148 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



the membrane. This membrane does not usually form while 

 the eggs are in the alkaline solution but afterward either in the 

 hypertonic solution or sometimes even later. 1 



'It is very important that the eggs should not remain too 

 long in the hypertonic solution. The time they must remain in 

 the hypertonic solution varies according to the length of time 

 the eggs remained in the NH 4 OH solution. Eggs that were 

 kept in the above-mentioned alkaline solution for ten minutes 

 developed best when they were exposed to the hypertonic 

 solution for twenty-four minutes; while eggs that were in the 

 alkaline solution for thirty minutes developed best when put 

 for fifteen minutes into the hypertonic solution. This observa- 

 tion finds its possible explanation in the fact that the hyper- 

 tonic solution also causes an increase in the rate of oxidation 

 of the unfertilized egg, and in this respect resembles the action 

 of the alkaline solution. It is therefore not surprising that the 

 two solutions can act as a partial substitute for each other. If 

 the eggs remain only a few minutes too long in the hypertonic 

 solution, they suffer considerably ; if they are taken out of the 

 hypertonic solution too soon, they will not develop. 



2. A comparison of the relative efficiency of various alkalies 

 for the causation of artificial parthenogenesis furnished the 

 result that weak bases like NH 4 OH are much more effective 

 than strong bases like NaOH, KOH, or tetraethylammonium- 

 hydroxide. To three solutions of 50 c.c. m/2 Ringer were 

 added 0.3 c.c. N/10 NH 4 OH, 0.3 c.c. N/lONaOH, and 0.3 c.c. 

 N/10 tetraethylammoniumhydroxide respectively. Unferti- 

 lized eggs of Arbacia were put into these solutions for twenty- 

 six minutes and were then transferred to the hypertonic Ringer 

 solution (50 c.c. m/2 Ringer +8 c.c. 2f m Ringer). They 

 remained here for fifteen minutes and were then transferred 

 to normal sea-water. Practically all the eggs that had been 



1 Loeb, "The Comparative Efficiency of Weak and Strong Bases in Artificial 

 Parthenogenesis," Jour. Exper. ZooL, XIII, 577, 1912. 



