EGG SECRETIONS OF ARBACIA AND ASTERIAS 479 



is the parthenogenetic portion of fertilizin which suggests a posi- 

 tive result — one indicative of a lipase. If the agglutinin is an 

 enzyme, its nature is not yet known. 



C. Concerning inhibitors 



The dual nature of the secretion in no wise impairs the utility 

 of inhibitors in the analysis of the fertilization reaction. An 

 inhibitor may function in a purely mechanical or physical manner 

 as b}^ making the egg membrane tough so that the sperm cannot 

 enter, or it may remove from the reaction system one or more of 

 the essential reagents. Such an inhibitor, as Lillie ('14) has 

 pointed out, may act by : 1) Removing fertilizin. 2) Occupying 

 the 'sperm receptors.' 3) Occupying the 'spermophile side- 

 chain' (agglutinin). 4) Occupying the 'ovophile side chain' 

 (lipolysin). 5) Occupying the 'egg receptors.' In other words, 

 an inhibitor may combine with the agglutinin, the lipolysin, or the 

 substances within the sperm or egg with which these react. We 

 shall consider for the present only inhibitors of organic origin. 



1. Removal of fertilizin. Repeated washing is the only method 

 yet devised for removing fertilizin. The discussion of the effects 

 of this treatment, page 464, shows it to be an effective means of 

 inhibition. 



2. Comhination with sperm receptors. Godlewski ('10) found 

 that sea-urchin eggs to which had been added Chaetopterus 

 sperm were made resistant to sperm of their own species subse- 

 quently added. Lillie interprets this as being due, perhaps, to a 

 change in the spermatozoa which prevents their union with ferti- 

 lizin. In other words, he believes that from Chaetopterus sperm 

 may be dissolved into the water some substance which combines 

 with the sea-urchin 'sperm receptor' and occupies the group 

 which would normally unite with the spermophile side chain of 

 fertilizin. The receptor so 'occupied' would be unable to com- 

 bine with the fertilizin-egg complex, and therefore fertilization 

 would not occur. This interpretation, Lillie admits, is purely 

 hypothetical. No experiments to test it have been performed. 

 It would be just as reasonable to assume that Chaetopterus 

 sperm combined with or adsorbed the agglutinin or the lipolysin 

 or that they in some way injured the egg itself. 



