title: External calcium ions are requisite for fertilization of sea urchin eggs by spermatozoa with reacted acrosomes.
mesh_terms: D000177:Acrosome / Q000502:physiology* / Q000648:ultrastructure; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D005306:Fertilization / Q000187:drug effects*; D008297:Male; D012617:Sea Urchins / Q000187:drug effects / Q000502:physiology*; D013094:Spermatozoa / Q000502:physiology*
chemical_list: D002118:Calcium