LARVAE OF ARBACIA PUNCTULATA 



391 



Fischel ('09) used solutions of N/2 NaCl with sea-water in 

 various proportions in his experiments with Echinus* micro- 

 tuberculatus, Strongylocentrotus Hvidus and Arbacia pustu- 

 losa. Only in the case of the first named did he obtain an 

 acceleration in the rate of development; in the other two the 

 opposite effect was produced. When he subjected the eggs of 

 Arbacia, one half hour after fertilization, for the brief period 

 of 30 minutes to a mixture of 87.5 parts sea-water to 12.25 

 parts 0.50M NaCl, they developed much more slowly than did 

 the control. The inhibition was not especially apparent during 

 cleavage, but appeared after blastula formation. He figures 

 two which had been treated in this manner and at 3 days 20 

 hours and 4 days 18 hours respectively, they had not passed 

 beyond a late gastrula stage. If this reaction of Arbacia pustu- 

 losa is typical, either some fundamental difference must exist 

 between punctulata and the species employed by Fischel, or 

 profound disturbances were set up when the embryos w^ere 

 transferred from the experimental solution back to sea- water. 

 The slight change of osmotic pressure involved seems hardly 

 adequate to account for the extensive injury incurred. Rather 

 it seems necessary to conclude that the two species respond in a 

 fundamentally different way to similar experimental conditions. 



In order to ascertain the effects of NaCl in hypertonic solu- 

 tion without dilution of the other constituents of sea-water, 

 the salt was added directly to the sea-water in the following 

 amounts : — 



Experiments 18 and 19 



a Sea-water 



b lOOcc. S. W. + 0.255g. NaCl 



c 100 cc. S. W. + 0.375g. NaCl 



d 100 cc. S. W; + 0.50 g. NaCl 



From these two experiments with similar solutions, the follow- 

 ing results were obtained: 



Experiment 18. Plot 17. September 9, 1914.. Tables 11 to U 



