342 HOMER W. SMITH AND G. H. A. CLOWES. 



does not actually introduce some abnormality into this initial event, 

 it impairs subsequent events of the fertilization process to such a 

 degree as to prevent normal development. There is apparently no 

 reversible block created by alkali corresponding to that created 

 by acid, where the fertilization reaction proceeds in an all-or-none 

 fashion. This conclusion is supported by the extremely rapid in- 

 jury of the eggs and sperm if separately exposed to the alkaline 

 solutions (pH 10.0), which prevent normal fertilization, and the 

 complete absence of such injury in acid solutions (pH 6.8 to 7.0) 

 which have a similar effect. 



POLYSPERMY. 



In the case of Arbacia eggs there is a very narrow range in H- 

 ion concentration in which the incidence of polyspermy is un- 

 usually high. This range is approximately defined in Figure I 

 by the heavily shaded portion ; the maximum of polyspermy is 

 close to pH 7.2. Though the incidence of polyspermy at all H-ion 

 concentrations increases with increasing age or staleing of the 

 eggs, yet within this narrow range, centering at pH 7.2, practically 

 all the eggs will be polyspermic even when they are fresh and 

 when the incidence of polyspermy is nearly zero from pH 7.4 to 

 9.8. 



In Asterias, polyspermy shows no marked maximum at any H- 

 ion concentration but occurs more or less uniformly from pH 8.5 

 to 9.5 (Fig. 2). When excessive quantities of sperm are used in 

 insemination, nearly all the eggs may be polyspermic from 8.15 to 

 9.6. It is perhaps significant that the polyspermy curve, even 

 though extremely broad, is limited on the alkaline side ; for the 

 incidence of polyspermy decreases appreciably before the alkalin- 

 ity is sufficient to inhibit fertilization, indicating that in its gen- 

 eral nature the underlying mechanism in Asterias is similar to that 

 in Arbacia. 



We did not have the opportunity to make similar observations 

 on polyspermy in Chcetopterus. Such data as we have indicate 

 that there is, as in Arbacia, a comparatively narrow region in 

 which polyspermy predominates (about pH 9.5). 



