. This summer I tried the 

 effect of HO and H ions upon the unfertilized egg. The 

 following solutions were prepared: 



1 1 am now inclined to believe that the normal concentration of the sea- water 

 was slightly less than that of a g n NaCl solution, and that this beginning of a 

 I arthenogenetic development was due to the fact that the solution used was slightly 

 hypertonic. [1903J 



