C. B. METZ 59 



The agent inhibits the sperm agghitinating action of fertihzin 

 (presumably in the absence of antifertiHzin ) and fertiHzation. 

 The latter action is reversible to the extent that eggs washed free 

 of the extract will fertilize although development is abnormal 

 (Runnstrom, 1947). Runnstrom and co-workers suggest a num- 

 ber of possible functions for the agent in fertilization. However, 

 judgment as to the function of the agent should be withheld 

 pending further study. 



Summary 



It is evident from the account given here that fertilization and 

 especially the activation of the egg cannot as yet be described 

 completely in terms of the interaction of known specific egg and 

 sperm substances. However, it is equally clear that agents are 

 known which have specific action upon gametes of the opposite 

 sex. Of these the egg membrane lysins from sperm perfomi a def- 

 inite, and essential, though secondary, function in fertilization, 

 namely, removal of mechanical barriers between the approaching 

 sperm and the egg surface. Agents from eggs would also appear 

 to facilitate fertilization by physiological action on sperm. In- 

 crease in sperm motility is one of the more obvious of these effects. 

 Fertilizin and antifertilizin on the surfaces of the respective gam- 

 etes may well be the receptor agents by which sperm and eggs 

 make initial union. Furthermore, the presence of these substances 

 on the gametes and not on other tissues can account for the tissue 

 specificity of fertilization. Likewise, the species specificity of fer- 

 tilization may be attributed largely, if not entirely, to these agents, 

 since action of fertilizin on sperm parallels roughly the species 

 specificity of fertilization. Positive evidence for a direct and es- 

 sential role of known substances in the primary activation reac- 

 tions is wanting. On the other hand, the possibility of such action, 

 especially for fertilizin and antifertilizin is not excluded by the 

 available evidence. It remains to discover the role that known 

 agents (especially fertilizin and antifertilizin) play in the activa- 

 tion of the egg and perhaps to discover other agents which are as 

 yet unknown and unsuspected. 



