AGGLUTINATION OF SPERMATOZOA. 277 



spermatozoa in animals kept in the laboratory. Blood taken from 

 fresh animals, however, retains its hetero-agglutinating power for 

 at least three days. 



With blood, as with solutions of cytolyzed spermatozoa, there is 

 a disproportionate loss of agglutinating power with dilution. 



C. Effect of the Egg-Water of S. purpuratus and of S. francis- 



canus. 



The egg-water of ripe ova of 5". purpuratus and of 5". francis- 

 canus failed repeatedly to produce either activation or hetero- 

 agglutination of the spermatozoa of K. tunicata. Considering 

 that the latter can be intensely activated and agglutinated by blood 

 and by solutions of cytolyzed spermatozoa of these two species of 

 sea-urchins, and in view of the striking resemblance of iso-aggluti- 

 nation and hetero-agglutination in K. tunicata, it is especially 

 significant that the egg-water of both species of Strongyloccntrotus 

 fails to produce hetero-agglutination of K. tunicata spermatozoa. 

 This constitutes further evidence of the specificity of the iso- 

 agglutinating substance present in egg- waters. 



D. Changes in Spermatozoa Produced by Hetero-agglutinating 



Substances. 



In solutions which produce hetero-agglutination the heads of 

 the spermatozoa of K. tunicata become swollen at the base, as 

 indicated in Fig. I. 



A comparison of the dimensions of spermatozoa in sea-water 

 and in hetero-agglutinating solutions will illustrate this: 



Hetero-agglutinating 

 Spermatozoa. Sea-water. Solution. 



Head length IO/A lOjti 



Head width at base 2 p 2.25 to 3.35 /x, 



E. Discussion. 



Hetero-agglutinating substances have previously been demon- 

 strated in blood and in egg-water. Just and Lillie have suggested 

 that in the case of Arbacia the hetero-active substance is a con- 

 stituent of the blood, and that egg-water used was contaminated 



