PHYSIOLOGY OF THE SPERMATOZOON 109 



to distinguish between egg secretions and egg extracts; 

 we shall understand by secretions the normal exudates 

 of the egg in the medium in which insemination takes 

 place, and by extracts the water-soluble substances 

 that may be derived from the egg by crushing or plas- 

 molysis in an aqueous medium. It is obvious that the 

 extracts will contain more substances than the secretion, 

 and different kinds. 



In the first place it is known that the eggs of marine 

 animals give off CO 2 into the sea-water before fertili- 

 zation. But in addition to CO 2 other substances of 

 complex composition are given off; these are known 

 mainly by their effects on spermatozoa. Four such 

 effects may be noted in the case of the egg secretions of 

 Arbacia and Nereis and some other forms, viz.: (i) acti- 

 vation: the spermatozoa are stimulated to increased 

 activity, which is naturally followed sooner or later by 

 a state of rest; (2) aggregation: the spermatozoa are 

 aggregated; (3) agglutination: the spermatozoa be- 

 come stuck together in temporary clumps. (The first 

 three effects are noted on sperm suspensions of the same 

 species.) (4) The fourth effect is noted only on some, 

 but by no means all, foreign sperm suspensions; it is 

 a toxic effect, which is evidenced by irreversible agglu- 

 tination and destruction of the foreign spermatozoa. 

 The spermatozoa of Nereis for instance are thus de- 

 stroyed by the egg secretion of Arbacia, but the effect 

 is not reciprocal. It is possible that the last effect is 

 produced, not by an egg secretion proper, but by blood 

 carried over into the egg suspension. 



It does not necessarily follow that there are four 

 substances concerned in these biological reactions, but 



