STUDIES IN ARTIFICIAL PARTHENOGENESIS. 325 



membrane elevation, but not polar body formation. Of the 

 eggs exposed \ minute, 72 per cent, had widely elevated mem- 

 branes. These eggs, however, could not produce polar bodies 

 for they were thoroughly coagulated. This was shown by a 

 viscosity test with the centrifuge. 



MEMBRANE SWELLING. 



If instead of being lifted off, the vitelline membrane is made 

 to swell, much the same effect is produced on the egg. The 

 increased fluidity of the vitelline membrane results in a lower 

 surface tension. 1 Consequently it no longer exerts as great a 

 pressure upon the egg contents. Thus maturation follows mem- 

 brane swelling just as it follows membrane elevation. 



In order to produce a swelling of the membrane the same 

 reagents were used that were previously found to have been 

 effective for the sea-urchin egg. Evidently the vitelline mem- 

 branes of both Cumingia and Arbacia are similar, for they swell 

 under the same conditions. 



Sodium Iodide. Eggs were exposed to 0.6 M sodium iodide. 

 After 15 and 22^ minutes they were removed to sea-water in 

 Stender dishes A and B respectively. Of the eggs in A, 14/100 

 showed polar bodies. The eggs in B formed no polar bodies. 

 The sodium iodide solution caused membrane swelling. 



Hydrochloric Acid. Eggs were placed in 25 c.c. of sea-water 

 plus 0.7 c.c. n/io HC1. After exposures of |, i, 2, 3, 4, 5, 7, 10 

 minutes the eggs were removed from the acid solution and placed 

 in ordinary sea-water in Stender dishes A H respectively. In 

 the acidified sea-water the egg membrane swelled and the surface 

 of the egg became sticky. Often the eggs adhered to the bottom 

 of the dish. Counts of eggs with polar bodies gave the following 

 results: 



A }<2 minute exposure 6/50 



B i 5/50 



C i 10/50 



D 3 4/50 (This count was made too early) 



E 4 13/50 



F 5 IS/50 



G 7 10/50 



H 10 8/50 



1 Many biologists apparently do not understand that solids and pseudo-solids 

 (i.e., gels) exhibit surface tension. This tension is greater for a gel than for the 

 corresponding sol. For references to literature on this subject consult Heilbrunn 

 '15, footnote, p. 166. 



