Vol. XXVII. Xm'cmber, 1914. No. 5 



BIOLOGICAL BULLETIN 



IS THE FERTILIZATION MEMBRANE OF ARBACIA 

 EGGS A PRECIPITATION MEMBRANE? 



E. NEWTON HARVEY, 

 PRINCETON UNIVERSITY. 



In 1912 McClendon ('12) suggested that the fertilization 

 membrane of sea urchin eggs is a precipitation membrane formed 

 when t\vo colloids of opposite electrical charge meet, namely the 

 negative egg jelly (mucous, zona pellucida) and a positive 

 substance secreted by the egg. Elder ('13) has advanced a 

 similar view and recently McClendon ('14) has restated his 

 former opinion. Of course the test of the theory is perfectly 

 simple. An unfertilized egg from which the jelly has been 

 removed should form no membrane when fertilized, and both 

 McClendon and Elder state that this is the case. 



I have utterly failed to confirm these statements and find 

 that whether an egg forms a normal membrane or not is abso- 

 lutely independent of the jelly which surrounds it. My method 

 of determining this is as follows: Eggs from one female are 

 divided into two parts and the jelly removed from the eggs of 

 one part by shaking two or three times in a test-tube and wash- 

 ing with sea water. Eggs of both lots are placed together upon 

 a slide and india ink suspension, sperm, and, after mixing, a cover 

 glass is added. It is perfectly easy to see which eggs are sur- 

 rounded by jelly and which are not. All of them, whether with 

 or without jelly, form fertilization membranes which in the two- 

 cell stage surround the whole egg and are quite distinct from the 

 hyaline plasma layer which is close to each blastomere. An egg 

 without jelly touching the jelly of another egg should form a 

 membrane, according to McClendon's idea, only on the side 

 toward the jelly. Yet such a condition is never observed, but 

 instead a membrane forms about the whole egg. Thus eggs 

 without jelly will form fertilization membranes. 



237 



