XI 



FURTHER EXPERIMENTS ON THE ACTION OF THE 



HYPERTONIC SOLUTION AFTER MEMBRANE 



FORMATION 



1. The most convenient and reliable method of saving the 

 eggs of the sea-urchin from disintegrating after artificial mem- 

 brane formation consists in subjecting them to a short exposure 

 to hypertonic sea-water. If they are then transferred at the 

 right time from this hypertonic solution to normal Sea-water, 

 they all segment and develop into larvae; and in a certain per- 

 centage of these larvae the development is perfectly normal. 



Why do not all the eggs so treated produce normal larvae ? 

 In order to understand this we must consider two facts. If the 

 eggs are left too short a time in the hypertonic solution, the 

 threatening disintegration is not prevented and the eggs go to 

 pieces precisely as though no hypertonic solution had been 

 used. If the eggs are left too long in the solutioii they do 

 indeed all develop into larvae, but the larvae are abnormal; 

 the farther the proper moment for transference of the eggs to 

 normal sea-water has been overshot, the more abnormal the 

 larvae are and the earlier they die. 



Now the proper length of exposure to the hypertonic solu- 

 tion is not the same for all eggs. Even if the eggs of the same 

 female are used, exposed for the same length of time to the 

 fatty acid and placed for the same time in the same hypertonic 

 solution, it will be found that the correct time of exposure varies 

 within fairly wide limits for different eggs. This can easily be 

 seen if the eggs are brought back from the hypertonic solution 

 into normal sea-water at intervals of five minutes. Perhaps 

 none of the eggs first returned to normal sea-water develop, 

 until one reaches a portion in which all grow into larvae; but 



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