the anterior extremities (which they unquestionably are), it is not
surprising that in them the spiral rotatory movements which are
traceable in the extremities of quadrupeds, and so fully developed
in the wings of bats and birds, should be clearly foreshadowed. “The
muscles of the pectoral fins,” remarks Professor Owen, “though, when
compared with those of the homologous members in higher vertebrates,
they are very small, few, and simple, yet suffice for all the
requisite movements of the fins--elevating, depressing, advancing,
and again laying them prone and flat, by an oblique stroke, upon the
sides of the body. The rays or digits of both pectorals and ventrals
(the homologues of the posterior extremities) can be divaricated
and approximated, and the intervening webs spread out or folded
up.”--_Op. cit._ vol. i. p. 252.
[46] _Vide_ “Remarks on the Swimming of the Cetaceans,” by Dr. Murie,
Proc. Zool. Soc., 1865, pp. 209, 210.
[Illustration:
FIG. 33.--The Porpoise (_Phocœna communis_). Here the tail is
principally engaged in swimming, the anterior extremities being
rudimentary, and resembling the pectoral fins of fishes. Compare with
fig. 30, p. 65.--_Original._]
[Illustration:
FIG. 34.--The Manatee (_Manatus Americanus_). In this the anterior
extremities are more developed than in the porpoise, but still the
tail is the great organ of natation. Compare with fig. 33, p. 73,
and with fig. 30, p. 65. The shape of the manatee and porpoise is
essentially that of the fish.--_Original._]
It is otherwise with the Rays, where the hands are principally
concerned in progression, these flapping about in the water very much
as the wings of a bird flap about in the air. In the beaver, the tail
is flattened from above downwards, as in the foregoing mammals, but in
swimming it is made to act upon the water laterally as in the fish. The
tail of the bird, which is also compressed from above downwards, can be
twisted obliquely, and when in this position may be made to perform the
office of a rudder.
[Illustration:
FIG. 35.--Skeleton of the Dugong. In this curious mammal the anterior
extremities are more developed than in the manatee and porpoise,
and resemble those found in the seal, sea-bear, and walrus. They
are useful in balancing and turning, the tail being the effective
instrument of propulsion. The vertebral column closely resembles
that of the fish, and allows the tail to be lashed freely about in a
vertical direction. Compare with fig. 29, p. 65.--(After Dallas.)]
_Swimming of the Seal, Sea-Bear, and Walrus._--In the seal, the
anterior and posterior extremities are more perfect than in the whale,
porpoise, dugong, and manatee; the general form, however, and mode of
progression (if the fact of its occasionally swimming on its back be
taken into account), is essentially fish-like.
[Illustration:
FIG. 36.--The Seal (_Phoca fœtida_, Müll.), adapted principally for
water. The extremities are larger than in the porpoise and manatee.
Compare with figs. 33 and 34, p. 73.--_Original._]
A peculiarity is met with in the swimming of the seal, to which I think
it proper to direct attention. When the lower portion of the body
and posterior extremities of these creatures are flexed and tilted,
as happens during the back and least effective stroke, the naturally
expanded feet are more or less completely closed or pressed together,
in order to diminish the extent of surface presented to the water,
and, as a consequence, to reduce the resistance produced. The feet are
opened to the utmost during extension, when the more effective stroke
is given, in which case they present their maximum of surface. They
form powerful propellers, both during flexion and extension.
The swimming apparatus of the seal is therefore more highly
differentiated than that of the whale, porpoise, dugong, and manatee;
the natatory tail in these animals being, from its peculiar structure,
incapable of lateral compression.[47] It would appear that the
swimming appliances of the seals (where the feet open and close as in
swimming-birds) are to those of the sea-mammals generally, what the
feathers of the bird’s wing (these also open and close in flight) are
to the continuous membrane forming the wing of the insect and bat.
[47] In a few instances the caudal fin of the fish, as has been
already stated, is more or less pressed together during the back
stroke, the compression and tilting or twisting of the tail taking
place synchronously.
