Animal Locomotion; or, walking, swimming, and flying / With a dissertation on aëronautics

by James Bell Pettigrew

Fig. 37.—The Sea-Bear (Otaria jubata), adapted principally for swimming and diving. It also walks with tolerable facility. Its extremities are larger than those of the seal, and its movements, both in and out of the water, more varied.—Original.

This remarkable creature, which I have repeatedly watched at the Zoological Gardens[48] (London), appears to fly in the water, the universal joints by which the arms are attached to the shoulders enabling it, by partially rotating and twisting them, to present the palms or flat of the hands to the water the one instant, and the edge or narrow parts the next. In swimming, the anterior or thick margins of the flippers are directed downwards, and similar remarks are to be made of the anterior extremities of the walrus, great auk, and turtle.[49]

The flippers are advanced alternately; and the twisting, screw-like movement which they exhibit in action, and which I have carefully noted on several occasions, bears considerable resemblance to the motions witnessed in the pectoral fins of fishes. It may be remarked that the twisting or spiral movements of the anterior extremities are calculated to utilize the water to the utmost—the gradual but rapid operation of the helix enabling the animal to lay hold of the water and disentangle itself with astonishing facility, and with the minimum expenditure of power. In fact, the insinuating motion of the screw is the only one which can contend successfully with the liquid element; and it appears to me that this remark holds even more true of the air. It also applies within certain limits, as has been explained, to the land. The otaria or sea-bear swims, or rather flies, under the water with remarkable address and with apparently equal ease in an upward, downward, and horizontal direction, by muscular efforts alone—an observation which may likewise be made regarding a great number of fishes, since the swimming-bladder or float is in many entirely absent.[50] Compare with figs. [33], 34, 35, and [36], pp. 73 and 74. The walrus, a living specimen of which I had an opportunity of frequently examining, is nearly allied to the seal and sea-bear, but differs from both as regards its manner of swimming. The natation of this rare and singularly interesting animal, as I have taken great pains to satisfy myself, is effected by a mixed movement—the anterior and posterior extremities participating in nearly an equal degree. The anterior extremities or flippers of the walrus, morphologically resemble those of the seal, but physiologically those of the sea-bear; while the posterior extremities possess many of the peculiarities of the hind legs of the sea-bear, but display the movements peculiar to those of the seal. In other words, the anterior extremities or flippers of the walrus are moved alternately, and reciprocate, as in the sea-bear; whereas the posterior extremities are lashed from side to side by a twisting, curvilinear motion, precisely as in the seal. The walrus may therefore, as far as the physiology of its extremities is concerned, very properly be regarded as holding an intermediate position between the seals on the one hand, and the sea-bears or sea-lions on the other.

Swimming of Man.—The swimming of man is artificial in its nature, and consequently does not, strictly speaking, fall within the scope of the present work. I refer to it principally with a view to showing that it resembles in its general features the swimming of animals.

The human body is lighter than the water, a fact of considerable practical importance, as showing that each has in himself that which will prevent his being drowned, if he will only breathe naturally, and desist from struggling.

The catastrophe of drowning is usually referrible to nervous agitation, and to spasmodic and ill-directed efforts in the extremities. All swimmers have a vivid recollection of the great difficulty experienced in keeping themselves afloat, when they first resorted to aquatic exercises and amusements. In especial they remember the short, vigorous, but flurried, misdirected, and consequently futile strokes which, instead of enabling them to skim the surface, conducted them inevitably to the bottom. Indelibly impressed too are the ineffectual attempts at respiration, the gasping and puffing and the swallowing of water, inadvertently gulped instead of air.

