Page:Proceedings of the Royal Society of London Vol 1.djvu/231

Rh ably large; but the muscles have no tendinous chords, their insertions being always ﬂeshy. There are, however, semi-transparent pearly tendons placed between the plates of muscles, which give origin to a series of short muscular ﬁbres, passing nearly at right angles between the surfaces of the adjoining plates.

The progressive motion of ﬁshes, our, author says, is chieﬂy performed by the ﬂexions of the trunk and tail; the pairs of ﬁns, which some have considered as analogous to feet, being only employed for the purposes of turning, stopping, altering the position of the ﬁsh towards the horizon, and keeping the hack upwards. The single ﬁns appear to prevent the rolling of the body whilst the tail is employed to impel it forwards. Each of the ﬁns, which are in pairs, is capable of four motions, viz. of ﬂexion and extension, like oars, and of expanding the rays, and closing them.

Mr. Carlisle now (taking the Cod as a standard of comparison,) describes particularly the mode in which the various motions here spoken of are performed, and then relates some experiments made to determine the effect of the ﬁns on the motions of ﬁshes. For this purpose a number of dace, equal in size, were put into a large vessel of water, and the pectoral ﬁns of one of them being out off, it was replaced with the others. The result was, that the progressive motion of the ﬁsh was not at all impeded; but its head inclined downwards; and when it attempted to ascend, the effort was attended with difficulty.

From another ﬁsh, both the pectoral and abdominal ﬁns were taken. The ﬁsh remained at the bottom of the vessel, and could not be made to ascend. Its progressive motion was not perceptibly more slow; but when the tail acted, the body showed a tendency to roll, and the single ﬁns were widely expanded, as if to counteract this effect.

From a third ﬁsh the single ﬁns were removed. This produced an evident tendency to turn round, and the pectoral ﬁns were kept constantly extended, to obviate that motion.

From a fourth ﬁsh all the ﬁns were removed. Its back was kept in a vertical position, whilst at rest, by the expansion of the tail; but it rolled half round at every attempt to move.

From a ﬁfth ﬁsh the tail was cut off as close to the body as possible. The progressive motion of the ﬁsh was considerably impeded, and the ﬂexions of the spine were much increased; but neither the pectoral nor the abdominal ﬁns seemed to be more actively employed.

From a sixth ﬁsh all the ﬁns and the tail were removed. It remained without motion, ﬂoating near the surface of the water, with its belly upward.

The above experiments were repeated on the roach, the gudgeon, and the minnow, with similar results.

Mr. Carlisle now observes, that the muscles of ﬁshes differ very materially in their structure from those of other animals; that they are apparently more homogeneous; that their ﬁbres are not so much fasciculated, but run more parallel to each other, and are always