<h2><SPAN name="CHAPTER_IV" id="CHAPTER_IV"></SPAN><small>CHAPTER IV</small><br/><br/> ANIMALS WHICH FLY</h2>
<p>The nature of a reptile is now sufficiently intelligible
for something to be said concerning
flight, and structures by means of which some animals
lift themselves in the air. It is not without interest
to remember that, from the earliest periods in human
records, representations have been made of animals
which were furnished with wings, yet walked upon
four feet, and in their
typical aspect have the
head shaped like that of
a bird. They are commonly
named Dragons.</p>
<h4>FLYING DRAGONS</h4>
<div class="figcenter"> <SPAN name="Fig_3" id="Fig_3"></SPAN> <span class="caption">FIG. 3 From <i>The Battle between Bel and the Dragon</i></span> <ANTIMG src="images/i_032.jpg" width-obs="461" height-obs="640" alt="FIG. 3" title="FIG. 3" /></div>
<p>The effigy of the
dragon survives to the
present day in the figure
over which St. George
triumphs, on the reverse
of the British sovereign.
In the luxuriant imaginations
of ancient Eastern
peoples, dating back
<span class="pagenum"><SPAN name="Page_16" id="Page_16">[Pg 16]</SPAN></span>
to prehistoric ages, perhaps 5000 <small>B.C.</small>, the dragons
present an astonishing constancy of form. In after-times
they underwent a curious evolution, as the conception
of Babylon and Egypt is traced through
Assyria to Greece. The Wings, which had been associated
at first with the fore limb of the typical dragon,
become characteristic of the Lion, and of the poet's
winged Horse, and finally of the Human figure itself,
<span class="pagenum"><SPAN name="Page_17" id="Page_17">[Pg 17]</SPAN></span>
carved on the great columns of the Greek temples of
Ephesus. These flying animals are historically descendants
of the same common stock with the dragons
of China and Japan, which still preserve the aspect
of reptiles. Their interest is chiefly in evidence of
a latent spirit of evolution in days too remote for its
meaning to be now understood, which has carried the
winged forms higher and ever higher in grade of
organisation, till their wings ceased to be associated
with feelings of terror. The Hebrew cherubim are
regarded by H. E. Ryle, Bishop of Exeter, as probably
Dragons, and the figure of the conventional
angel is the human form of the Dragon.</p>
<div class="figcenter"> <SPAN name="Fig_4" id="Fig_4"></SPAN> <span class="caption">FIG. 4. FIGURE FROM THE TEMPLE OF EPHESUS</span> <ANTIMG src="images/i_033.jpg" width-obs="480" height-obs="636" alt="FIG. 4. FIGURE FROM THE TEMPLE OF EPHESUS" title="" /></div>
<h4>ORGANS OF FLIGHT</h4>
<p>Turning from this reference to the realm of mythology
to existing nature, the power of flight is
popularly associated with all the chief types of
vertebrate animals—fishes, frogs, lizards, birds, and
mammals. Many of the animals ill deserve the
name of flyers, and most are exceptions to different
conditions of existence which control their kindred,
but it is convenient to examine for a little the nature
of the structures by which this movement in the air,
which is not always flight, is made possible. Certain
fishes, like the lung-fish Ceratodus, of Queensland,
and the mud-fish Lepidosiren, are capable of leaving
the water and living on land, and for a time breathe
air. But neither these fishes nor Periophthalmus,
which runs with rapid movement of its fins and
carries the body more or less out of water, or the
climbing perch, Anabas, carried out of water over
the country by Indian jugglers, ever put on the
slightest approach to wings.</p>
