8/15/2023 0 Comments Dragonfly larvae illustrationThe branchial chamber pressure and electrical activity of the respiratory dorso-ventral muscles were measured simultaneously in an animal glued to a polyethylene stick by its wing buds. Since there is no labial muscle that is large and powerful enough to produce the rapid movement, a hydraulic system was postulated to be the direct source of the power required for this movement because of the following indirect evidence : a quick contraction goes through the body when the labium is suddenly protruded ( Munscheid, 1933) the anal valve is found to be closed at the moment when the bulge appears in the labial joint ( Pritchard, 1965) in an anaesthetized specimen, compression of the abdomen and thorax results in a lifelike forward swing of the labium ( Snodgrass, 1954) the rapid increase in blood pressure, which occurs when the anterior dorso-ventral muscles of the abdomen contract, is invariably followed by labial extension ( Olesen, 1972). The mechanism of the movement and the mus-culature of the labium have been studied ( Amans, 1881 Whedon, 1927 Munscheid 1933 Snodgrass, 1954), but the function of the individual muscles in the movement or the labium has not been explained conclusively. In Aeschna eremita full extension of the labium takes only 16–25 ms ( Pritchard, 1965). Once the click is disengaged the internal pressure produces the large torque to move the labium with great acceleration during the mid phase.ĭragonfly larvae are aggressive predators, which catch their prey by protruding heir labia with great rapidity. The stored energy in the extensor system is released suddenly and disengages the click producing the initial phase. The strike movement begins when the flexor muscles relax. The extensor muscles and the primary flexor muscles co-contract for 75–100 ms before the strike. The geometry of the labial joints gives the primary flexor muscles of the labium a large mechanical advantage over the extensor muscles in the fully flexed labium, and allows the extensor muscles to contract almost isometrically. The required pressure for the mid phase is about 60 cm H 2O if the resistance is neglected and 80 cm H 2O when the resistance is considered.Ībdominal dorso-ventral muscles contract 110–500 ms before the onset of the strike and the body pressure of the animal increases to a peak of 40–120 cm H 2O at the onset of the strike. The power for the mid phase is derived from the internal body pressure developed by the contraction of the abdominal dorso-ventral muscles. The power production of the extensor muscles is less than the power output of the mid phase. No torque develops about the postmentum-prementum joint as long as the click of the flexed labium is engaged. The relation between the pressure applied to the labium and the extension torque at the joints has been established. The torque necessary for the acceleration was calculated to be 1♳ × 10 −5 and 4♰ × 10 −5 N.m for the initial and mid-phases respectively. s −2 during the initial and mid phase respectively. The angular acceleration of the joints of the labium is 2♶ × 10 5 and 7♸ × 105 deg. The strike movement consists of an initial, mid and late phase. The mechanism of this movement was analysed by high-speed cinematographs and by hydrostatic and electrophysiological measurements. Aeschna larvae catch prey with a fast-moving elongated labium.
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