Aeshnid larvae respire through tracheal gills. These are located in a modified region of the hind gut, the branchial chamber, and are ventilated by muscular movements which effect a flow of water into and out of the anus. Normal ventilation is a rhythmic process, with expiration occurring first. The nature and nervous control of this and other forms of ventilation, including jet-propulsive swimming, ate analysed in terms of morphology, mechanics and neurophysiology. It has been known for some time that anisopteran dragonfly larvae respire through tracheal gills located in a modified posterior region of the alimentary canal known as the branchial chamber (AMANS, 1881; MATULA, 1911; TIL-LyARD, 1917; WALLENGREN, 1913, 1914 a, 1914 b). However, TONNER I was the first to describe different types of ventilatory movements. He istmguished normal, gulping and chewing ventilation, and in addition noted at the jet-propulsive mechanism of swimming, in which the larva ejects a current of water from its anus, would also subserve respiration. The various types of have been further analysed in recent years by HUGHES & MILL (1966), MILL (1970), MILL & HUGHES (1966), MILL & PICKARD (1972) and HJCKARD& MILL (1972).