242 L. V. HEILBRUNN. 



gate the action of the mercuric chloride, with a view to the 

 possible abandonment of the surface tension theory. Although 

 many experiments were performed, only a few of them will be 

 considered and these rather hastily. They suffice to show that 

 the action of mercuric chloride is not a simple one. 



If an m/io solution of mercuric chloride is diluted a thousand 

 times with sea-water, then an " w/io,ooo solution of mercuric 

 chloride in sea-water " is obtained. A solution of this sort is very 

 favorable to membrane elevation. Solutions decidedly more 

 concentrated than m/io,ooo do not act as well. In an ra/iooo 

 solution, the membranes, if they lift off at all, become only 

 partially elevated, apparently they stick to several points of the 

 egg surface as they attempt to lift away from it. On the other 

 hand extreme dilutions are also ineffective, although it is possible 

 to obtain good membrane elevation in solutions as weak as 

 w/ioo,ooo. Thus there is a wide range of concentration in 

 which the mercuric chloride is effective. Most of the experi- 

 ments were made with an w/io,ooo solution (in sea-water). 



On exposure to the mercuric chloride, membrane elevation 

 does not occur immediately. After 3 or 4 or 5 minutes, the 

 membranes can be seen rising from the surface of the eggs. 

 The effect of the sublimate is not solely a cortical effect. After 

 eggs have been exposed for about 12 minutes other changes 

 may begin to appear. In many cases the cell undergoes what is 

 apparently a cell division. At any rate it becomes constricted. 

 Usually this constriction divides the egg unequally, a large cell 

 and a small cell are formed. In such cases of unequal division 

 the smaller cell usually contains a mass of pigment and the 

 larger cell is comparatively colorless. Now and then instead of 

 an unequal division there is a furrow around the very center of 

 the egg with an accumulation of pigment granules underneath 

 the furrow. No attempt was made to discover whether nuclear 

 changes accompanied the changes in the cytoplasm. If the 

 constrictions of the cytoplasm do represent anything at all 

 comparable to a normal cell division, it is surprising that they 

 occur so soon after the eggs are exposed to the mercuric chloride. 

 Typically the Arbacia egg does not divide until 50 or 60 minutes 

 have elapsed after fertilization. The cytoplasmic constrictions 



