SPERM AGGLUTINATION AND FERTILIZATION. 21 



with Other strands and form a net-work and the movements of 

 the spermatozoa soon cease. 



The substances of egg secretions, which I have hitherto called 

 hetero-agglutinins, belong to this category, in some cases at 

 any rate. Though I will not assert that there is no such sub- 

 stance as a hetero-agglutinin in the real sense of agglutination,, 

 yet the substance in Arbacia blood, or egg secretions, the effects 

 of which on Nereis sperm I have previously studied, should be 

 regarded as a toxic rather than an agglutinating substance, 

 having the mass coagulant action. As I stated in my last paper, 

 p. 541, it produces a permanent coagulum in Nereis sperm sus- 

 pensions; "in this respect the action differs from the iso-agglu- 

 tination, which is without toxic effects." 



We must keep firmly in mind the distinctions between aggre- 

 gation (tropisms) agglutination, and mass-coagulation. Agglu- 

 tination, with which we are particularly concerned, is distin- 

 guished from aggregation by the facts that it occurs in the 

 absence of a gradient, it involves physical adhesion, and cannot 

 be repeated if the reaction is once complete ; it also is characterized 

 by a high degree of specificity.^ From mass coagulation it is 

 distinguished by the facts (i) that it is non-toxic, (2) reversible, 

 (3) dependent on motility of the spermatozoa. Agglutination 

 occurs so far as I have observed with certainty only in response 

 to egg-secretions of the same species. 



For description of the phenomena of agglutination of sperm 

 by egg-extractives of the same species, I must refer to my previous 

 paper (Lillie, 1913a) ; the phenomenon in Arbacia is a true agglu- 

 tination in the sense defined, not a tropistic reaction, nor yet a 

 mass coagulation. Loeb has admitted this for Arbacia, and I 

 would therefore venture to suggest the probability that the phe- 

 nomenon which Loeb has described in Strongylocentrotus and 

 termed "cluster formation," which he interprets with some 

 reserve as a possible tropistic reaction, is also true agglutination, 

 which differs only quantitatively from Arbacia and Nereis. The 



1 Loeb admits that the "cluster formation" exhibits a high degree of specific- 

 ity. It is therefore inconsistent to interpret the reaction, as he also does, as a 

 "possible tropistic phenomenon" because such phenomena so far as we know do 

 not exhibit specificities of this kind. Agglutination phenomena, on the other 

 hand, as is well known, commonly exhibit equal specificity of a similar kind. 



