128 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



If we compare these results with those obtained in chapter 

 xi, we find that 50 c.c. of m/2 NaCl+5 c.c. of 2J m NaCl 

 produce the same effect as 50 c.c. of sea-water +4 c.c. of 

 2J m NaCl; in other words, that a mixture of 50 c.c. of J m 

 NaCl+1 c.c. of 2| m NaCl is about isotonic with sea-water. 



TABLE XIV 



COMPOSITION OF THE SOLUTION 



PERCENTAGE OF EGGS THAT 



DEVELOPED INTO LARVAE 



AFTER AN EXPOSURE OF 



Now whereas a mixture of 50 c.c. of sea-water +10 c.c. of 

 2J m NaCl injures the eggs so badly in 60 minutes that only a 

 small number develop, and a mixture of 50 c.c. of sea-water + 

 12 c.c. of 2| m NaCl kills practically all eggs with artificial mem- 

 branes in 60 minutes, in a mixture of 50 c.c. of \ m NaCI+16 c.c. 

 of 2J m NaCl 80 per cent of the eggs develop after an exposure 

 of 55 minutes. The explanation of this paradox lies in the fact 

 that the NaCl solution was practically neutral, while the sea- 

 water is slightly alkaline. We shall see in a later chapter that 

 the harmful effect of hypertonic solutions upon the egg is much 

 greater if they are slightly alkaline than when they are neutral ; 

 slightly acid hypertonic solutions are still less injurious than 

 neutral ones, or, in other words, the harmful effect of hypertonic 

 solutions increases, within the limits considered, with the con- 

 centration of the hydroxylions. The injurious effect of these 

 hypertonic solutions is diminished, if not absent, in a solution 



