14 FRANK R. LILLIE. 



of equal parts of both kinds of sperm (2 drops dry sperm to 5 c.c. 

 of sea water in each case) was made one day at 11.58 A.M. and 

 was used to fertilize mixed eggs at 12.02 P.M., at 12.46, at 1.49, 

 at 2.43 P.M. and at 10.54 A.M. the next day. In the first fertil- 

 ization practically all eggs of both kinds fertilized ; in the second 

 fertilization about 55 per cent, of the franciscanus eggs fertilized 

 and 75 per cent, of the purpuratus; percentages were not esti- 

 mated in the third and fourth fertilizations, but there was little 

 if any falling off. In the last fertilization made about 23 hours 

 after mixing, using the same eggs and sperm there was practically 

 no fertilization. Controls consisting of the same mixed eggs 

 fertilized with the same sperm samples used in the experiment, 

 but unmixed, were run, showing approximately the same rate of 

 falling off as the mixed sperm, during the first day. There is 

 thus no evidence of any antagonism of sperm. On the second 

 day the unmixed franciscanus sperm fertilized about 15-20 per 

 cent, of the franciscanus eggs in the mixture, but the mixed 

 franciscanus sperm fertilized practically none. The purpuratus 

 eggs did not fertilize either with unmixed or mixed purpuratus 

 sperm. There is thus an indication that the franciscanus sperm 

 loses fertilizing power more rapidly in presence of purpuratus 

 sperm than when separate. 



IV. CROSS- AGGLUTINATION. 



In 1913 I described the phenomenon of agglutination of sperm 

 suspensions of Arbacia by the egg-water of the same species ; 

 the phenomenon is a reversible one, the duration of which depends 

 on the concentration of the egg-water. With stronger solutions 

 the. agglutinated masses are larger and last longer; with the 

 lowest effective dilution the masses are microscopic in size and 

 disperse in 5 or 6 seconds. It is possible by using a minimum 

 quantity of water to a large bulk of eggs to secure an egg-water 

 that will give the minimum reaction when diluted 1,200 times. 

 The phenomenon is associated with an intense activation of the 

 spermatozoa, due to a distinct substance, and is evidently caused 

 by a change in the heads of the spermatozoa that renders them 



