SPERM AGGLUTINATION AND FERTILIZATION. 23 



are there arrested. The proof of this interpretation is found in 

 the fact that, if increasing concentrations of CO 2 are used, the 

 ring forms outside the drop and becomes progressively wider, 

 i. e., the migration ceases at a distance from the center which 

 increases with CO2 or acid concentration (see 1913a, pp. 536-538). 

 Loeb suggests that the ring formation with a clear external zone 

 around it is "an indication that the spermatozoa are negatively 

 chemotropic to the strong egg-sea-water, and possibly positively 

 chemotropic to the more diluted egg-sea-water, or to the dense 

 collection of spermatozoa in the ring." The latter suggestion is 

 of course untenable as a primary cause, for the ring-formation is 

 precisely the phenomenon to be explained. It is also unnecessary 

 to assume any negative tropism; the ring formation is due to a 

 limitation of the positive movement by concentration. This is 

 fully discussed in the paper referred to above, but Loeb does not 

 allude to the discussion. 



2. The Source of the Agglutinating Substance. 



Professor Loeb has also taken issue with me on the question 

 of the origin of the agglutinating substance. He regards his 

 experiments as proving that the substance which causes the 

 "cluster formation" is not formed in the egg but in the chorion; 

 i. e., in the layer of jelly which surrounds the egg. On the other 

 hand I regarded it (and still hold to the opinion) as a secretion 

 of the egg; with which the jelly of course becomes saturated.^ 

 Loeb's observations again were on Strongylocentrotus and mine 

 on Arbacia. The issue is a real one even though the chorion is 

 itself a secretion of the egg in earlier stages. 



Loeb's conclusion was based on his observation that if the 

 chorion be dissolved off in dilute hydrochloric acid in sea-water, 

 the naked eggs transferred to sea-water produce no detectable 

 amounts of the agglutinating substance any more, whereas the 

 acid sea-water contains it in large quantities. My conclusions 

 were based on the observation that when eggs of Arbacia are 

 deprived of jelly (chorion) by shaking, or a prolonged series of 



1 Glaser (1914) also agrees substantially with me: "the agglutinating substance 

 is located in greatest abundance in the jelly and the eggs also contain this material," 

 P- 371- 



