FERTILIZATION REACTION IN ECHINARACHNIUS PARMA. 33 



(e) Microscopic Appearance of Echinarachnius Sperm Aggluti- 

 nated by Arbacia Egg-water. Finally, it may be noted that the 

 microscopic appearance of Echinarachnius sperm agglutination 

 by Arbacia egg- water is markedly different from agglutination 

 by Echinarachnius egg-water. On this point I am borne out 

 by four investigators who were good enough from time to time 

 to observe the phenomena. In every instance they declared 

 that they could note a difference in the character of the aggluti- 

 nation. When Echinarachnius egg- water is blown into a drop 

 of Echinarachnius sperm suspension, the agglutination is sharply 

 defined because after the initial activation the spermatozoa 

 clump, leaving spaces between the clumps practictically free of 

 sperm. After a time, 'depending upon the strength of the egg- 

 water the clumps break up, the individual sperm being again 

 homogeneously distributed throughout the field. With Arbacia 

 egg-water the sperm of Echinarachnius behave differently. 

 The agglutinated masses tend to string out with some free sperm 

 among them. The agglutination is slower in beginning and 

 with strong egg-water slow in breaking up, indeed may never 

 break up, the agglutination being permanent. The whole 

 picture suggests a coagulative effect. Agglutination of Echi- 

 narachnius sperm by Arbacia egg- water probably is much like 

 that of Nereis sperm by Arbacia; this point I attempted to de- 

 termine but could not succeed in getting Nereis sperm at the 

 proper time. 



The evidence here presented shows that the iso-agglutinin 

 and hetero-agglutinin found in Arbacia egg- water are separate. 

 What the source is, one can scarcely say, although it may well 

 be the blood. Suspensions of eggs thoroughly washed free of 

 perivisceral fluid would, therefore, fail to charge sea-water with 

 the hetero-agglutinin, while the eggs would continue actively 

 to produce the iso-agglutinin. Whatever, the source of the 

 substance, the experiments cited above indicate that it is distinct 

 from the iso-agglutinin and is of the nature of a toxic substance. 



C. Summary of Part III. 



Summarizing we find (i) that cross fertilization between 

 Echinarachnius and Arbacia is possible but that the Arbacia egg 