<p><span class="pagenum"><SPAN name="Page_18" id="Page_18">[Pg 18]</SPAN></span></p>
<h4>FLYING FISHES</h4>
<div class="figcenter"> <SPAN name="Fig_5" id="Fig_5"></SPAN> <span class="caption">FIG. 5. THE FLYING FISH EXOCŒTUS</span> <p class="center">With the fins extended moving through the air</p> <ANTIMG src="images/i_035.jpg" width-obs="640" height-obs="365" alt="FIG. 5." title="FIG. 5." /></div>
<p>The flight of fishes is a kind of parachute support
not unlike that by which a folded paper is made to
travel in the air. It is chiefly seen in the numerous
species of a genus Exocœtus, allied to the gar-pike
(Belone), which is common in tropical seas, and
usually from a foot to eighteen inches long. They
emerge from the water, and for a time support themselves
in the air by means of the greatly developed
breast fins, which sometimes extend backward to the
tail fin. Although these fins appear to correspond
to the fore limbs of other animals, they may not
be moved at the will of the fish like the wing of a
bird. When the flying fishes are seen in shoals in
the vicinity of ships, those fins remain extended, so
that the fish is said sometimes to travel 200 yards
at a speed of fifteen miles an hour, rising twenty feet
or more above the surface of the sea, travelling in
a straight line, though sometimes influenced by the
wind. Here the organ, which is at once a fin and a<span class="pagenum"><SPAN name="Page_19" id="Page_19">[Pg 19]</SPAN></span>
wing, consists of a number of thin long rods, or rays,
which are connected by membrane, and vary in
length to form an outline not unlike the wing of a
bird which tapers to a point. The interest of these
animals is chiefly in the fact that flight is separated
from the condition of having lungs with which it
is associated in birds, for although the flying fish has
an air bladder, there is no duct to connect it with
the throat.</p>
<h4>FLYING FROGS</h4>
<div class="figcenter"> <SPAN name="Fig_6" id="Fig_6"></SPAN> <span class="caption">FIG. 6. THE FLYING FROG (RHACOPHORUS)</span> <ANTIMG src="images/i_036.jpg" width-obs="480" height-obs="548" alt="FIG. 6." title="FIG. 6." /> <p class="center">The membranes of the foot and
hand extend between the metatarsal
and metacarpal bones, as well as the
bones of the digits.</p>
</div>
<p>Among amphibians the organs of flight are also
of a parachute kind, but of a different nature. They
are seen in certain frogs which
frequent trees, and are limited
to membranes which extend
between the diverging digits
of the hand and foot, forming
webs as fully developed as in
the foot of a swimming bird.
As these frogs leap, the membranes
are expanded and help
to support the weight of the
body, so that the animal descends
more easily as it moves
from branch to branch. There
is no evidence that the bones
of the digits ever became elongated like the fin rays
of the flying fish or the wing bones of a Bat; but
the web suggests the basis of such a wing, and the
possibilities under which wings may first originate,
by elongation of the bones of a webbed hand like
that of a Flying Frog.</p>
<p><span class="pagenum"><SPAN name="Page_20" id="Page_20">[Pg 20]</SPAN></span></p>
<h4>FLYING LIZARDS</h4>
<p>The Reptilia in their several orders are remarkable
for absence of any modification of the arms which
might suggest a capacity for acquiring wings, as
being latent in their organisation. Crocodiles, Tortoises,
and Serpents are alike of the earth, and not
of the air. But among Lizards there are small groups
of animals in which a limited capacity for
movement through the air is developed.
