IMPROVED METHOD OF ARTIFICIAL PARTHENOGENESIS 71 



It is, moreover, necessary that not too many eggs be put 

 into one bowl of hypertonic sea-water, since otherwise a mutual 

 struggle for oxygen takes place. The eggs should also be kept 

 in shallow dishes so that the layer of water which covers them 

 may not be too deep and the diffusion of oxygen from the air to 

 the eggs not too greatly hindered. I usually cover the bowls 

 loosely with a glass plate. 1 



I have since tried the same method with success on the eggs 

 of Arbacia at Woods Hole. As was to be expected, the quanti- 

 tative data of the method are a little different in this case from 

 those found in S. purpuratus. The eggs were put into a mix- 

 ture of 50 c.c. sea-water +2 c.c. N/10 butyric acid for from one 

 and one-half to three minutes. When transferred to sea-water 

 they did not form a conspicuous fertilization membrane, as did 

 the eggs of S. purpuratus under the same circumstances, but 

 only a fine gelatinous layer which was not easily visible. Ten 

 or fifteen minutes later the eggs were transferred to hypertonic 

 sea-water (50 c.c. sea- water +8 c.c. 2J m NaCl). In this solu- 

 tion the eggs remained at a temperature of about 23 only from 

 seventeen and one-half to twenty-five minutes, after which 

 they were transferred to normal sea-water. Since the time 

 during which the eggs must remain in the hypertonic solution 

 varies for the individual eggs and since a slight over-exposure 

 in the hypertonic solution seriously injures the eggs, it is advis- 

 able to transfer the eggs not all at the same time but at intervals, 

 e.g., after seventeen and one-half, twenty, twenty-two and 

 one-half, and twenty-five minutes. Eggs which were exposed 

 longer than twenty-five minutes to the hypertonic solution did 

 not develop. 



The same method has been applied successfully, among 

 others at Naples by Herbst, Warburg, and by Meyerhof, and 

 at Plymouth by Shearer and his pupils. 



1 Other factors which have to be considered in this method will be mentioned 

 in the next chapter. 



