C. B. METZ 43 



roy et al. ( 1954 ) have shown that f ertihzm in solution and in the 

 gel form have somewhat different chemical as well as physical 

 properties. Finally, fertilizin in concentrated solution can act 

 upon and saturate the sperm while the latter is still distant from 

 the egg (see below). In view of these considerations it is not sur- 

 prising that addition of fertilizin fails to increase the fertilizability 

 of eggs, even jellyless eggs (Tyler, 1941). 



Effect of Fertilizin on the Fertilizing Capacity of Sperm. In 

 the sea urchin, sperm agglutination spontaneously reverses. If 

 the sperm is initially treated with an excess of fertilizin, the "re- 

 versed" sperm fail to reagglutinate on further addition of ferti- 

 lizin. This indicates that the surface antifertilizin of the spemi is 

 bound or blocked by univalent fertilizin ( Fig. 1 ) . Such saturation 

 of the surface might be expected to have a profound eflPect upon 

 the fertilizing capacity of the sperm. However, it should be noted 

 at the outset that tests of the fertilizability of reversed sperm are 

 critical only if the sperm surface antifertilizin is completely 

 blocked or unless an elaborate quantitative measurement of 

 sperm fertilizability is performed. With this factor controlled 

 Tyler ( 1941 ) found a marked reduction in fertilizing capacity 

 of reversed S. purpuratus sperm. Similarly, reduction in fertilizing 

 power has been reported in some other sea urchins (e.g., Dan, 

 1954b). On the other hand, a number of investigators have ob- 

 tained no significant reduction in fertilizing capacity of fertilizin- 

 treated sperm of other species (e.g., Fuchs, 1914, 1915; Hagstrom, 

 1956; Runnstrom, 1949a). Most of these reports failed to take 

 into account the degree of saturation of the sperm with fertilizin. 

 Finally, in studies of several fornis (Metz, 1942b; Metz and 

 Donovan, 1949; Tyler and Metz, 1955), species differences were 

 found. In Mactra (Spistila) solidissima, and S. purpuratus, fer- 

 tilizin treatment markedly reduced the fertilizing capacity of the 

 sperm, but it failed to do so in Arhacia punctulata* and Mellita 

 quinquiespeiiorata. However, these species differences appear to 

 be relative, not absolute, for Tyler and Metz ( 1955 ) did find a 

 reduction in fertilizing capacity when the reversed sperm of 



* Lillie (1913b) reported reduction of fertilizing capacity of Arhacia 

 sperm after fertilizin treatment. 