In order to swim well, the operator must be perfectly calm. He must, moreover, know how to apply his extremities to the water with a view to propulsion. As already stated, the body will float if left to itself; the support obtained is, however, greatly increased by projecting it along the surface of the water. This, as all swimmers are aware, may be proved by experiment. It is the same principle which prevents a thin flat stone from sinking when projected with force against the surface of water. A precisely similar result is obtained if the body be placed slantingly in a strong current, and the hands made to grasp a stone or branch. In this case the body is raised to the surface of the stream by the action of the running water, the body remaining motionless. The quantity of water which, under the circumstances, impinges against the body in a given time is much greater than if the body was simply immersed in still water. To increase the area of support, either the supporting medium or the body supported must move. The body is supported in water very much as the kite is supported in air. In both cases the body and the kite are made to strike the water and the air at a slight upward angle. When the extremities are made to move in a horizontal or slightly downward direction, they at once propel and support the body. When, however, they are made to act in an upward direction, as in diving, they submerge the body. This shows that the movements of the swimming surfaces may, according to their direction, either augment or destroy buoyancy. The swimming surfaces enable the seal, sea-bear, otter, ornithorhynchus, bird, etc., to disappear from and regain the surface of the water. Similar remarks may be made of the whale, dugong, manatee, and fish.

Man, in order to swim, must learn the art of swimming. He must serve a longer or shorter apprenticeship to a new form of locomotion, and acquire a new order of movements. It is otherwise with the majority of animals. Almost all quadrupeds can swim the first time they are immersed, as may readily be ascertained by throwing a newly born kitten or puppy into the water. The same may be said of the greater number of birds. This is accounted for by the fact that quadrupeds and birds are lighter, bulk for bulk, than water, but more especially, because in walking and running the movements made by their extremities are precisely those required in swimming. They have nothing to learn, as it were. They are buoyant naturally, and if they move their limbs at all, which they do instinctively, they swim of necessity. It is different with man. The movements made by him in walking and running are not those made by him in swimming; neither is the position resorted to in swimming that which characterizes him on land. The vertical position is not adapted for water, and, as a consequence, he requires to abandon it and assume a horizontal one; he requires, in fact, to throw himself flat upon the water, either upon his side, or upon his dorsal or ventral aspect. This position assimilates him to the quadruped and bird, the fish, and everything that swims; the trunks of all swimming animals, being placed in a prone position. Whenever the horizontal position is assumed, the swimmer can advance in any direction he pleases. His extremities are quite free, and only require to be moved in definite directions to produce definite results. The body can be propelled by the two arms, or the two legs; or by the right arm and leg, or the left arm and leg; or by the right arm and left leg, or the left arm and right leg. Most progress is made when the two arms and the two legs are employed. An expert swimmer can do whatever he chooses in water. Thus he can throw himself upon his back, and by extending his arms obliquely above his head until they are in the same plane with his body, can float without any exertion whatever; or, maintaining the floating position, he can fold his arms upon his chest and by alternately flexing and extending his lower extremities, can propel himself with ease and at considerable speed; or, keeping his legs in the extended position and motionless, he can propel himself by keeping his arms close to his body, and causing his hands to work like sculls, so as to make figure-of-8 loops in the water. This motion greatly resembles that made by the swimming wings of the penguin. It is most effective when the hands are turned slightly upwards, and a greater or less backward thrust given each time the hands reciprocate. The progress made at first is slow, but latterly very rapid, the rapidity increasing according to the momentum acquired. The swimmer, in addition to the foregoing methods, can throw himself upon his face, and by alternately flexing and extending his arms and legs, can float and propel himself for long periods with perfect safety and with comparatively little exertion. He can also assume the vertical position, and by remaining perfectly motionless, or by treading the water with his feet, can prevent himself from sinking; nay more, he can turn a somersault in the water either in a forward or backward direction. The position most commonly assumed in swimming is the prone one, where the ventral surface of the body is directed towards the water. In this case the anterior and posterior extremities are simultaneously flexed and drawn towards the body slowly, after which they are simultaneously and rapidly extended. The swimming of the frog conveys an idea of the movement.[51] In ordinary swimming, when the anterior and posterior extremities are simultaneously flexed, and afterwards simultaneously extended, the hands and feet describe four ellipses; an arrangement which, as explained, increases the area of support furnished by the moving parts. The ellipses are shown at fig. 38; the continuous lines representing extension, the dotted lines flexion.