1. The activity of the buccal ganglion of Aplysia depilans is manifested as regular and sequential bursts of nerve impulses.

2. Regularly firing bursts are seen in the absence of feeding movements.

3. Sequences of bursts lasting for several minutes have been recorded during feeding movements induced by a natural stimulus.

4. A feed-back system has been used to produce bursts in certain other cells synchronous with the regularly firing units.

5. During sequences of bursts there is an alternation of activity between the two groups of neurones.

6. One group is made up of four cells discharging synchronously but within different ranges of frequency.

7. A mathematical model of this activity will be presented in another paper.

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