Vol. XL. January, 1921 No. i. 



BIOLOGICAL BULLETIN 



AUTHOR S ABSTRACT OF THIS PAPER ISSUED 

 BY THE BIBLIOGRAPHIC SERVICE, FEBRUARY 7 



STUDIES OF FERTILIZATION. 



VIII. ON THE MEASURE OF SPECIFICITY IN FERTILIZATION 

 BETWEEN Two ASSOCIATED SPECIES OF THE SEA-URCHIN 



GENUS STRONGYLOCENTROTUS. 1 



FRANK R. LILLIE, 

 UNIVERSITY OF CHICAGO. 



CONTENTS. 



I. Introduction i 



II. Comparison of the Gametes 3 



III. Cross-fertilization. 



1. General 3 



2. Variability of different individual cross-fertilizations 7 



(a) Purpuratus eggs fertilized by franciscanus sperm 7 



(&) Franciscanus eggs fertilized by purpuratus sperm 8 



3. The effect of sperm concentration 8 



(a) Purpuratus X franciscanus <$ 8 



(fc) Franciscanus X purpuratus $ p 



4. The measure of specificity 10 



5. Fertilization with mixtures of eggs and sperm 13 



IV. Cross-agglutination 14 



V. General 20 



I. INTRODUCTION. 



In previous studies on fertilization the writer has maintained 

 that the substance from eggs that agglutinates spermatozoa of the 

 same species is necessary for fertilization; more specifically that 

 the activating effect of the spermatozoon in fertilization is pri- 

 marily on this substance, which then sets the other processes in 

 operation. The agglutinating substance was accordingly called 



1 The writer wishes to express his indebtedness to J. Nelson Gowanlock for 

 his devoted and careful work as assistant in these experiments and in those 

 of study IX. T 