It is best known in the family of small
lizards named Dragons, represented typically
by the species <i>Draco volans</i> found in the Oriental
region of the East Indies and Malay Archipelago.</p>
<div class="figcenter"> <SPAN name="Fig_7" id="Fig_7"></SPAN> <span class="caption">FIG. 7. THE FLYING DRAGON, DRACO</span> <p class="center">Forming a parachute by means of the extended ribs</p> <ANTIMG src="images/i_037.jpg" width-obs="620" height-obs="480" alt="FIG. 7." title="FIG. 7." /></div>
<p>The organ of flight is produced in an unexpected
way, by means of the ribs instead of the limbs. The
ribs extend outward as far as the arms can stretch,
and the first five or six are prolonged beyond the
body so as to spread a fold of skin on each side
between the arm and the leg. The membrane admits<span class="pagenum"><SPAN name="Page_21" id="Page_21">[Pg 21]</SPAN></span>
of some movement with the ribs. This arrangement
forms a parachute, which enables the animal to move
rapidly among branches of trees, extending the structure
at will, so that it is used with rapidity too quick
to be followed by the eye, as it leaps through considerable
distances.</p>
<p>A less singular aid to movement in the air is found
in some of the lizards termed Geckos. The so-called
Flying Gecko (<i>Platydactylus homalocephalus</i>) has a
fringe unconnected with ribs, which extends laterally
on the sides of the body and tail, as well as at the
back and front of the fore and hind limbs, and between
the digits, where the web is sometimes almost as
well developed as among Tree Frogs. This is essentially
a lateral horizontal frill, extending round the
body. Its chief interest is in the circumstance that it
includes a membrane which extends between the wrist
bones and the shoulder on the front of the arm. That
is the only part of the fringe which represents the wing
membrane of a bird. The fossil flying reptiles have
not only that membrane, but the lateral membranes
at the sides of the body and behind the arms.</p>
<p>Other lizards have the skin developed in the
direction of the circumference of the body. In the
Australian Chlamydosaurus it forms an immense
frill round the neck like a mediæval collar. But
though such an adornment might break a fall, it
could not be regarded as an organ of flight.</p>
<h4>FLYING BIRDS</h4>
<p>The wings of birds, when they are developed so as
to minister to flight, are all made upon one plan; but
as examples of the variation which the organs contributing
to make the fore limb manifest, I may
<span class="pagenum"><SPAN name="Page_22" id="Page_22">[Pg 22]</SPAN></span>
instance the short swimming limb of the Penguin,
the practically useless rudiment of a wing found in
the Ostrich or Kiwi, and the fully developed wing of
the Pigeon. The wings of birds obtain an extensive
surface to support the animal by muscular movements
of three modifications of structure. First, the bones
of the fore limb are so shaped that they cannot, in
existing birds, be applied to the ground for support
and be used like the limbs of quadrupeds, and are
therefore folded up at the sides of the body, and<span class="pagenum"><SPAN name="Page_23" id="Page_23">[Pg 23]</SPAN></span>
carried in an unused or useless state so long as the
animal hops on the ground or walks, balancing its
weight on the hind legs. Secondly, there are two
small folds of skin, less conspicuous than those on
the arms of Geckos; one is between the wrist bones
and the shoulder, and the smaller hinder membrane
is between the upper arm and the body. These
membranous expansions are insignificant, and would
in themselves be inadequate to support the body or
materially assist its movements. Thirdly, the bird
develops appendages to the skin which are familiarly
known as feathers, and the large feathers which make
the wing are attached to the skin covering the lower
arm bone named the ulna, and the other bones which
represent the wrist and hand. The area and form of
the bird's wing are due to individual appendages to
the skin, which are unknown in any other group of
animals. Between the extended wing of the Albatross,
measuring eleven feet in spread, and the condition
in the Kiwi of New Zealand, in which the
wing is vanishing, there is every possible variation in
size and form. As a rule, the larger the animal the
smaller is the wing area. The problem of the origin
of the bird's wing is not to be explained by study of
existing animals; for the rowing organ of the Penguin,
which in itself would never suggest flight,
becomes an organ of flight in other birds by the
growth upon it of suitable feathers. Anyone who
has seen the birds named Divers feeding under water,
swimming rapidly with their wings, might never
suspect that they were also organs of aerial flight.
The Ostrich is even more interesting, for it has not
developed flight, and still retains at the extremities
of two of the digits the slender claws of a limb
which was originally no wing at all, but the support
of a four-footed animal (<SPAN href="#Fig_46">Fig. 46, p. 130</SPAN>).</p>
<div class="figcenter"> <SPAN name="Fig_8" id="Fig_8"></SPAN> <span class="caption">FIG. 8. POSITION OF BIRDS IN FLIGHT</span> <ANTIMG src="images/i_039.jpg" width-obs="480" height-obs="481" alt="FIG. 8. POSITION OF BIRDS IN FLIGHT" title="FIG. 8." /></div>
<p><span class="pagenum"><SPAN name="Page_24" id="Page_24">[Pg 24]</SPAN></span></p>
<h4>FLYING MAMMALS</h4>
<p>Flight is also developed among mammals. The
Insectivora include several interesting examples of
animals which are capable of a certain motion through
the air. In the tropical forests of the Malay Archipelago
are animals known as Flying Squirrels, Flying
Opossums, Flying Lemurs, Flying
Foxes, in which the skin extends
outward laterally from the sides
of the body so as to connect the
fore limbs with the hind limbs,
and is also prolonged backward
from the hind limbs to the tail.
