ACTIVATION OF EGGS OF SEA URCHIN. 1 05 



of purpuratus by a treatment with a hypertonic solution (without 

 artificial membrane formation) it is found that this is possible 

 only with the eggs of certain females. Such eggs develop into 

 plutei. In the eggs of other females a small percentage of eggs 

 will begin to segment and they may go to the 2, 4, 8, or 

 i6-cell stage or still a little further but then stop developing. 

 Such eggs will go into the resting stage again and are normal to 

 all external appearances. If fertilized with sperm a number of 

 hours or a day later the individual blastomeres will each form a 

 special fertilization membrane and develop into small but appa- 

 rently, perfect larvae. 1 This experiment shows that the activating 

 effect which the hypertonic solution had was reversed, since 

 all these eggs were at first in the state of active development. 2 



3. The writer wishes to report in this paper the fact that in 

 the egg of purpuratus under definite conditions a membrane 

 formation can be produced by butyric acid which leads neither 

 to any development if followed by the usual treatment with a 

 hypertonic solution nor to a rapid disintegration when not fol- 

 lowed by any "corrective" treatment. Since in all previous 

 observations on the effects of membrane formation by butyric 

 acid the reverse was found it seemed of theoretical importance 

 to study this exception. 



The main condition for the experiment is that the eggs are 

 put after the treatment with butyric acid into a w/2 solution of 

 NaCl + KC1 + CaCl 2 instead of into sea- water; the various salts 

 are always used in the proportion in which they are contained 

 in sea-water. The eggs were first washed three times in a mix- 

 ture of m/2 NaCl + KC1 + CaCl 2 and were then put for from 

 one and a half to two and a half minutes into a mixture of 50 c.c. 

 m/2 NaCl + KC1 + CaCl 2 + I c.c. Nfio butyric acid; from 

 here they were transferred into a neutral or a slightly alkaline 

 solution of m/2 NaCl + KC1 + CaCl 2 . In this solution all 



1 Loeb, Arch. f. Entwcklngsmech., XXIII., 479, 1907; "Artificial Partheno- 

 genesis and Fertilization," Chicago, 1913, p. 237. 



2 Only the activating effect of the hypertonic solution is reversible, the second, 

 corrective effect, which the hypertonic solution imparts to the egg was not reversed 

 since these blastomeres develop also if only the artificial membrane formation is 

 induced in them by butyric acid, while without the previous treatment with a 

 hypertonic solution such eggs would soon perish. Loeb, Jour. Exper. Zoo/., XV., 

 201, 1913; "Artificial Parthenogenesis and Fertilization," p. 238. 



