« AnteriorContinuar »
One anomalous form, standing, as it were, between the sharks and rays,—the monk, or angel-fish (Rhina squatina),—affords in its locomotive characters an interesting link further indicating its close affinity rather with the former than with the latter group. The habits of this fish are essentially nocturnal, and throughout the daytime it usually reclines sluggishly at the bottom of its tank. Its depressed body and broadly expanded pectoral fins resemble those of a ray more than a shark, and like the former fish it seeks concealment by burying itself beneath the sand or shingle, excavating a hole with the shovel-like action of these broad fins, and thus waits in ambush for passing prey. Immediately the monk-fish rises above the surface of the ground its true affinities become apparent, progression being effected entirely by the lateral action of the caudal extremity, as in the sharks, though in a more slow and clumsy manner. The lateral position of the gill-openings in this fish forms its chief shark-like anatomical character, and to this has to be added its viviparous habits.
In the Batoidea, or ray tribe, onward motion is accomplished by a singular, even, and wing-like action of the broad pectoral fins, the attenuated caudal extremity remaining perfectly quiescent, and serving only to preserve the fishes' equilibrium. Swimming towards the surface of the water, these fish present a most remarkable birdlike aspect, their large flapping fins reminding the observer of the flight of the heron or some other unwieldy representative of the Grallian order, while the slender tail dependent in the rear suggests the characteristic mode in which those birds hold their long legs, while pursuing their course through the more subtle medium which they inhabit.
Proceeding to the Teleostean group, we find the means by which the same organs are made subservient to the faculty of locomotion, still more highly diversified; space, however, will only admit of a few selections.
In the gurnards (Trigla), during rapid movement, all the fins are pressed closely against the body, the broad wing-like pectorals being shut up like a fan, while the fish is propelled swiftly through the water by the vigorous undulations of the tail; when the fish moves leisurely the pectorals are opened to their full extent, acting as balances. In many species, such as the striated gurnard (T. lineata), these fins are brilliantly coloured, reminding the observer, especially when regarding them from above, of gorgeous tropical butterflies, gliding along with the smooth action characteristic of the Vanessa tribe. Yet a third property of motion is possessed by these remarkable fish. Settling on the ground at the bottom of the water, they are capable of literally walking over it by means of the three free rays of the pectoral fins, which are situated a little in advance of the others, and are curved and especially thickened, to adapt them for their anomalous office.
The gemmeous dragonet (Callionymus lyra), a small and beautiful fish somewhat resembling the gurnards in outward appearance, is distinguished by an essentially different mode of progression. The habits of this species are rather sluggish; it spends much time reclining on the ground, occasionally moving for short distances just above its surface, by the flitting action of the delicate pectoral fins. On ascending towards the top of the water, its swimming capacities are shown to be very limited, being restricted to the weak vibrations of the pair of fins above mentioned, and which impart to it a peculiar jerky action. The male in this species is recognized by the extraordinary length of the first ray of the anterior dorsal fin, which is raised and depressed at pleasure like the latteen sail of a Mediterranean fishing-yawl. This singular appendage appears, from my own observations of the species in confinement, to be subservient to the same end as the wattles, crests, and other abnormal adjuncts of the male in the Gallinaceous birds—for the purpose of fascinating their mates; to this is added a similar heightening of the colour, which is carried to such an extent in this fish that the two sexes were long regarded and described as separate species, under the respective titles of Callionymus lyra and dracunculus.
In the pipe-fish and sea-horses (Syngnathm and Hippocampus), representatives of the Lophobranchii, the organs of locomotion are reduced to their minimum, being often restricted, in the former genus, to a single median dorsal fin, and being at the most supplemented by a pair of diminutive pectorals and a rudimentary caudal. In all cases this dorsal fin is the chief propelling instrument, and in motion, rapidly undulating from end to end, illustrates the action of the Archimedian screw, driving the fish through the water on the same principle. Dr. J. E. Gray was the first to point out this remarkable peculiarity, in the case of Syngnathus, from observing these fish in the aquarium at the Zoological Gardens. In both Syngnathus and Hippocampus the animal usually assumes a vertical position while progressing through the water.
The John Doree (Zeus faber) affords us an example of the same principle noticed in the Syngnathidae, applied to the purposes of locomotion, though in a still more remarkable and extensive degree. One of these singular-looking fish added to the Brighton tanks about two months since has continued in perfect health up to the present time; and, although of shy and retiring habits, has already yielded many points of interest in connection with its life-history. The ordinary position assumed by this fish is the neighbourhood of some projecting rock near the bottom of its tank, and against which it sometimes inclines in a leaning posture, remaining motionless for hours together. Its ordinary progress from place to place is remarkably slow, and it is only when on rare occasions it rises high in the water that the beautiful mechanism that guides its movements can be appreciated. It may then be seen that the only organs called into action are the narrow and delicate membranes of the posterior dorsal and anal fins, each of which vibrates in a similar manner to the single dorsal of the pipe-fish; the long filamentous first dorsal, pectorals, ventrals, and caudal fins meanwhile remaining perfectly motionless. Thus this wary fish, with an almost imperceptible action, silently and stealthily advances upon its intended prey, engulphing it in its cavernous mouth almost before the hapless victim is aware of its enemy's approach.