The four digits are never elongated;
the bones of the fore limb
are neither longer nor larger than
those of the hind limb, and the
foot terminates in five little claws
as in other four-footed animals.
This condition is adapted for the arboreal life which
those animals live, leaping from branch to branch,
feeding on fruits and leaves, and in some cases
upon insects. These mammals may be compared
with the Flying Geckos among reptiles in their
parachute-like support by extension of the skin,
which gives them one of the conditions of support
which contribute to constitute flight.</p>
<div class="figcenter"> <SPAN name="Fig_9" id="Fig_9"></SPAN> <span class="caption">FIG. 9. FLYING SQUIRREL (PTEROMYS)</span> <ANTIMG src="images/i_041.jpg" width-obs="423" height-obs="640" alt="FIG. 9." title="FIG. 9." /></div>
<p><i>Bats.</i>—One entire order of mammals—the Bats—not
only possess true wings, but are capable of flight
which is sustained, and in some cases powerful. The
wings are clothed with short hair like the rest of the
<span class="pagenum"><SPAN name="Page_25" id="Page_25">[Pg 25]</SPAN></span>
body, and thus the instrument of flight is unlike that
of a bird. The flight of a Bat differs from that
of all other animals in being dependent upon a
modification of the bones of the fore limb, which,
without interfering with the animal's movements as
a quadruped, secures an extension of the wing which
is not inferior in area to that which the bird obtains
by elongation of the bones of the arm and fore-arm
and its feathers. The distinctive peculiarity of the
Bat's wing is in the circumstance that four of the
digits of the hand have their bones prolonged to
a length which is often equal to the combined length
of the arm and fore-arm. The bones of the digits<span class="pagenum"><SPAN name="Page_26" id="Page_26">[Pg 26]</SPAN></span>
diverge like the ribs of an umbrella, and between
them is the wing membrane, which extends from the
sides of the body outward, unites the fore limb with
the hind limb, and is prolonged down the tail as
in the Flying Foxes. Bats have a small membrane
in front of the bones of the arm and fore-arm
stretching between the shoulder and the wrist, which
corresponds with the wing membrane of a bird; but
the remainder of the membranes in Bats' wings are
absent in birds, because their function is performed
by feathers which give the wing its area. The
elongated digits of the Bat's wing are folded together
and carried at the sides of the body as though they
were a few quill pens attached to its wrist, where the
one digit, which is applied to the ground in walking,
terminates in a claw.</p>
<div class="figcenter"> <SPAN name="Fig_10" id="Fig_10"></SPAN> <span class="caption">FIG. 10 NEW ZEALAND BAT FLYING. BARBASTELLE WALKING</span> <ANTIMG src="images/i_042.jpg" width-obs="551" height-obs="480" alt="FIG. 10" title="FIG. 10" /></div>
<p>The organs which support animals in the air are
thus seen to be more or less dissimilar in each of the
great groups of animals. They fall into three chief
types: first, the parachute; secondly, the wing due
to the feathers appended to the skin; and thirdly, the
wing formed of membrane, supported by enormous
elongation of the small bones of the back of the
hand and fingers. The two types of true wings are
limited to birds and bats; and no living reptile
approximates to developing such an organ of flight
as a wing. Judged, therefore, by the method of comparing
the anatomical structures of one animal with
another, which is termed "comparative anatomy," the
existence of flying reptiles might be pronounced
impossible. But in the light which the revelations
of geology afford, our convictions become tempered
with modesty; and we learn that with Nature nothing
is impossible in development of animal structure.</p>
<hr style="width: 65%;" />
<p><span class="pagenum"><SPAN name="Page_27" id="Page_27">[Pg 27]</SPAN></span></p>
<div style="break-after:column;"></div><br />
1 of 2
2 of 2
Previous
Next
Update Required
To play the media you will need to either update your browser to a recent version or update your Flash plugin.