4OO E. E. JUST. 



the egg nucleus. Optimum localization is enhanced by complete 

 cortical reaction and by exposure to the agent beyond that suffi- 

 cient for cortical change. (See R. S. Lillie, effect of butyric acid 

 or heat on starfish eggs ; Miss Allyn, effect of heat on Chcrtop- 

 tcnts eggs; hypertonic sea- water on urchin eggs as in this paper.) 

 Instead of the superficial cytolysis-corrective factor theory of 

 experimental parthenogenesis I suggest that the activating agent 

 binds fertilizin, thus leading to complete cortical change. This 

 complete cortical change makes it possible that the additional 

 action of the agent brings about an optimum concentration of 

 aster-forming substance around the egg nucleus. The" nucleus 

 swells, a bipolar spindle forms, and development begins. 



LITERATURE CITED. 

 Just, E. E. 



'15 Initiation of Development in Nereis. BIOL. BULL., XXVIII., 93. 



The Fertilization Reaction in Echinarachnins Parma II. The Role of 



Fertilizin in Straight and Cross-Fertilization. BIOL. BULL., XXXVI., 



/ 

 1 1. 



The Fertilization Reaction in Echinarachnius Parma III. The Nature 

 of Butyric Acid Activation. Ibid., p. 39. 



'20 The Fertilization-Reaction in Echinarachnius Parma, IV. A Further 

 Analysis of the Nature of Butyric Acid Activation. BIOL. BULL., 

 XXXIX. 

 Lillie, F. R. 



'14 Studies of Fertilization, VI. The Mechanism of Fertilization in Ar- 



bacia. Jour. Exp. Zoo!., XIV., 515. 



*2ia Studies of Fertilization, VIII. On the measure of Specificity in Fer- 

 tilization between two Associated Species of the Sea-urchin Genus 

 Strongylocentrotus. BIOL. BULL., XL. 



'2ib Studies of Fertilization. IX. On the Question of Superposition of 

 Fertilization on Parthenogenesis in Strongylocentrotus purpuraius. 

 BIOL. BULL., XL. 

 Loeb, J. 



Artificial Parthenogenesis and Fertilization. University of Chicago 



Press, 1913- 

 Moore, C. R. 



'16 On the Superposition of Fertilization and Artificial Parthenogenesis. 



BIOL. BULL,, XXXI., 137. 



'17 On the Capacity for Fertilization after Initiation of Development. 

 Ibid., XXXIII., 258. 



