340 



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



pH 7.1; the latter is perfectly and instantly reversible, as in As- 

 terias and Arbacia, disappearing as soon as the eggs are returned 

 to a more alkaline solution. 



THE INFLUENCE OF ALKALI ON THE FERTILIZATION REACTION. 

 Frank Lillie (5) has observed that the addition of alkali to the 

 sea water in which insemination occurs increases the incidence of 

 fertilization in Asterias and Arbacia eggs of poor quality. We 

 have confirmed this in Asterias and Arbacia and found that it is 

 equally true for Cli&topterus. This effect of a slight increase in 

 alkalinity in aiding fertilization may be due to action on the sperm 

 but it seems more probable that both the eggs and the sperm are 

 affected. The changes which culminate in increased fluidity of 

 the egg cortex in alkaline sea water (3) are no doubt preceded by 

 enhanced physiological reactivity. 



Apart from this stimulating action of alkali, which is not appar- 

 ent in eggs of the best quality, fertilization in Asterias and Arbacia 

 proceeds unimpaired from pH 8.15 to 9.6. With further in- 

 creases in alkalinity, eggs appear in increasing numbers which 

 have either tight or incompletely formed fertilization membranes ; 

 and at pH 10.2 the eggs have no demonstrable membranes at all. 

 When returned to sea water after a 3 to 5 minute exposure to pH 

 10.0, fertilization membranes will form on most of the previously 

 unmembraned eggs. It was concluded that these eggs were ferti- 

 lized while in the alkaline solution, since 'the supernatant sperm 

 carried over from the alkaline solution are incapable of fertilizing 

 fresh eggs. Longer exposures injure the eggs to such an extent 

 that membranes do not form on them when they are returned to 

 sea water. The H-ion concentrations which prevent membrane 

 elevation (and which destabilize the cortex of the unfertilized egg 

 (4) ) are shown in Figs. I and 2 by the dotted lines at the extreme 

 right. 



This alkaline injury is more rapid in Asterias than in Arbacia. 

 In the latter case the eggs will divide imperfectly if returned to sea 

 water after a 5 to 10 minute exposure to the alkaline solution. In 

 Asterias the inhibition of membrane elevation is rapidly followed 

 by a more profound injury which completely stops development. 

 Such eggs can not be fertilized by fresh sperm in sea water. 



These facts all indicate that under increased alkalinity union 

 of the egg and sperm still occurs; but if the increased alkalinity 



