Phase-contrast light micrograph of the (wet) AP tectorium of Ascaphus truei, the tailed frog. The view is from below (the side opposite the epithelial surface of the papilla, which is on the chamber ceiling). The tectorium dangled from the chamber ceiling, the remainder of the chamber volume was filled with fluid (endolymph), as were cylidrical tubes throughout the body of the tectorium. The arrow points to a region where the fluid-filled tubes are in focus. The end of each tube was immediately adjacent to a hair bundle. The tissue was fixed (glutaraldehyde) and then placed in a buffer solution. Here it was surrounded by the buffer solution in a depression slide, covered by a thin coverslip.