. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 824 Comparative Animal Physiology complete deafferentation but the rhythm can be transmitted across a deaf- ferented region of the cord. About 25 continuous intact segments in any part of the cord are needed to maintain the rhythm. Swimming in elasmo- branchs apparently depends on reflex excitation, and peripheral connections are essential, but the cord is capable of transmitting the rhythm through a region where the nerve roots have been cut. Stimuli which accelerate the swimming rhythm in normal fish inhibit i
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. 824 Comparative Animal Physiology complete deafferentation but the rhythm can be transmitted across a deaf- ferented region of the cord. About 25 continuous intact segments in any part of the cord are needed to maintain the rhythm. Swimming in elasmo- branchs apparently depends on reflex excitation, and peripheral connections are essential, but the cord is capable of transmitting the rhythm through a region where the nerve roots have been cut. Stimuli which accelerate the swimming rhythm in normal fish inhibit it in spinal or fatigued fish. Spinal dogfish show a variety of reflexes, particularly of fins; a single segment iso- lated from the rest of the cord can mediate homolateral and crossed re- sponses.^^®- ^^^ Spinal teleosts also show fin reflexes elicited from localized sensory areas,"*^* some of them enhanced, that is, released from cephalic inhibition by the spinal section.^^^ There appears to be much difference in autonomy of the cord from genus to genus. In fish which swim by undulatory waves, as the. Fig. 308. Rhythmic responses of posterior abdomen of goldfish (Carassius) to stream of water appHed at side of body, after transection of cord, a, at about vertebra 16; h, at vertebra 7; c, between vertebra 7 and medulla; d and e, at anterior meduUa, ahead of vagus root. From Holst.^ eel, section of the cord interferes very little with swimming. An eel still swims when the skin is removed and when the muscles of a quarter of the body are removed. It is as if the undulatory rhythm were inherent in the cord and normally released by the medulla or by peripheral stimulation.^'^•^ Fish which swim with fins show little or no swimming when the cord is tran- sected ;^' ~^^ Simple reflex responses of the fins and tail region are easily elicited and the sensitivity of- the skin to a stream of water may actually be enhanced after spinal section, as demonstrated in
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