2 7 8 



MYRA M. SAMPSON. 



with blood. The hetero-active substance in the egg- water of 5. 

 purpuratus for S. franciscanus is, however, not a normal con- 

 stituent of the blood of S. purpuratus, Lillie, 1921. It is improb- 

 able that contamination with blood can account for the strong 



V / 



FIG. i. Spermatozoa of Katharina tunicata. 



a. In sea-water normal. Mag. x 5,000 (approx.). 



b. In solution of cytolyzed spermatozoa of S. purpuratus. The heads are 

 swollen at the base. Mag. x 5,000. 



hetero-agglutinating power of the solutions of cytolyzed sperm 

 made from 5 per cent, suspensions of spermatozoa. Such a dilu- 

 tion of whole blood would have slight hetero-agglutinating prop- 

 erties. 



It is possible that the products of cytolysis of eggs or of tissue 

 cells of these two species of sea-urchins would also cause hetero- 

 agglutination of spermatozoa of K. tunicata. 



