STUDIES OF FERTILIZATION. 1 7 



females has, however, not the slightest effect on franciscanus 

 sperm, however concentrated it may be. (See Table VII., No. 

 6.) This is not at all unusual. The hetero-agglutinating action 

 is sporadic, while the iso-agglutinating action is constant. On 

 the assumption that the iso-agglutinating action is caused by a 

 single substance we cannot have this substance sometimes agglu- 

 tinating the sperm of franciscanus and sometimes not, unless we 

 assume that the variability is in the sperm of different individuals 

 of franciscanus. This cannot be the case, for the same sperm 

 suspension of franciscanus may show the apparent agglutination 

 with the egg-water of one individual of purpuratus and fail to 

 show it with another equally strong in isoagglutination. I have 

 also tried a non-heteroactive egg-water of purpuratus on the 

 sperm of different individuals of franciscanus and found it nega- 

 tive consistently. It must therefore follow that the egg-waters 

 of certain indivaduals of purpuratus contain a separate hetero- 

 active substance. 



This substance is apparently not a constituent of the normal 

 blood of purpuratus, for the blood of purpuratus seems to be as 

 indifferent a medium for the sperm of franciscanus as for the 

 sperm of purpuratus, and the reverse is also true. In this respect 

 it differs from the substance of Arbacia egg-water active on 

 Nereis and Echinarachnins. 



It should also be noted that the apparent hetero-agglutination 

 differs in two other important respects from either iso-agglutina- 

 tion, (i) in the appearance of the reaction, (2) in the relation 

 of duration of the reaction to dilution : 



In iso-agglutination round solid masses of agglutinated sperma- 

 tozoa form in a few seconds ; these are preceded by strand- 

 formations which rapidly contract, and the strands must be pre- 

 ceded by cloud formations which, however, condense so rapidly 

 to strands as to make positive observation of these exceedingly 

 difficult. This is true both with stronger and weaker solutions, 

 the difference consisting in the scale of the phenomena and the 

 rate of reversal. The action of purpuratus egg-water on fran- 

 ciscanus sperm never proceeds beyond the stage of dense clouds ; 

 it does not therefore resemble the action of more dilute egg- 



