Studies On the Myoneural Physiology of Echinodermata

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Abstract
1. The lantern retractor muscle of Parechinus angulosus responds to light stimulation by a rapid contraction which is followed by a slower increase in tension. The details of these contractions vary from preparation to preparation. 2. With very brief light exposures only the quick response is shown, while with prolonged light stimulation rhythmical activity develops after a minute or more. 3. Exposure of a contracting preparation to the light of a mercury vapour lamp causes a slight fall in tone. This is not due to the ultra-violet component of this light. 4. Responses to repeated light pulses may result in simple summation or the response to the first pulse may be markedly greater than those which follow. In preparations which show this latter effect, there is evidence for an inhibitory phenomenon which persists for about 30 sec. 5. With paired stimuli the response to the second stimulus may show an initial depression which reaches a maximum at an interval of about 10 sec., then a recovery and finally a second depression of response which is maximal when the interval between stimuli is about 5 min. 6. There is evidence that stimulation of the comminator muscles may result in loss of tone of the lantern retractor muscles. 7. A provisional hypothesis to explain these effects is presented.

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