Confocal laser-scanning microscopic image of the cells in the threadlike structure stained with acridine orange. (a) Typical longitudinal image of the whole threadlike structure. Note that the cells (arrowheads in bottom inset) in the vessel are linearly aligned along the longitudinal axis of the vessel. (b) Acridine orange-stained cells in the node (marked as “b” in (a)) showing the small round cells with green nuclei (arrowheads) and large cells with green nuclei and red granules (arrows). (c) Acridine orange-stained cells in the vessel (marked as “c” in (a)). Note that the density and alignment of resident cells are different in the node (b) and in the vessel (c).