42 EGG AND SPERM SUBSTANCES 



treated with antifertilizin from sperm. This result indicates that 

 some fertihzin remains bound to the egg surface. 



Similar results have been obtained following treatment of 

 Arbacia eggs with ciystalline trypsin and chymotrypsin (Tyler 

 and Metz, 1955). The digestion removes the egg jellies, but 

 these eggs fertilize when inseminated. Interpretation of the ac- 

 tion of the enzymes is complicated by the fact that the treated 

 eggs fail to elevate fertilization membranes upon fertilization. 

 This suggests that the enzymes digest not only the jelly but also 

 the vitelline membrane of the egg and any fertilizin bound to it, 

 including that remaining after acid sea water treatment. Even 

 though the vitelline membrane may be removed and in spite of 

 the fact that such eggs show a greater receptivity to foreign sperm 

 (Hultin, 1948a,b; Bohus Jensen, 1953a,b; Tyler and Metz, 1955), 

 they still agglutinate on addition of antifertilizin (Tyler and 

 Metz, 1955). If it is assumed that antifertilizin suffers no loss in 

 specificity upon extraction from the sperm, it must be concluded 

 that some fertilizin, possible cytofertilizin, resists the action of 

 trypsin for some time. 



Evidently, then, an unequivocal test of the fertilizability of 

 the fertilizin-free egg has yet to be devised. Nevertheless, removal 

 of the jelly by acid or enzymes lowers the fertilizability of eggs to 

 the extent that more sperm are required to obtain a given per- 

 centage of fertilized eggs. Furthermore, the fertilizability and 

 antifertilizin agglutinability decrease in parallel fashion upon 

 prolonged treatment with trypsin (Tyler and Metz, 1955). Fi- 

 nally, antifertilizin treatment greatly reduces the fertilizability of 

 both control and jellyless eggs (Tyler, 1941; Tyler and Metz, 

 1955 ) . These experiments, then, show quite clearly that fertilizin 

 in the form of the jelly layer aids fertilization. Furthermore, they 

 strongly suggest that fertilizin at the egg surface is essential for 

 fertilization. 



If fertilizin is an aid to or essential for fertilization, addition of 

 more fertilizin to eggs, especially jellyless eggs, might be expected 

 to improve fertilization. However, as Tyler ( 1941 ) points out, no 

 way has yet been found to cause added fertilizin to assume its 

 normal relationship ( a jelly layer ) to the egg. Furthermore, Mon- 



