150 PROBLEMS OF FERTILIZATION 



the cell is finally the same in both fertilized and unfer- 

 tilized eggs, thus again demonstrating a membrane 

 effect. Eggs which have been treated with partheno- 

 genetic agents show an increase of permeability compa- 

 rable to that of f ertilized eggs, but of a more fluctuating 

 character. 



14 



FIG. 18. Imbibition of water by Arbacia eggs in diluted sea- water 

 (60 volumes tap water plus 40 volumes sea- water). The curves are 

 measurements of diameters at different intervals after placing in diluted 

 sea-water. Ordinates are diameters in micra, abscissae minutes after 

 placing in the hypotonic medium. A, fertilized eggs; B, eggs with 

 artificial membranes; C, unfertilized eggs (after R. S. Lillie). 



In the reverse experiment, of subjecting fertilized 

 and unfertilized eggs to the action of hypertonic sea- 

 water, R. S. Lillie (1918) has shown that fertilized 

 eggs lose water much more rapidly, as is to be expected ; 

 and the two kinds of eggs can thus be separated by 

 gravity in tall tubes of hypertonic sea- water. 



