Summary
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1.
The paradoxical behaviour of the sphincter ofCalliactis parasitica in intact animals (Fig. 2) and preparations during low-frequency electrical stimulation has been examined.
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2.
The apparent differences in behaviour can be attributed to aging effects (Fig. 4) occurring within the preparation. This is due to the endodermal circular muscles (Fig. 5) which line the sphincter and become increasingly excitable as the preparation ages.
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3.
A unique inhibitory response acting on the sphincter muscle has been revealed. It acts to delay the onset of slow contraction until after the low-frequency electrical stimulation has ceased.
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4.
A study of spontaneous activity in unstimulated preparations has revealed the means by which activity in different conduction systems can influence activity of the sphincter and column circulars (Fig. 6). Evidence is presented to suggest that the inhibitory response plays an active role in these functions.
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5.
It is proposed that the inhibitory response plays an important role in basic behavioural activity, such as slow closure sequences.
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I am grateful to Dr. I.D. McFarlane for his helpful suggestions and advice throughout the course of this work, and to Prof. D.M. Ross for reading the manuscript of this paper. This work was supported by a Science Research Council Research Studentship grant.
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Lawn, I.D. The marginal sphincter of the sea anemoneCalliactis parasitica . J. Comp. Physiol. 105, 287–300 (1976). https://doi.org/10.1007/BF01379289
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DOI: https://doi.org/10.1007/BF01379289