C. B. METZ 39 



eggs of many forms may prove to be comparable to jelly-free sea 

 urchin eggs with respect to fertilizin. 



It should be evident from the foregoing discussion that ferti- 

 lizin may exist in several fomis and that any one of a variety of 

 methods may be required to demonstrate it. Clearly then, the pos- 

 sibility that fertilizin, in one form or another, occurs widely or 

 universally among eggs cannot yet be rejected. 



Source of Fertilizin. Lillie (1914) believed that fertilizin was 

 produced continuously by Arbacia eggs. Loeb (1914, 1915), how- 

 ever, found that after dissolving the gelatinous coat in acidified 

 sea water no fertilizin could be obtained from sea urchin eggs. 

 This has been confirmed repeatedly (Tyler and Fox, 1939, 1940; 

 Tyler, 1940a; Hartmann, Schartau, and Wallenfels, 1940; see also 

 Runnstrom, 1949a; Tyler, 1948a). In fact fertilizin appears to be 

 the sole component of the jelly for Tyler ( 1949 ) and Runnstrom, 

 Tiselius, and Vasseur ( 1942 ) found that solutions of the coat are 

 homogeneous upon electrophoretic or ultacentrifugal analysis. 



Although identification of fertilizin with the jelly layer of sea 

 urchin eggs is well established, the cellular origin of the jelly is 

 disputed. For example, on the basis of histological studies Jenkin- 

 son (1911) believed that the jelly is layed down by the follicle 

 cells of the ovary, whereas Lindahl (1932) concluded that the 

 egg itself produces the jelly. Later Vasseur (1951) obtained fer- 

 tilizin from the ovaries of spent sea urchins. Since these ovaries 

 lacked eggs, Vasseur concluded that the fertilizin was produced 

 by ovarian tissue, not by eggs. However, fertilizin from eggs may 

 have remained in the ovary after the eggs were shed. 



In this connection it is of interest that Mellita quinquiesper- 

 forata egg suspensions obtained by the KCl injection method 

 frequently contain jellies which do not enclose eggs. Indeed, over 

 90% of jellies from some females are empty (Metz, unpub- 

 lished ) . These empty jellies may have been laid down independ- 

 ently by ovarian tissue in the absence of eggs, or the eggs may 

 have escaped from the jellies. The former possibility seems more 

 likely since the suspensions do not contain proportionate numbers 

 of naked eggs. Nevertheless, in the writer's opinion definite con- 



