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.
The nerve cord being transected at the level of the fifth or sixth vertebra.
The diagrams shown in Figs. 1-3 have been prepared by an analysis of photographic records. The vertical lines ab, a1bi represent the approximate antero-posterior axis of movement. The frequency and duration of each beat can be judged by the time scale on the left of the diagrams and the amplitude by the total excursion from left to right. The records read from top to bottom. The positions of the tail as shown by individual points on the curves have not, in these figures, been recorded for the same instants of time as those defining the position of the head. Records of the latter type exhibit equally well the essential characteristics of the movement.
The behaviour of these fish is strikingly similar to those described by ten Cate, but the two sets of experiments are not comparable since the spinal cord in our experiments was intact.
A spinal preparation of the conger (Conger vulgaris) appears to exhibit rhythmical activity much more readily than that of the fresh-water eel. During the first few weeks after spinal transection behind the medulla, a single specimen readily exhibited prolonged rhythmical activity in the hinder end of the body after gentle stimulation; three months after the operation the rhythm became persistent, von Holst (1934) has reported spontaneous spinal activity in some specimens of Anguilla vulgaris.
