Gametogenesis, Fertilization and Parthenogenesis 



187 



ing groups available to unite separate cells. 

 Univalent molecules would combine with 

 the separate cells and be incapable of tying 

 them together. 



Some svipport for the above interpretation 

 of the spontaneous reversal of agglutination 

 in sea urchins is obtained from experiments 



apparent absence of fertilizin in many spe- 

 cies of animals. It is known that the egg 

 waters of many species of animals, such as 

 the abalone and Cumingia (Sampson, '22), 

 Urechis (Tyler, '41), some starfish (Metz, 

 '45) and even certain sea urchins (Vasseur 

 and Hagstrom, '46) fail to agglutinate the 



I'. 





Fig. 58. Photomicrographs of sperm of Megathura crenulata, X 260. a, b, and c. Show union by heads and 

 by end pieces of tails in strong, moderate and weak fertilizin solutions, respectively, d and e, Show head ag- 

 gregates originally present in sperm suspension. (From Tyler, '40a.) 



in which the ordinary agglutinin is con- 

 verted into a nonagglutinating (univalent) 

 form by the action of heat, proteolytic en- 

 zymes, ultraviolet or x-radiation (Tyler, '41, 

 '42; Metz, '42a, b). Treatment of the sperm 

 with such univalent fertilizin inhibits their 

 agglutination by ordinary fertilizin and also 

 renders them nonfertilizing, without im- 

 pairing their motility. 



The concept of univalent antigen or anti- 

 body also provides an interpretation for the 



homologous spermatozoa. Such failure to 

 demonstrate fertilizin in all species of ani- 

 mals has been used as an argument against 

 considering fertilizin to have any general 

 significance for fertilization. However, that 

 the egg water of such nonagglutinating spe- 

 cies might contain a fertilizin-like substance 

 was indicated in experiments of Tyler ('41) 

 and clearly established by Metz ('45). The 

 latter worker was able to cause specific ag- 

 glutination of sperm, in species of starfish 



