30 FRANK R. LILLIE. 



I cannot accept this statement of the problem, I have nevertheless 

 taken into consideration the fundamental fact, to which Loeb 

 alludes, in the full account of my experiments, which appeared 

 after Loeb's paper was in press. The fundamental fact is simply 

 that the fertilization process in some cases can be divided in 

 two sharply marked stages. This is perhaps most simply and 

 convincingly shown by my own experiment (Lillie, 191 1) of 

 removing the spermatozoon from the egg of Nereis after it had 

 already induced the cortical changes, with the result that the 

 developmental phenomena came to a standstill before the first 

 cleavage. I cannot agree with Loeb that the second stage in- 

 volves a factor corrective of an excess action of the factor of the 

 first stage. I think it is probable that we have a progressive 

 process readily capable of resolution into two stages. 



In my complete paper (Lillie, 1914) I considered the second 

 phase of fertilization with reference to the new theory, and may 

 refer the reader to the discussion there given (study VI, pp. 

 582-584). Here it is only necessary to point out that the 

 "fertilizin" theory is at least as well adapted to account for the 

 two stages as the "lysin" theory. 



4. Conclusion. 



I may be allowed to emphasize the essential features of my 

 theory with some added light thrown by the work of this summer. 

 The fundamental conception is that all agencies initiating 

 development of the egg do so by the same means, viz., activation 

 of an ovogenous substance, which I have termed fertilizin. This 

 conception brings fertilization and parthenogenesis under one 

 conception. I further assumed that such activation in the case 

 of fertilization was caused by union of a constituent substance 

 of the spermatozoon (the sperm receptors) with the fertilizin, 

 and that the activation expressed itself by consequent union of 

 the fertilizin with certain egg substances (the egg receptors). 

 The reaction was thus conceived in terms of the Ehrlich side- 

 chain theory, and was represented diagrammatically accordingly. 



That certain chemical combinations form an essential feature 

 of the fertilization reaction cannot be open to doubt. I have 

 not previously taken into account the consideration that the 



