The Immobilization of Locomotory Movements in the Earthworm, Lumbricus Terrestris

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Abstract
1. In response to stimuli at the head, a peristaltic wave travelling in any part of the earthworm's body may be arrested. This occurs after an interval of about 0.5 sec., if the nearest part of the wave is 5 cm. from the point of stimulus. This response is of regular occurrence, and it depends on the continuity of the nerve cord between the point of stimulus and the region of the wave. It is therefore named the reflex arrest of peristalsis. 2. The arrest of peristalsis is brought about by the complete cessation of movement of both the elongation phase and the shortening phase of the wave. The shape of the wave is not lost; though it appears that there may be some relaxation of the circular muscles in the region of elongation. 3. The receptors of the reflex lie on the cephalic half of the body. Stimuli applied on the most cephalic one-third of the body may arrest a peristaltic wave cephalic to their point of application. 4. The response may appear in answer to mechanical or to chemical stimuli. It may also appear in response to the absence of contact with the substratum in the head region. In this last case the reflex depends upon the presence of the supraoesophageal ganglion. The response to mechanical stimuli, however, depends neither on the presence of the cephalic one-third of the body, nor on the presence of the tail segments. 5. A similar reflex arrest of anti-peristalsis occurs in response to mechanical or chemical stimuli on the caudal half of the body. The time interval between stimulus and response at 5 cm. from the point of stimulus is about 0.4 sec. The anti-peristaltic wave was not observed to be arrested while travelling in the most cephalic one-third of the body. 6. The arrest of the anti-peristaltic wave is due, too, to a cessation of movement of both phases of the wave, without a loss of its general shape. 7. The receptors for the reflex lie in the caudal half of the body, and the nerve paths from them run in both directions. The reflex does not depend on the presence of either the head or the tail segments. It can be obtained in a worm with the most caudal one-third of the body removed, or in a worm with the most cephalic one-third cut off. 8. The arrest of an anti-peristaltic wave by the development of a peristaltic wave can be observed in the spontaneous reversal of the direction of crawling. This act of behaviour, which is named the spontaneous immobilization of anti-peristalsis, does not depend on the presence of either the most cephalic one-third or the most caudal one-third of the body. Though this act of behaviour need not be considered as a reflex, its performance depends on the continuity of the nerve cord between the new peristaltic wave and the anti-peristaltic wave that is immobilized. 9. The above three acts of behaviour are distinct from each other in their paths in the cord, and the two reflexes are distinct in their receptors. All three play an important part in one or more larger patterns of behaviour. All are conducted in paths separate from those conducting the rapid shortening reflexes. 10. There is little evidence to throw light on the mode of action of these three immobilizations. They may be compared to the "freezing" of movement into posture found in insects and vertebrates. It is to be expected that their mechanism will prove to lie within the central nervous system.

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