The anterior extremities or flippers of the seal are not engaged in
swimming, but only in balancing and in changing position. When so
employed the fore feet open and close, though not to the same extent
as the hind ones; the resistance and non-resistance necessary being
secured by a partial rotation and tilting of the flippers. By this
twisting and untwisting, the narrow edges and broader portions of the
flippers are applied to the water alternately. The rotating and tilting
of the anterior and posterior extremities, and the opening and closing
of the hands and feet in the balancing and swimming of the seal, form a
series of strictly progressive and very graceful movements. They are,
however, performed so rapidly, and glide into each other so perfectly,
as to render an analysis of them exceedingly difficult.
In the Sea-Bear (_Otaria jubata_) the anterior extremities attain
sufficient magnitude and power to enable the animal to progress by
their aid alone; the feet and the lower portions of the body being
moved only sufficiently to maintain, correct, or alter the course
pursued (fig. 73). The anterior extremities are flattened out, and
greatly resemble wings, particularly those of the penguin and auk,
which are rudimentary in character. Thus they have a thick and
comparatively stiff anterior margin; and a thin, flexible, and more
or less elastic posterior margin. They are screw structures, and when
elevated and depressed in the water, twist and untwist, screw-fashion,
precisely as wings do, or the tails of the fish, whale, dugong, and
manatee.
[Illustration:
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]
[48] The unusual opportunities afforded by this unrivalled collection
have enabled me to determine with considerable accuracy the movements
of the various land-animals, as well as the motions of the wings and
feet of birds, both in and out of the water. I have also studied
under the most favourable circumstances the movements of the otter,
sea-bear, seal, walrus, porpoise, turtle, triton, crocodile, frog,
lepidosiren, proteus, axolotl, and the several orders of fishes.
[49] This is the reverse of what takes place in flying, the anterior
or thick margins of the wings being invariably _directed upwards_.
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.
[50] The air-bladder is wanting in the dermopteri, plagiostomi, and
pleuronectidæ.--Owen, _op. cit._ p. 255.
_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.
[51] The frog in swimming leisurely frequently causes its extremities
to move diagonally and alternately. When, however, pursued and
alarmed, it folds its fore legs, and causes its hind ones to move
simultaneously and with great vigour by a series of sudden jerks,
similar to those made by man when swimming on his back.
[Illustration: Fig. 38.]
[Illustration: Fig. 39.]
[Illustration: Fig. 40.]
Thus when the arms and legs are pushed away from the body, the arms
describe the inner sides of the ellipses (fig. 38, _a a_), the legs
describing the outer sides (_c c_). When the arms and legs are drawn
towards the body, the arms describe the outer sides of the ellipses (_b
b_), the legs describing the inner sides (_d d_). As the body advances,
the ellipses are opened out and loops formed, as at _e e_, _f f_ of
fig. 39. If the speed attained is sufficiently high, the loops are
converted into waved lines, as in walking and flying.--(_Vide_ _g g_,
_h h_ of fig. 40, p. 81, and compare with fig. 18, p. 37, and figs. 71
and 73, p. 144.) The swimming of man, like the walking, swimming, and
flying of animals, is effected by alternately flexing and extending the
limbs, as shown more particularly at fig. 41, _A_, _B_, _C_.
[Illustration:
FIG. 41.--_A_ shows the arms and legs folded or flexed and drawn
towards the mesial line of the body.--_Original._
_B_ shows the arms and legs opened out or extended and carried away
from the mesial line of the body.--_Original._
_C_ shows the arms and legs in an intermediate position, _i.e._ when
they are neither flexed nor extended. The arms and legs require to be
in the position shown at _A_ before they can assume that represented
at _B_, and they require to be in the position shown at _B_ before
they can assume that represented at _C_. When the arms and legs are
successively assuming the positions indicated at _A_, _B_, and _C_,
they move in ellipses, as explained.--_Original._]
By alternately flexing and extending the limbs, the angles made by
their several parts with each other are decreased and increased,--an
arrangement which diminishes and augments the degree of resistance
experienced by the swimming surfaces, which by this means are made to
elude and seize the water by turns. This result is further secured by
the limbs being made to move more slowly in flexion than in extension,
and by the limbs being made to rotate in the direction of their length
in such a manner as to diminish the resistance experienced during the
former movement, and increase it during the latter. When the arms are
extended, the palms of the hands and the inner surfaces of the arms
are directed downwards, and assist in buoying up the anterior portion
of the body. The hands are screwed slightly round towards the end of
extension, the palms acting in an outward and backward direction
(fig. 41, _B_). In this movement the posterior surfaces of the arms
take part; the palms and posterior portions of the arms contributing to
the propulsion of the body. When the arms are flexed, the flat of the
hands is directed downwards (fig. 41, _C_). Towards the end of flexion
the hands are slightly depressed, which has the effect of forcing the
body upwards, and hence the bobbing or vertical wave-movement observed
in the majority of swimmers.[52]
[52] The professional swimmer avoids bobbing, and rests the side of
his head on the water to diminish its weight and increase speed.
