PHYSIOLOGY OF THE SPERMATOZOON 125 



species; we do not indeed know how widespread the 

 phenomenon may be. Where it occurs we have a 

 definite indicator of a reaction; the failure of the indi- 

 cator in certain species is no evidence of lack of such 

 reaction, for the fundamental reaction is on the individ- 

 ual spermatozoon; the agglutination is a consequence 

 of secondary conditions such as the concentration 

 of the sperm suspension, the rate of movement of the 

 affected cells, and the composition of the medium; it 

 may also be that the reaction in certain species does 

 not involve such physical alteration of the sperm proto- 

 plasm as to permit of agglutination to one another. 

 We must therefore, I believe, utilize such positive indi- 

 cations as we have in our analysis, leaving the negative 

 cases for future investigation. 



The fertilization reaction proper is considered in chap- 

 ter vii. It is obvious that for the purposes of this reac- 

 tion, which involves adhesion and ultimate fusion of the 

 gametes, activation of the spermatozoon, tendency to 

 collect in the region of egg secretions, the thigmotropic 

 reaction, and the development of an adhesive surface 

 by action of the agglutinating substance of the egg 

 constitute forms of behavior exactly suited to the final 

 accomplishment. The layer of jelly that invests the 

 ova of most marine forms acts mechanically to entangle 

 the spermatozoa, and it also concentrates the action 

 of the egg secretions, with which it is heavily charged. 



The meeting of the egg and the spermatozoon is 

 to be regarded neither as a matter of random activity 

 of the spermatozoon alone, as some have been inclined 

 to regard it, nor yet exclusively as a result of direct 

 orientation of the spermatozoon toward the egg by 



