THE BIOLOGY OF THE CELL SURFACE 



the egg decreases because "the former is freely permeable 

 to electrolytes whereas the latter is not"?^ The answer is 

 simple: the existence of such a difference has actually not 

 been proved. 



The correct interpretation of the changes in sea-urchins' 

 eggs induced by means of sea-water made hypertonic by the 

 addition of either electrolytes or non-electrolytes is as fol- 

 lows: placed in hypertonic sea-water, the whole egg, includ- 

 ing its ectoplasmic filaments, loses water and shrinks. The 



Fig. 36. — Cleavage of an egg of Echinus microtuherculatus in calcium-free 

 sea-water (after Herbst). The covering membrane of the ectoplasm is destroyed, 

 leaving the filaments free. 



filaments decrease in diameter and appear as lines thereby 

 becoming more easily visible. In every tgg known to me, 

 the ectoplasmic filaments appear in the same way as an 

 effect of hypertonicity.- 



We can not escape these facts: that after fertilization and 

 with membrane separation the surface of the egg is studded 

 with filaments; and that also unfertilized eggs as they shrink 

 in hypertonic sea-water show these filaments. It is patent, 

 therefore, that the filaments are not new formations called 

 forth by the action of electrolytes. The action of electro- 

 lytes does not demonstrate a difference in permeability 

 between endoplasm and ectoplasm. 



Gray also errs when he says that the hyaline plasma-layer 

 dissolves in calcium-free sea-water. Rather, eggs in this 



^ Gray, I.e. 



- Cj. Faure-FreDiiet. 



280 



