FERTILIZATION MEMBRANE OF ASTERIAS AND ARBACIA EGGS. 2QI 



by the egg and separated from its surface by a liquid filled space 

 as is indicated by the following considerations: 



1. This new structure has entirely different permeability from 

 that of the surfaces of either the fertilized or unfertilized eggs 

 which are very slightly permeable to neutral salts, so that the 

 eggs are plasmolyzed and crenated by hypertonic saline solutions. 

 Salts however must penetrate the fertilization membrane freely 

 to effect this change in the egg and that they do so is further 

 shown by the fact that the fertilization membrane retains its 

 round contour and distended condition when placed in the hyper- 

 tonic or hypo-tonic salt solutions. The differences in permea- 

 bility thus far demonstrated speak against the origin of the 

 membrane from a pre-existing structure on the surface of the egg. 



2. Kite's description is proven incorrect by the demonstration 

 of the fact that the fertilization membrane is separated from the 

 surface of the egg by a space filled with liquid and not occupied 

 by a swollen gelatinous vitelline membrane continuous with the 

 surface of the egg on the inside and with the egg jelly on the 

 outside. Dr. Robt. Chambers by removing this liquid from this 

 space for me by the use of his micro-pipette has produced a 

 collapse of the membrane. Allusion has already been made to 

 the fact that polar bodies extruded after the formation of the 

 fertilization membrane may be separated from the egg surface 

 by manipulation and are then free to assume various positions 

 in the space; this could be possible only in liquid but certainly 

 not if the space was occupied by any sort of a "gel." 



Professor J. Loeb has shown that the fertilization membrane 

 of echinoderms is impermeable to such colloids as egg white, 

 shark's serum, and even tannic acid. These materials, if added 

 to sea water, cause the thin membrane to crumple onto the 

 surface of the enclosed egg by the osmotic extraction of water 

 from the intervening space; but the membrane regains its original 

 contour when replaced in sea water. This latter fact suggested 

 to Loeb the probability that the space contains some colloid in 

 solution secreted by the egg at the time the fertilization mem- 

 brane is formed. To this colloid the membrane is impermeable; 

 it therefore exerts its osmotic pressure in excess of that due to 

 the salts of the sea water, serves to raise the membrane from the 

 surface of the egg and to keep it distended. 



