568 FRANK R. LILLIE 



In a short time the egg develops a physiological condition in 

 which union of spermatozoa is no longer possible. The immediate 

 protection against supernumerary spermatozoa is, however, 

 afforded by the paralyzing action of the egg-secretion. 



Union of ovum and sperm, prevention of polyspermy, and the 

 attainment of a condition of insusceptibility to other spermatozoa 

 are phenomena so closely related in time sequence that a casual 

 connection must be postulated. These can be brought under 

 one head, in the case of Nereis at least, if we assume that the sub- 

 stance that paralyzes all tha sperm in the vicinity of the egg is 

 necessary for the actual fusion of the spermatozoon and egg and 

 is completely used up in the cortical changes that follow immedi- 

 ately on insemination: the condition of insusceptibility would be 

 due to loss of a necessary substance, the immediate prevention of 

 polyspermy to paralysis of all ineffective spermatozoa, and the 

 penetration of the sperm to a chemical change of the effective 

 sperm and the neighboring egg-cytoplasm involving physical alter- 

 ations in surface tension, viscosity, et cetera. 



In the case of Arbacia, I have been unable to demonstrate an 

 increase of secretion from the egg into the sea-water at the mo- 

 ment of insemination nor yet cessation of such secretion soon after 

 insemination; however, as indicated before (p. 560), this failure 

 may be due to the presence of unfertilized eggs in the experiments, 

 which require to be repeated. 



11. summary: part iv 



1. The ova of Nereis and Arbacia give off into the sea-water 

 a substance (or substances) which agglutinates the sperm of their 

 own species. The sea-water, which has the agglutinating substance 

 in it, has also a substance to which the spermatozoa of the same 

 species are positively chemotactic. 



2. The eggs alone produce the sperm agglutinating substance; 

 It cannot be extracted from other tissues. 



3. The agglutinin disappears from a mixture of sperm suspen- 

 sion and agglutinin if not present in excess; the disappearance is 

 attributed to chemical combination. 



