FERTILIZATION MEMBRANE OF ASTERIAS AND ARBACIA EGGS. 293 



Again, in the formation of the blastula the cells range up close 

 to the inner surface of the fertilization membrane and completely 

 obliterate the interior space giving a further indication that 

 neither a thickened vitelline membrane nor any "gel" is there. 



These demonstrations may be made immediately after fertiliza- 

 tion so that there is no necessity to assume that the vitelline 

 membrane or a gel in -the perivitelline space has had time to 

 undergo liquefaction. 



The above facts and others which might be referred to all 

 indicate the fluid character of the contents of the space between 

 the fertilization membrane and the egg surface and serve to 

 substantiate the conception of the fertilization membrane stated 

 in the opening paragraph of this communication. In the case of 

 both Arbacia and Asterias the fertilization membrane is a struc- 

 ture which arises at the surface of the egg and is subsequently 

 lifted from it and distended by fluid. Depending upon the 

 time of fertilization of Asterias eggs relative to the formation of 

 the polar bodies these structures may be outside the fertilization 

 membrane, inside the perivitelline space or the first outside 

 and the second within the fertilization membrane. 



Heilbrunn 1 has reviewed the subject of membrane production 

 by Arbacia eggs under the influence of various chemicals. He 

 concludes with Herbst and others that in this form the membrane 

 exists preformed on the surface of the unfertilized egg and that 

 fertilizing agents merely cause its elevation. He gives evidence 

 in support of the view that this elevation is the result of lowering 

 of surface tension and swelling of proteins beneath the membrane. 

 In the light of our findings it is clear that the fluid character of 

 the contents of the intra-membranal space and the progressive 

 increase in its bulk as the membrane is lifted away from the egg 

 indicate that the colloids are in solution and that the process 

 involves the osmotic attraction of water. 



It is not yet demonstrated that a membrane exists preformed 

 on the surface of unfertilized Asterias egg and the formation of a 

 membrane on a fragment of Arbacia egg as described by Moore 

 (loc. cit.) are facts which speak, in these instances, for the forma- 

 tion of the fertilization membrane de novo. 



1 Heilbrunn, Lewis V., BIOL. BULL., 1913, XXIV, p. 343. 



