The Respiratory Movements of the Lamprey (Lampetra fluviatilis)

The branchial apparatus of Lampetra fluviatilis has been studied to find out whether the inspiratory movement is brought about by muscular contraction. Differences between existing accounts of the anatomy are pointed out, and a description is given of diagonal muscles which span re-entrant curves of the gill bars. Extirpation and stimulation experiments provide evidence that none of the available muscle groups can have an inspiratory function. The pressure changes in the gill sac indicate that the momentum of the water-stream in forceful expiration leaves a region of low pressure which initiates the inspiratory flow.