24 E. E. JUST. 



dently, Lillie's assumption "that all free fertilizin is fixed at the 

 moment of fertilization or membrane formation" is correct. 



(6) Eggs with Butyric Acid Membranes. If eggs be success- 

 fully treated with butyric acid (optimum exposure to optimum 

 concentration of butyric acid in sea-water) they form membranes. 

 In highly successful cases one may obtain one hundred per cent, 

 membranes. These eggs behave as do eggs with fertilization 

 membranes. If washed by repeated removal of the supernatant 

 sea-water they cease producing fertilizin within two hours after 

 five or six washings. If eggs be washed by removal directly to a 

 large quantity of sea-water the residual fertilizin (in the jelly 

 which may not be removed by butyric acid) is washed away so 

 that when tested these eggs are negative; while an equal bulk of 

 unfertilized eggs without jelly suspended in a like amount of 

 sea- water will still give the reaction. 



We may conclude that after membrane formation induced by 

 sperm or by butyric acid eggs no longer secrete fertilizin. 



According to Lillie's studies, and likewise Moore's account 

 ('16), fertilization capacity and fertilizin production in Arbacia 

 run parallel. I have found the same to be true in Platynereis 

 and Nereis. Farther, Nereis exhibits a very striking phenomenon 

 for even slight washing renders impossible initiation of develop- 

 ment by warming. In the eggs of Echinarachnius the measure 

 of fertilizability is agglutinin production. 



C. Summary of Part II. 



We have shown (i) that Echinarachnius eggs in sea-water 

 liberate a substance that agglutinates Echinarachnius sperm. 

 This substance, fertilizin, which can be quantitatively studied is 

 formed most abundantly in fully ripened (shed) eggs. The 

 substance is lost by eggs repeatedly washed. It is formed by 

 ripe eggs with or without jelly but is not formed by immature 

 eggs nor is it found in perivisceral fluid. (2) . Fertilizin production 

 is an index of fertilization capacity. Eggs highest in fertilizin 

 content, shed eggs, fertilize in largest numbers. Washing the 

 eggs decreases both the fertilizin secretion and the percentage 

 of fertilization. Eggs normally resistant to fertilization yield 

 little fertilizin. After membrane formation fertilizin production 

 ceases. 



