388 



RALPH S. LILLIE 



TABLE 6 



sile strength undergo change during the first few minutes after 

 separation from the egg-surface. This suggests properties 

 hke those of a secretion which hardens on contact with sea-water, 

 such as the secretion forming the resistant chorion of Fundulus 

 eggs. Most observations indicate, however, that the fertihza- 

 tion-membrane is really the separated surface-lamella of the 

 unfertilized egg.^' Previously to fertilization this apparently 

 forms an intimate part of the outer protoplasmic layer or cortical 

 zone; probably it then partakes in the metabolism of the latter 

 and its semi-permeability is thus preserved.^- When the egg 

 responds to the membrane-forming agent, the surface lamella 

 is separated from the cell-surface, possibly forced outward by 

 the osmotic pressure or secretion-pressure of the surface-proto- 

 plasm; its properties then change, perhaps because of the cessa- 

 tion of metabolism. Heilbrunn also describes observations 

 indicating physical changes in the membrane after separation; 

 these changes are in the direction of an increase of permeability 

 to salts; according to the above observations this change runs 

 parallel wdth a loss of extensibility. ^^ 



'1 Cf. my paper in Amer. Journ. Physiol., 1911, vol. 27, p. 300; L. Heilbrunn, 

 Biol. Bull., 1915, vol. 29, p. 158. 



^^ The preservation of semi-permeability is a function of cell-metabolism ; 

 cf. my recent paper, loc. cit, 1916, p. 265. 



^' Compare Heilbrunn, loc. cit., p. 160. Heilbrunn infers an increased rigidity 

 in the membrane, due to a coagulative and dehj^drative change in its substance 

 (p. 167). 



