Artificial Parthenogenesis 99 



ment with hypertonic sea water or with lack of oxygen 

 or with KCN they developed into normal larvae. 

 This new or improved method of artificial partheno- 

 genesis is as follows: The eggs are put for from two to 

 four minutes into 50 c.c. sea water containing a certain 

 amount of N/io butyric acid (2.6 c.c. in the case of S. 

 purpuratus in California and 2.0 c.c. in the case of 

 Arbacia in Woods Hole). Ten or fifteen minutes later 

 the eggs are put into hypertonic sea water (50 c.c. sea 

 water +8 c.c. 2j^ m NaCl or Ringer solution or cane 

 sugar) in which they remain, at 15 C. from thirty-five 

 to sixty minutes in the case of purpuratus, and from 

 17^ minutes to 22^ minutes at 23 in the case of 

 Arbacia at Woods Hole. If the eggs are then trans- 

 ferred to normal sea water they will develop. In 

 making these experiments, which have been repeated 

 and confirmed by numerous investigators, it should be 

 remembered that this effect of the hypertonic solution 

 has a high temperature coefficient (about two for 

 10 C.) and that a slight overexposure to the hyper- 

 tonic sea water injures the eggs so that development is 

 abnormal. By this method it is possible to imitate the 

 activating effect of the living spermatozoon upon the 

 egg in every detail and eggs treated in this way will 

 develop in large numbers into perfectly normal larvae. 

 We shall see later that they can also be raised to the 

 adult state. 



2. The next task was to find out the nature of the 



