Fig. 6. 



Simultaneous measurements of extracellular pH and cell fluorescence following fertiliza- 

 tion of S. furpuratus. Note that time is from right to left. 



The other question relates to whether the 

 observed temporal sequence might result from 

 instrumental artifacts. This is probably the 

 case in the lag between the light-scattering-pH 

 change and fluorescence change shown in Fig. 8. 

 Thus, if the observed light-scattering or acidity 

 changes were adjusted to give the same ampli- 

 tude on the chart as the fluorescence change 

 (as in Fig. 6), the temporal sequence would 

 be almost identical (within two seconds). It is 

 probable, therefore, that changes in acid ex- 

 cretion, light-scattering, and fluorescence all 



begin simultaneously, with possibly a slight lag 

 in the fluorescence change. 



The respiratory change, in all cases so 

 far examined, always begins after the above 

 changes and does not appear to result from 

 any instrumental lag. First, when fluorescence 

 and respiration rate are similarly amplified, 

 the lag is still apparent. Secondly, when an 



nnnoles 



'6 20 40 60 80 100 140 180 



Seconds After Sperm Addition 



-2 



Fluorescence Increase! 

 Light Scattering Decreasty 



— I — I — I — 1 — I — I — I — I — [ — I — I 1 

 0+1 2 3 4 5 6 



Minutes After Sperm Addition 



Fig. 7. 



Derived rates of acid excretion and cell respiration 

 following fertilization of S. purpuraius. Note that peak acid 

 excretion occurs before the increase in respiratory rate. 



Fig. 8. 



Simultaneous measurement of cell fluorescence, extra- 

 cellular pH, respiration rate and light-scattering in eggs 

 of S. purpuratus. (Data of Epel and Pressman). 



23 



