title: Fine structural investigation of the insemination response in Urechis caupo.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D005260:Female; D005306:Fertilization; D007448:Invertebrates / Q000648:ultrastructure*; D008297:Male; D010063:Ovum / Q000378:metabolism / Q000648:ultrastructure*; D013084:Sperm-Ovum Interactions; D013499:Surface Properties; D013997:Time Factors