132 JACQUES LOEB 



was possible probably on account of the fact that the sperma- 

 tozoa became immobile. 



These and other experiments prove that an increase in the 

 alkalinity of the solution shortens the duration of the clusters; 

 in spite of the fact that an increase in alkalinity of the sea water 

 favors the real agglutination of sperm. 



The writer tried then to ascertain which salt solutions favor the 

 formation of these clusters. To investigate this point the ovaries 

 and testes of purpuratus were washed in an m/2 NaCl solution 

 and then put directly into another m/2 NaCl solution without 

 coming in contact with sea water. It was found that the super- 

 natant solution of the eggs did never, or only exceptionally, give 

 rise to cluster formation with the NaCl sea water; the reason for 

 this may be partly the fact that the spermatozoa are practically 

 inactive in a pure NaCl solution and that although the presence 

 of the supernatant NaCl solution from the eggs stimulates the 

 spermatozoa into activity this may not always be sufficient. The 

 addition of KCl does not materially improve the cluster forma- 

 tion, the addition of the chlorides of Mg, Ca, Sr and Ba and of 

 MgS04 vastly increases the cluster formation or induces it in an 

 otherwise inefficient NaCl solution. 



It is not possible to draw any conclusions from these facts upon 

 the nature of the process underlying it. 



THE ORIGIN OF THE SUBSTANCE CAUSING THE CLUSTER 

 FORMATION 



Lillie assumes that the substance which causes the phenomenon 

 described by him as agglutination is given off by the egg itself 

 though he states that the jelly which surrounds the egg — viz., the 

 chorion — is saturated with this substance. The writer was 

 curious to know whether the phenomenon of cluster formation 

 depends upon a substance given off by the egg or whether it is due 

 to a substance originating from the chorion. It could easily be 

 shown tjhat the latter is the case. Herbst had stated that the 

 chorion of the sea urchin egg can be dissolved by acid. The 

 writer therefore put a mass of eggs of purpuratus for three minutes 



