ORIGINAL METHOD OF ARTIFICIAL PARTHENOGENESIS 103 



generally, though possibly not always, unable to cause the 

 unfertilized eggs of S. purpuratus to develop into larvae, no 

 matter how long the egg is exposed to such a solution. For such 

 experiments the alkaline sea-water cannot be used; hence the 

 writer chose as a neutral solution a neutral mixture of 100 

 c.c. NaCl, 2.2c.c. KC1, 1.5c.c. CaCl 2 , and 11. 6 c.c. MgCl 2 , 

 all the solutions being half grammolecular. 



We call such a van't Hoff solution neutral when it 

 is colored red by neutral red, but turns to orange for a few 

 minutes on the addition of only 0.1 c.c. of N/100 NaOH, 

 afterward becoming red again. The concentration of the 

 hydroxy lions in such a solution lies below 10 ~ 6 normal, but so 

 close to this value that the slightest addition of alkali brings 

 up the concentration of the HO ions to this amount; however, 

 owing to the diffusion of the C0 2 of the air into the solution, 

 the concentration of the HO ions soon sinks again below the 

 limit of 10~ 6 n. 



We shall now illustrate by a few examples the fact that 

 even the greatest increase in osmotic pressure will as a rule not 

 effect the transformation of eggs of S. purpuratus into larvae in 

 neutral solution. To 50 c.c. of a neutral van't Hoff solution, 

 8, 12, 16, 24, and 32 c.c. of 2 m KC1 solution were added 

 respectively. The eggs of one female were divided among these 

 solutions after being washed twice in the van't Hoff solution 

 to free them from any trace of sea-water. This precaution 

 is essential in such investigations, and has been employed in all 

 our experiments. The temperature of the hypertonic solution 

 was 13 C. A portion of the eggs was transferred from each 

 solution to normal sea-water after 25, 45, 75, 105, 145, 185, and 

 220 minutes. Not a single egg developed into a larva. With 

 the addition of 32 c.c. of 2J m KC1 to 50 c.c. of the van't Hoff 

 solution the limit of the permissible osmotic pressure is reached, 

 since at higher osmotic pressures the eggs are at once cytolyzed. 1 



iLoeb, Pfliiger's Archiv, CIII, 257, 1904; Untersuchungen ueber Hie kiinst- 

 liche Parthenogenese, pp. 288 ft. 



