Copulatory activity is described in Enallagma cyathigerum; some observations on reproductive behaviour of Calopteryx splendens and some other zygopterans are also included. Copulatory activity is divisible into 3 stages: in stage /, which may occupy more than 75% of the time, there are continual rhythmical movements of the abdomen of the male. In stage II, the abdominal positions change and a new type of rhythmic activity appears, also due to the male, while in stage III, the positions again change but there are no visible movements. Dissection of pairs killed at different stages of copulation suggests that stage I may be concerned with sperm removal from the female, while during //and ///sperm is transferred to the female. The female cannot escape from the tandem association but can accept or reject copulation, and she may terminate the activity during stage /. Stages //and III have not been seen to be spontaneously interrupted. — Dissection of the male secondary genitalia and their examination in scanning electronmicrographs shows the penis head to possess a variety of hooks and bristles. These have been seen to hold trapped sperm when pulled from females in copula. In restrained decapitated males, activity of the penis and associated movements of abdominal segments occur spontaneously or can be evoked mechanically. They resemble the activity occurring naturally in stage /, Electromyograms have been used to verify the contributions of 3 sets of muscles to the movements.