Fig. 13.20. Electron micrographs of sea iirchiu spermatozoa (llonicentrotus pulclicrriniu.s) : 

 A, control, formalin-fixed in sea water; B, formalin-fixed two seconds after addition of egg 

 water showing breakdown in acrosomal region and extrusion of protoplasmic mass; C, for- 

 malin-fixed 20 seconds after addition of egg water; D, formalin-fixed three minutes after 

 addition of egg water. The agglutination which results from the addition of egg water is re- 

 versed at 2.5 minutes. (Photographs courtesy of J. C. Dan.) 



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