AUTO-PARTHENOGENESIS IN ARBACIA AND ASTERIAS. 407 



there is no evidence. Moreover the substances demonstrated 

 by F. R. Lillie, seem to me sufficient to account for the normal 

 fertilization block if \ve make a much simpler assumption one 

 indeed which appears necessary on chemical grounds. 



The ovum, according to Lillie, contains egg-receptors, fertilizin, 

 and antifertilizin. Chemical affinities exist between the anti- 

 fertilizin and the spermophile groups as well as between the 

 receptors and the ovophile groups. Although Lillie does not 

 postulate a reaction involving these elements in the unfertilized 

 egg, it is difficult to believe that three substances, demonstrably 

 capable of uniting in the manner indicated, would lie side by side 

 without entering into combination, however loose. If this 

 assumption prove valid, we can consider this union as constituting 

 the normal fertilization block ("resistance," "obstacle") of the 

 unfertilized egg. 



From this standpoint it appears possible to explain the block 

 to parthenogenesis in washed eggs. The egg surface prior to 

 fertilization or treatment with parthenogenetic agents, is per- 

 fectly permeable to fertilizin. Lillie has shown, however, that 

 the anti-fertilizin can only be removed by destruction of the ova, 

 whose surfaces, with respect to these two substances, appear to 

 act like dialysers. It is quite likely therefore that w r ashed eggs 

 differ from unwashed by a relatively higher concentration of 

 anti-fertilizin. If now fertilizin is permitted to diffuse into a 

 washed egg, it would be bound by the anti-fertilizin and so an 

 initiatory effect, due to its further union (if indeed this occurs 1 ) 

 with the egg-receptors would be prevented. According to Lillie 's 

 view and the law of mass action, auto-parthenogenesis might 

 occur in washed eggs when the concentration of fertilizin is more 

 than enough to bind the anti-fertilizin. That it takes about 

 two hours to initiate auto-parthenogenesis, and that I failed to 

 initiate it in that length of time in washed ova, are both in 

 harmony with the above suggestion. 



So far as I can see, this is the only way at present, in which it 

 seems possible to draw a picture in which all the facts and all 

 the cases may find a place. It follows from the preceding reason- 



1 The avidity of fertilizin bound by sperm for the egg-receptors is assumed by 

 Lillie to be greater than in unbound fertilizin. The opposite effect, resulting from a 

 union of the spermophile groups with the anti-fertilizin is not excluded. 



