132 FERTILIZATION 



Hemicentrotus pulcherrimus. The approximate time course of the 

 capacitance change is shown in Fig. 29. The reader should beware 

 of a somewhat confusing interpretation of this phenomenon, 

 involving a large capacitance in the fertilization membrane, put 

 forward at one time by Cole & Cole (19366). This interpretation 

 is most unlikely to be correct, as Cole & Spencer pointed out 

 in 1938. The change in capacitance at fertilization is real and 

 reflects the structural changes in the cell surface which are known 



20 



1-6 



^ 1-2 

 06 



0-4 







20 



40 



60 



80 



t {mm.} after fertiLization^ 

 at t=o 



FIG. 29. — Changes in membrane capacitance of eggs of Pseudocentrotus depressus 

 following fertilization. A set of points connected by a line refers to consecu- 

 tive readings on a sub-sample containing lightly centrifuged eggs, removed 

 from one parent sample. Cleavage at 80-100 min. in parent sample. T° C, 

 i7-9-i8-5. Adapted from lida (1943a). 



to take place at that time. Apart from what might be called 

 chemical changes, the cell surface becomes thinner at fertilization, 

 because of the elevation of the vitelline (= fertilization) membrane. 

 This reduction in thickness is consistent with the observed increase 

 in capacitance, for the following reason: the capacitance of a 

 parallel plate condenser is given by the equation 



:A/477l 



(3) 



where e = dielectric constant of the medium between the plates. 



