238 E. NEWTON HARVEY. 



If Arbacia eggs are allowed to stand for about 52 hours at a 

 temperature of 22 C. or for 3 to 4 days at a temperature of 

 12 C. no membranes form despite the fact that they may still 

 be surrounded by a copious amount of jelly. This observation 

 so far as I am aware was first made by Loeb ('03) and confirmed 

 by myself ('10) and F. R. Lillie ('14). In the two-cell stage the 

 blastomeres are widely separated because not surrounded by a 

 fertilization membrane although the hyaline plasma layer is 

 clearly visible. 1 Thus even an egg surrounded by jelly may fail 

 to form a fertilization membrane. 



I at first thought that McClendon's observations were due 

 to the fact that he took so long a time in removing the jelly, 

 (agitation and washing for "not more than 24 hrs.") that the 

 mere age of the eggs would account for their inability to form 

 membranes. I find, however, that the eggs with jelly must stand 

 for over 52 hrs. at 22 C. before they are unable to form a ferti- 

 lization membrane. 



This fact suggests that the membrane-forming substance 

 (membranogen) which passes out of the egg to form the mem- 

 brane gradually diffuses away or is used up when the egg is 

 allowed to stand. Since the membranogen is probably a protein 

 we should expect it to diffuse away from the eggs without jelly 

 much more readily than from those eggs with jelly. It is well 

 known that colloids do not readily diffuse through each other. 

 Such is actually the case and in this point lies, I believe, the 

 explanation of McClendon's results. If we take the eggs from 

 one female, remove the jelly from one lot by shaking, but allow 

 it to remain on the other lot, both lots will form perfectly normal 

 membranes if fertilized immediately. If both lots are allowed 

 to stand for 24 hrs. and are then fertilized the eggs which have 

 stood without jelly form no membranes while those with jelly 

 form membranes only slightly thinner than normal. Membrane 



1 The hyaline plasma layer appears much thicker than in freshly fertilized eggs 

 and in my previous paper ('10) I described this as a special type of membrane. 

 However there is nothing present at all comparable to the normal fertilization 

 membrane and without quibbling over minute distinctions we may safely class 

 these eggs as "without membranes." McClendon ('14) misquotes me instating 

 that I believe the fertilization membranes to be present on unfertilized eggs and to 

 be simply lifted off after fertilization. I have held exactly the opposite view 

 (Harvey, '10). 



