Why do the larvae of dragon-flies suck in and eject water to aid their progress in swimming?
Because the jet propels the creature through the water, in consequence of its being resisted by the stationary mass of the fluid behind it, and a contrary current being thence produced by this singular pumping. As the insect, between every stroke of the internal piston, is obliged to draw in a fresh supply of water, an interval consequently occurs between the strokes, during which it will sometimes elevate its tail above water, and squirt out a small stream like that from a little syringe. Among other purposes of this wonderful apparatus are its aid in bringing small water insects within its reach, and its share in respiration, in which it somewhat resembles the gills of fish.
