The control of hindgut motility in the lobster,Homarus gamma rus(L.)

Two types of motor activity pass from the sixth abdominal ganglion (6 A.G.) via the posterior intestinal nerves (P.I.N.’s) to the hindgut of Homarus. These have been designated unitary or non‐repetitive and bursting or repetitive activity. They are not entirely exclusive of one another. 2. The unitary discharge is produced by at least one and possibly two interneurones (I1) whilst another class of interneurone (I2) produces bursting output. 3. Both forms of motor output are paired between branches of the P.I.N.’s. This pairing may be due to either anatomical or physiological methods of connectivity. 4. The bursting discharge is completely immutable and is not affected by extirpation of sensory input. We have attempted to explain this immutability on the basis of a fixed neuronal network in the 6 A.G. involving precise connectivity patterns. 5. Non‐repetitive units produce faily weak hindgut peristalsis whilst the bursting discharge produces very powerful contractions. We suggest that burster neurones innervate both circular and longitudinal muscles whilst exclusively unitary neurones only innervate the longitudinal musculature. The role of neurones which can assume both types of discharge is not clear.