AGGLUTINATION OF SPERMATOZOA. 271 



pensions of such spermatozoa I noticed an intermediate stage in 

 the process of agglutination. This intermediate stage occurs dur- 

 ing reversal. It is characterized by a radial orientation of the 

 active spermatozoa such that the swarm momentarily takes on the 

 appearance of a three-dimensional pin wheel. At the center of the 

 wheel is a " nucleus " of sperm heads with tails radiating outward, 

 while the periphery of the wheel is composed of a dense zone of 

 sperm heads with their tails radiating inward. In optical section 

 it is as though a set of spokes originating at the hub of a wheel 

 were dovetailed between another set radiating inward from the 

 rim. These pinwheels gradually break up and eventually the 

 spermatozoa are completely dispersed as in typical reversible 

 agglutination. This pinwheel formation is not comparable to a 

 secondary aggregation which often follows iso-agglutination. In 

 such aggregation the masses formed are irregular in shape; and 

 the spermatozoa composing them are not intensely active, not 

 oriented, and are readily dispersed by shaking. 



4. ISO-AGGLUTINATION IN Katharina tunic at a. 



The spermatozoa of K. tnnicata are inactive or but slightly 

 active in sea-water. They can be roused to intense activity by 

 foreign blood or foreign tissue extracts and exhibit a spiral method 

 of locomotion similar to that described for other types of sperma- 

 tozoa. In contact with surfaces they move anti-clockwise. This 

 is probably due to their structure. (See Fig. i.) As judged by 

 their activation by various substances the spermatozoa of this 

 species were ripe as early as April 9. Egg- water tested April 15, 

 May 2, and May 16 failed to produce even an activation of sperma- 

 tozoa. Inseminated eggs did not develop, indicating that the eggs 

 were not ripe. On May 27 secretions from ripe eggs of females 

 caught on the same day caused intense activation, aggregation, and 

 a peculiar type of agglutination. The latter is comparable to the 

 intermediate stage in the iso-agglutination reaction obtained with 

 stale spermatozoa of Arbacia. 



Following activation and aggregation of the spermatozoa into a 

 dense ring, the latter rapidly break up into three dimensional pin- 

 wheels instead of into the whirling swarms characteristic of the 

 iso-agglutination in sea-urchins and in Nereis. Within the in- 