W. Saville Kent.
Tlie Denizens of Aquariums.* By Edward Newman.
Seals.—I am induced by Mr. Kent's able paper to make public a few observations of my own, not very new or very recently made; and I will begin with seals, lung-breathing animals, which I fear we shall never see at the Crystal Palace, on account of Mr. Lloyd's conscientious objection to their introduction,—an objection which happily is not felt at Brighton, so that the visitors of that establishment are there allowed the opportunity of observing the peculiar actions of these most interesting animals. My first acquaintance
* Having eschewed the language of Science for so long a period, I cannot adopt it now: our friend Mr. Lloyd uses it in a preceding paper, doubtless fearful that his continental friends might fail to understand our English plural aquariums, hut I cannot persuade myself to follow him.
with seals was made at Roundstone, in Connemara, in July, 1839, where I had abundant opportunity of seeing then) at home: the date seems to take me back into the dim ages of remote antiquity, but memory still reproduces with the utmost clearness the facts then observed. Nothing can be more smooth and comfortable than the manner in which a seal slides or glides or launches himself into the water; it seems the result of gravitation only, and often independent of muscular exertion; but when he leaves the water these conditions are exactly reversed; then his efforts are most laborious, and he reminds us of a man jumping in a sack; his progress consists of a series of spasmodic and ineffectual jerks, which he fondly mistakes for leaps: he verifies most minutely Virgil's celebrated apothegm:—
"Facilis descensus pelagi. • • • • •
Sed revocaro grftdum superasque evadere ad auras
Hoc opus, hie labor est."
How often have our moralists applied this passage to poor man's facilities for transgression and the difficulty of his return to rectitude; but with the alteration of a single word, the seal gives us a far more apt illustration of the poet's meaning. Revenons a nos moutons; I must put Virgil on the shelf and return to my denizens. The moment a seal has fairly launched himself in the water, he turns over on his back, and swims in this reversed position: incredible as it may appear, he will be quite willing at any time of the day to verify this at Brighton, and will convince the most sceptical of the truth of my assertion. Why is this? wherefore should a seal swim on his back with his stomach uppermost? Let us speculate a moment. If we attentively study the position of his eyes, we shall see that they are placed so as to look upwards with the greatest ease, and thus apprise him of all dangers when on land or on ice. Such enemies as man and the white bear, both of whom are ever on the look out for him, are thus readily perceived, and often by a timely movement avoided. When in the sea it is different; his object then is to feed; men and bears do not pursue him so incessantly or so availingly in the deep; but his food swims beneath him, and to be eaten must be caught, and to be caught must be seen. The seal has no means of dredging the sea; he must see and pursue each individual fish on which he desires to feed. The eyes of a seal are placed in the best possible position for perceiving men and bears when on land and ice and
SECOND SERIES—VOL. IX. L
fishes in the sea: were it reversed he would not long maintain his amphibious existence.
Well then, as to the action of swimming, how is this performed? partially by his paddles and partially also by the movements of his spinal column. I am told,—and I believe it notwithstanding the danger of accepting any "I am told" in Natural History,— that whales and porpoises invariably move the vertebral column vertically—that is, upwards and downwards; now it is well known that fishes move the spinal column from side to side or horizontally; this may be seen every day in an aquarium. Seals adopt the plan of fishes, and swing their vertebral column aud posterior extremities from side to side. I never cease to regret having missed the opportunity of seeing the porpoises at Brighton: it may not occur again: then indeed I might have witnessed and verified that vertical action which now I am obliged to take for granted. It must be admitted that the structure of a porpoise entirely favours this conclusion, but how often are conclusions from structure erroneous, because we mistake the meaning of the structure.
Turtle.—The action of a turtle in the water is very beautiful; his anterior paddles move slowly, sedately, and simultaneously, like the wings of a rook returning at eventide from its wearisome and monotonous labour of delving in the earth for wireworms: faithful slave of man, it receives a slave's reward.
Mackerel.—A word on mackerel: our friends at Brighton have succeeded in keeping mackerel alive for weeks—a great triumph, but, alas! the result is disappointing: the mackerel is of all fishes the least graceful, the least easy in its movements: possessing a form the very model of symmetry, it nevertheless swims with difficulty and apparent timidity, just as a human being afflicted with lumbago is reluctant to move a muscle from a dread of the consequences.
The Sleep of Fishes.—How often has the enquiry been made, Do fishes sleep? and how futile and unsatisfactory have been the answers; I suppose scarcely any one recollects a clear and decided solution. The question may be extended and enlarged, and fishes, with regard to the act of taking rest in sleep, may be divided into diurnal aud nocturnal, a division which I may state, with some degree of confidence, has never been worked out. Before you can answer the simple question, Do fishes sleep? you must of necessity inform yourself of the habits of the fish you would place in the