2 68 MYRA M. SAMPSON, 



report evidence is given for the first time of the occurrence of iso- 

 agglutination in the black chiton, Katharina tunicata, and of hetero- 

 agglutination between K. tunicata and 5. purpuratus, and between 

 K. tunicata and S. franciscanus, and the reciprocal hetero-aggluti- 

 nation between either S. purpuratus or 6". franciscanus and K. 

 tunicata. Similar reciprocal hetero-agglutination occurs between 

 either 5\ purpuratus or S. franciscanus and Ishnochiton inagda- 

 lenensis. 



The results embodied in this report were obtained in 1920-1921 

 at the Hopkins Marine Station of Leland Stanford University at 

 Pacific Grove and at the Marine Biological Laboratory at Woods 

 Hole. I wish to express here my appreciation of the hospitality 

 extended to investigators at the Hopkins Marine Station and my 

 thanks to the Director, Dr. W. K. Fisher, and to Dr. Gertrude 

 Van Wagenen, for their assistance and encouragement. The 

 photomicrographs accompanying this paper were taken for me by 

 Dr. Doane, of the Department of Entomology of Stanford Uni- 

 versity. For the use of a research room at Woods Hole I am 

 indebted to the Director, Dr. F. R. Lillie, and for suggestions and 

 criticisms to Dr. O. C. Glaser. 



II. ISO-AGGLUTINATION. 



i. GENERAL. 



Iso-agglutination is characterized by the rapid formation of 

 dense spherical swarms of intensely active adherent spermatozoa 

 and by the subsequent reversal of this process, Lillie (1921). 

 The duration of the reaction varies with the concentration and 

 freshness of the sperm suspension and of the egg-water, Lillie 

 (1914, 1915), and is obtained only with motile spermatozoa, Loeb 

 (1914). This reaction has been observed in a few marine animals 

 and wherever it occurs indicates that we are dealing with ripe 

 reproductive cells, species true. Its significance lies in its speci- 

 ficity, Lillie (1921). 



Iso-agglutination has been reported by Lillie (1912, 1913) for 

 Arbacia punctulata and for Nereis; by Glaser (1914) for Asterias 

 forbesii; and by Just (1919) for Echinarachnius. Loeb (1914) 

 described " cluster formation " in Strongylocentrotus purpuratus 



