III. Preliminary observations on the locomotor system of medusæ

The movements of some of the Medusae (e. g. Sarsia) appear to be as voluntary as are those of insects. Some of the discophorous species of naked-eyed Medusae*, when threatened with injury, manifest peculiar movements, which are quite distinct from the ordinary locomotor contractions. These movements consist in a very strong and protracted systole, followed by a slow and gradual diastole. This spasm-like series of movements is never performed by any Medusa except when the animal is being injured or threatened with injury.