During flexion the posterior surfaces of the arms act powerfully as
propellers, from the fact of their striking the water obliquely in a
backward direction. I avoid the terms _back_ and _forward_ strokes,
because the arms and hands, so long as they move, support and propel.
There is no period either in extension or flexion in which they are not
effective. When the legs are pushed away from the body, or extended
(a movement which is effected rapidly and with great energy, as shown
at fig. 41, _B_), the soles of the feet, the anterior surfaces of the
legs, and the posterior surfaces of the thighs, are directed outwards
and backwards. This enables them to seize the water with great avidity,
and to propel the body forward. The efficiency of the legs and feet
as propelling organs during extension is increased by their becoming
more or less straight, and by their being moved with greater rapidity
than in flexion; there being a general back-thrust of the limbs as a
whole, and a particular back-thrust of their several parts.[53] In this
movement the inner surfaces of the legs and thighs act as sustaining
organs and assist in floating the posterior part of the body. The
slightly inclined position of the body in the water, and the forward
motion acquired in swimming, contribute to this result. When the legs
and feet are drawn towards the body or flexed, as seen at fig. 41, _C_,
_A_, their movements are slowed, an arrangement which reduces the
degree of friction experienced by the several parts of the limbs when
they are, as it were, being drawn off the water preparatory to a second
extension.
[53] The greater power possessed by the limbs during extension, and
more especially towards the end of extension, is well illustrated by
the kick of the horse; the hind feet dealing a terrible blow when
they have reached their maximum distance from the body. Ostlers are
well aware of this fact, and in grooming a horse keep always very
close to his hind quarters, so that if he does throw up they are
forced back but not injured.
There are several grave objections to the ordinary or old method of
swimming just described. _1st_, The body is laid prone on the water,
which exposes a large resisting surface (fig. 41, _A_, _B_, _C_,
p. 82). _2d_, The arms and legs are spread out on either side of the
trunk, so that they are applied very indirectly as propelling organs
(fig. 41, _B_, _C_). _3d_, The most effective part of the stroke of the
arms and legs corresponds to something like a quarter of an ellipse,
the remaining three quarters being dedicated to getting the arms and
legs into position. This arrangement wastes power and greatly increases
friction; the attitudes assumed by the body at _B_ and _C_ of fig. 41
being the worst possible for getting through the water. _4th_, The arms
and legs are drawn towards the trunk the one instant (fig. 41, _A_),
and pushed away from it the next (fig. 41, _B_). This gives rise to
dead points, there being a period when neither of the extremities are
moving. The body is consequently impelled by a series of jerks, the
swimming mass getting up and losing momentum between the strokes.
In order to remedy these defects, scientific swimmers have of late
years adopted quite another method. Instead of working the arms and
legs together, they move first the arm and leg of one side of the body,
and then the arm and leg of the opposite side. This is known as the
_overhand_ movement, and corresponds exactly with the natural walk of
the giraffe, the amble of the horse, and the swimming of the sea-bear.
It is that adopted by the Indians. In this mode of swimming the body
is thrown more or less on its side at each stroke, the body twisting
and rolling in the direction of its length, as shown at fig. 42,
an arrangement calculated greatly to reduce the amount of friction
experienced in forward motion.
[Illustration: FIG. 42.--Overhand Swimming.--_Original._]