ORIGINAL METHOD OF ARTIFICIAL PARTHENOGENESIS 107 



In this case the NaOH had little effect and hence the 

 hypertonicity caused a noticeable increase in the rate since it 

 probably increased the number of eggs in which the process of 

 membrane formation was started. 



TABLE XXXV 



4. It is necessary for the developmental effect that the 

 hypertonic solution contain free oxygen. If the oxygen is 

 driven out of a hypertonic solution sufficiently thoroughly, 

 this solution can no longer cause the unfertilized eggs of the 

 sea-urchin to develop. The following experiment on the eggs 

 of S. purpuratus will serve as an example. The air was driven 

 out of a series of flasks each of which contained 50 c.c. 

 of sea-water +8 c.c. 2J m NaCl, 1 by passing chemically 

 pure hydrogen through them for several hours, and then 

 a pipette full of sea-urchin eggs was introduced into each 

 of them. This was effected with the aid of an assistant and in 

 such a way that the stopper of the flask was lifted to one side 

 over the rim for only one or two seconds and during this time 

 the pipette that had been held in readiness was emptied into 

 the flask. The current of hydrogen was not interrupted and 

 proceeded throughout the whole experiment. Some of the eggs 

 were placed as a control in 50 c.c. of sea-water-f 8 c.c. of 2J m 

 NaCl which remained in contact with air. After 128 and 180 

 minutes samples of the eggs were replaced in normal sea-water. 

 The control eggs which had been in the oxygenated sea-water 

 and were transferred to normal sea-water after 128 minutes 

 developed practically all into larvae; of the eggs transferred to 



1 This hypertonic solution was slightly alkaline. 



