title: An old enigma: the gray crescent of amphibian eggs.
mesh_terms: D000663:Amphibians / Q000196:embryology*; D000818:Animals; D001001:Anura; D002455:Cell Division; D002462:Cell Membrane / Q000648:ultrastructure; D002463:Cell Membrane Permeability; D003599:Cytoskeleton / Q000648:ultrastructure; D004530:Egg Yolk; D005260:Female; D005306:Fertilization; D007839:Functional Laterality; D006112:Gravitation; D008854:Microscopy, Electron; D009024:Morphogenesis / Q000528:radiation effects; D009865:Oocytes / Q000648:ultrastructure; D010063:Ovum / Q000166:cytology* / Q000528:radiation effects / Q000648:ultrastructure; D010312:Parthenogenesis; D011894:Rana pipiens / Q000196:embryology; D014319:Triturus / Q000196:embryology; D014466:Ultraviolet Rays; D014981:Xenopus / Q000196:embryology