Bell-Divers of the Two-Doored Diving-Bell — an age when a lagoon-city's pearl-guild lowers a single great bronze diving-bell whose one hatch does not open the chamber onto the water below but folds the passage back through its own rim: the same round bronze mouth a Diver is plunging DOWN through toward the black pearl-beds she can see glinting beneath her is, in the same casting in the same instant, already delivering her UP through the same rim back into the air-filled bell she just left above her, so the deep water below is the breathing chamber above, and the hatch has no waterline and no lip, only the seam where dive is surface — and the Bell-Divers have learned the hatch cannot be swum through, only crossed at the fold in one committed pushing stroke off the bronze rim, one bare foot driving her toward the pearl-beds while that same push carries her back up into the bell's caught breath behind her, hung mid-dive between the drowned dark and the dry air of the same bronze mouth before the two-doored bell decides which surface the tide will let her break