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.! 
It is very important that the eggs should not remain too 
jong 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,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,OH are much more effective 
than strong bases like NaOH, KOH, or tetraethylammonium- 
hydroxide. To three solutions of 50 ¢e.c. m/2 Ringer were 
added 0.3 c.c. N/10 NH,OH, 0.3 c.c. N/10 NaOH, and 0.3 c.e. 
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. 23 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. 
