C. B. METZ 41 



reversed after agglutination with normal fertilizin will be awaited 

 with particular interest. 



The source of fertilizin has been examined seriously in only two 

 forms other than the sea urchin, namely the gastropod, Mega- 

 thura, and the annelid, Nereis. Megathum (Tyler, 1940a) is 

 similar to the sea urchin. The unfertilized egg is suiTOunded by a 

 gelatinous coat. When this coat is removed, no further fertilizin 

 can be obtained from the egg. 



Conditions in Nereis are more complex. The unfertilized egg 

 has no substantial gelatinous coat (Lillie, 1911). However, upon 

 activation of the egg a thick jelly is extruded. The mechanism of 

 this release of jelly has been investigated most recently by Cos- 

 tello (1949). He has shown that the jelly arises by a transforma- 

 tion of certain granules released from the egg cortex. The egg 

 water of unfertilized Nereis eggs contains fertilizin (Lillie, 

 1913b). Therefore release of some fertilizin does not depend 

 upon visible extrusion of the jelly. However, solutions of the 

 jelly, obtained by treating eggs with alkaline sea water (method 

 of Novikojff, 1939; Costello, 1945) give higher spemi agglutina- 

 tion titers than normal egg water controls (Tyler, 1948b). This 

 suggests that the jelly material of the Nereis egg may be the 

 fertilizin. To account for the fertilizin in normal egg water Tyler 

 suggests that some of the jelly material may diffuse from the 

 normal, unfertilized egg. In any event these experiments are 

 evidence that the fertilizin of Nereis is produced by the egg itself, 

 not by follicle cells of the ovary. 



Effect of Removal and Addition of Fertilizin on Fertilizability 

 of the Egg. If fertilizin is essential for fertilization, fertilizin-free 

 eggs should fail to fertilize and fertilizability should be restored 

 upon addition of fertilizin. This test for the essentiality of fer- 

 tilizin has been attempted by a number of workers (see Tyler, 

 1948a for thorough review of this work). Fertilizin cannot be 

 demonstrated in washings from acid-treated, jellyless eggs. Never- 

 theless such eggs can be fertilized. Clearly then, fertilizin is not 

 essential for fertilization or the extraction procedure fails to re- 

 move all the fertilizin. In support of the latter view Frank ( 1939 ) 

 and Tyler ( 1941 ) have shown that jellyless eggs agglutinate when 



