98 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



2. We will now inquire how the time which the eggs must 

 remain in the hypertonic solution varies with the osmotic pres- 

 sure of the latter. 1 



The eggs of a sea-urchin were treated with sea-water con- 

 taining butyric acid, and all formed membranes. The eggs 

 were then distributed among solutions consisting of 50 c.c. of 

 sea-water +respectively, 0, 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, and 

 14 c.c. of 2J m (grammolecular) NaCl solution. A portion of 

 the eggs was transferred from each of these solutions to normal 

 sea-water after 33, 45, 57, 68, 98, and 128 minutes, and the 

 percentage that developed into larvae determined for each 

 portion. Table VII gives the result. The temperature of the 

 hypertonic solution was 16 C. 



TABLE VII 



NATURE OF THE SOLUTION 



PERCENTAGE OF THE EGGS OF 



S. purpuratus WHICH DEVELOPED 



INTO LARVAE AFTER REMAINING IN 



THE SOLUTION 



This brings out two facts. In the first place the effective- 

 ness of the hypertonic solution has definite limits. The addi- 

 tion of 4 c.c. of 2J m NaCl is too small, the addition of 12 c.c. too 

 much, and in the latter case the eggs go to pieces by disinte- 

 grating into drops. Secondly, we see that when once the opti- 

 mum concentration is reached, i.e., that which produces the 



1 Loeb, "Ueber den Unterschied zwischen isosmotischen und isotonischen 

 Losungen bei der kunstlichen Parthenogenese," Biochem. Zeitschr., XI, 144, 1908. 



