Damselfly larva gill. Darkfield illuminated light micrograph of part of the caudal gill of a damselfly (suborder Zygoptera) larvae, showing the tracheoles (tubes, lines) of the respiratory system. Damselfly nymphs are aquatic and breathe using three caudal gills located at the tail end of the abdomen. The gills are laced with fine branching vessels that carry oxygen absorbed from the water to the tissues. Magnification: x400, when printed 10 centimetres wide.