268 ARTIFICIAL PARTHENOGENESIS AND FERTILIZATION 



NaOH. Some of the eggs that had been exposed to solutions 

 containing more NaOH did develop into larvae ; the percentage 

 of larvae varied according to the alkalinity of the solution and 

 the time the egg was exposed to the solution. Many of the 

 eggs that had been 2| hours in the h^pertonic solution con- 

 taining 0.8 c.c. of NaOH, or 2| hours in that containing 0.4 c.c., 

 developed into larvae. 1 



Hence it can be seen that just as in the case of the eggs of 

 purpuratus and of Polynoe, the hypertonic solution as a rule only 

 affects the eggs of Lottia when a certain degree of concentration 

 of hydroxylions (about 10~ 6 N) has been reached. Further, it 

 is also clear that when the concentration of hydroxylions in the 

 hypertonic solution is higher than in sea-water, the number of 

 larvae formed also increases. But in this case also, as in the 

 experiments with the eggs of S. purpuratus, the optimal con- 

 centration of hydroxylions for the production of larvae is sub- 

 ject to large variations with the eggs of different females. 



The second fact brought out by these experiments is the 

 importance of oxygen. In flat dishes (that are covered against 

 evaporation of the sea-water) in which the eggs lie close to the 

 surface of the water, the number of eggs that develop is appreci- 

 ably higher than in dishes in which the eggs are covered with a 

 deep layer of sea-water. 



Finally, it is a point of interest that no visible membrane 

 formation takes place in these forms. In this respect the eggs 

 behave differently from those hitherto discussed. 



Attempts to separate by an interval of time the effect of the 

 alkali and the raising of the osmotic pressure, as can be done 

 with the eggs of the sea-urchin and of Polynoe, have not yet 

 proved successful with Lottia. Moreover, development is not 

 produced by treatment with alkali alone. 



In all these experiments the eggs developed practically 



1 Loeb, "Ueber die allgemeinen Mebhoden der kiinstlichen Parthenogenese," 

 op. cit. 



