SPERM AGGLUTINATION AND FERTILIZATION. 29 



Sperm does not reveal it; it may nevertheless be activated by 

 purpuratus sperm and this is the essential point in the theory.^ 

 Agglutination of sperm is of no significance except as indicator. 

 As I pointed out in my previous paper, binding of the fertilizin 

 by sperm receptors, i. e., the chemical reaction, is a thing entirely 

 distinct from agglutination ; if such binding causes a certain kind 

 of physical surface change of the spermatozoa of suspensions of a 

 certain minimum concentration, they agglutinate; otherwise not. 

 Agglutination is a valuable indicator that enables us to make 

 certain analyses, and that is all. The same principle of fer- 

 tilization may hold in the entire absence of sperm agglutination. 



Another objection in which Loeb supports the possibility of 

 superposing fertilization on parthenogenesis will be dealt with in 

 a separate paper. My contention in this case is that the possi- 

 bility of such superposition always rests upon incompleteness of 

 the parthenogenetic reaction; if the fertilization reaction be 

 complete, whether by parthenogenesis or insemination, it cannot 

 be repeated. Everybody ajimits that eggs fertilized by sperm 

 cannot be refer tilized ; it is a logical impossibility that eggs "fer- 

 tilized" by parthenogenetic reagents should be refertilized. The 

 problem of the apparent contradiction involved in Loeb's and 

 Herbst's contention of superposition works out in the manner 

 indicated. A study of this problem by one of my students will 

 appear soon. 



Loeb cites as a farther dififiiculty of my fertilizin theory, which 

 he says I have not considered, "that in addition to the membrane 

 forming substance still another, namely a correcting agency, is 

 necessary for causation of the development of the egg." Though 



^ Loeb states (1914. P- i35): "If the phenomenon of cluster formation were in- 

 separably associated with the power of the eggs of being fertilized, we should expect 

 that sperm should only be able to fertilize the eggs of a species if the egg-sea-water 

 of the same species caused the cluster formation of the sperm." I have never 

 maintained that agglutination ("cluster formation") is inseparably associated with 

 the power of the eggs of being fertilized, but merely that a certain substance pio- 

 duced by the egg is a necessary factor in fertilization. In some cases this substance 

 (fertilizin) produces agglutination of the sperm of its own species, and this reaction 

 furnishes an indicator of its amount, when present, or of its absence. In other 

 cases such an indicator is lacking: I do not find that supernatant sea-water of the 

 eggs of the starfish (Asteria forbesii), for instance, agglutinates its own sperm; but 

 I have evidence, to be published elsewhere, that the mechanism of fertilization 

 may be explained in the same way as in Arbacia. 



