38 EGG AND SPERM SUBSTANCES 



tilizin should combine with sperm even though it fails to aggluti- 

 nate. Tyler (1941) detected such combination in Urechis caupo 

 and Patiria niiniata by the inhibiting action of fertilizin on the 

 fertilizing power of the sperm. Mactra (Spisula) solidissima fer- 

 tilizin was first detected by the same method (Metz and Dono- 

 van, 1949). The second method involves the conversion of the 

 normally nonagglutinating system to an agglutinating one by the 

 addition of an adjuvant. The presence of fertilizin in Patiria egg 

 water, originally demonstrated by the first method, was subse- 

 quently confirmed by this second method. Later studies employ- 

 ing the adjuvant technique have demonstrated agglutinating 

 fertilizins in egg waters of nine other asteroids (see section on 

 starfish agglutination). Finally calcium appears to be necessary 

 for agglutination in some (Loeb, 1915; Vasseur, 1949a) but not 

 all (Dan, 1954b) species. Fortification of the system with an 

 excess of this ion may enhance agglutination (Vasseur, 1949a) 

 or even induce agglutination in nonagglutinating systems. In a 

 number of forms (see effects on sperm morphology, above) egg 

 water has been shown to induce the sperm acrosome reaction. 

 Although it is premature to conclude that fertilizin is the re- 

 sponsible agent in this effect, it is possible that such may prove to 

 be the case and that the acrosome reaction can be developed into 

 a sensitive test for fertilizin. 



As suggested by the above account, failure to obtain agglutina- 

 tion may result from several causes. In some cases this may be 

 due to a high calcium requirement. In the starfish, metal ions 

 prevent agglutination by blocking most of the antifertilizin 

 gi'oups of the sperm. In some species fertilizin may exist mainly or 

 entirely in the univalent form (Tyler, 1941, 1948a). Finally, fer- 

 tilizin or fertilizin-like material may occur in an insoluble form, 

 firmly bound to or built into the egg surface. The mating type 

 substances of Paramecium are of this nature ( Metz, 1954a ) . Like- 

 wise sea urchin eggs appear to retain a bound layer of fertilizin 

 at their surfaces after the outer gelatinous coat has been removed 

 by acid treatment or enzymatic digestion (Tyler, 1941; Tyler and 

 Metz, 1955). As Tyler (1948a) suggests, the normally jellyless 



