The Locomotory Rhythm of the Dogfish (Scyllium Canicula)

Abstract

Recent experimental work ( v. Holst, 1935; Gray, 1936) has shown that the locomotory rhythms of certain teleostean fishes are determined by the intrinsic activity of the central nervous system, for they remain unaffected when the intervention of peripheral reflexes from the skin or muscles has been eliminated. This conclusion is at variance with that of ten Cate (1933) who removed all the muscles in the neighbourhood of the anterior dorsal fins of the dogfish (Scyllium canicula and A. catulus) and having transected the nerve cord, observed that a locomotory rhythm was propagated over the site of the operation thereby maintaining co-ordinated movement between the head and the posterior region of the body; the activity of the posterior region depends, according to ten Cate and ten Cate-Kazejewa (1933), on tensile stimuli applied to the posterior musculature whenever an active contraction occurs in the head region. If this conclusion be justified, the normal locomotory rhythm of the dogfish involves the activity of a chain of peripherally controlled reflexes whereas that of the eel is determined by a mechanism entirely independent of such reflexes. The situation appeared to be sufficiently anomalous to justify further investigation, and an attempt has been made to confirm ten Cate’s observations. The work was performed at Plymouth and Scyllium canícula was used as the most convenient material; a few observations made on 5. catulus indicated that there is no essential difference in the behaviour of the two species.