1052. _Why have birds with long legs short tails?_
Because the tails of birds are used to guide them through the air, by
a _kind of steerage_. When birds with long legs take to flight, they
throw their legs behind, and they then _serve the same purpose as a
tail_.
[Illustration: Fig. 68.--PERCH.]
1053. _Why have fishes fins?_
The fins of fishes are to them, _what wings and tails are to birds_,
enabling them to rise in the fluid in which they live by the _reaction
of the motions of the fins upon its substance_.
[Verse: "Speak to the earth, and it shall teach thee; and the fishes
of the sea shall declare unto thee. Who knoweth not in all these that
the hand of the Lord hath wrought this."--JOB XII.]
1054. _Why are the fins of fishes proportionately so much smaller than
the wings of birds?_
Because there is less difference between the _specific gravity_ of the
body of a fish, and the water in which it moves, than between the body
of a bird, and the air on which it flies. The fish, therefore _does not
require such an expanded surface to elevate or guide it_.
1055. _Why have fishes scales?_
Because scales, while they afford protection to the bodies of fish,
are conveniently adapted to their motions; and as the scales _present
no surface to obstruct their passage through the water_, as hair or
feathers would do, they evidently form the best covering for the
aquatic animal.
1056. _Why do fishes float in streams (when they are not swimming) with
their heads towards the stream?_
Because they _breathe_ by the transmission of water over the surface
of their gills, the water entering at the mouth, and passing over the
gills behind. When, therefore, they lie motionless with their heads to
the stream, they are in _that position which naturally assists their
breathing process_.
1057. _Why have fishes air-bladders?_
Because, as the density of water varies greatly at different depths,
the enlargement or contraction of the bladder regulates the relation of
_the specific gravity of the body of the fish to that of the water in
which it moves_.
1058. _Why have whales a very large development of oily matter about
their heads?_
Because their heads are thereby rendered the lighter part of their
bodies, and a very slight exertion on the part of the animal will bring
its head to the surface _to breathe air, which it constantly requires_.
1059. _Why have birds that swim upon water web-feet?_
Because the spreading out of the toes of the bird brings the membrane
between the toes into the form of a fin, or _water-wing_, by striking
which against the water, _the bird propels itself along_.
[Verse: "And Jesus saith unto him, The foxes have holes, and the
birds of the air have nests; but the son of man hath not where to lay
his head."--MATTHEW XIII.]
1060. _Why have birds that swim and dive short legs?_
Because long legs would greatly _impede their motions in the water_, by
becoming repeatedly entangled in the weeds, and by striking against the
bottom. _Waders_, however, require long legs because they have to move
about through the _tall vegetation of marshy borders_.
[Illustration: Fig. 69.--STILT-PLOVER AND DUCK.]
1061. _Why have the feet of the heron, cormorant, &c., deep rough
notches upon their under surface?_
Because, as those birds live by catching fish, they are enabled by the
notches in their feet, to _hold the slippery creatures upon which they
feed_.
1062. _Why have otters, seals, &c., web-feet?_
Because, while the feet enable them to _walk upon the land_, they are
equally effective in their action upon the water, and hence they are
_adapted to the amphibious nature of the animals to which they belong_.
1063. _Why do the external ears of animals of prey, such as cats,
tigers, foxes, wolves, hyenas, &c., bend forward?_
Because they collect the sounds that occur _in the direction of the
pursuit_, and enable the animal to _track its prey_ with greater
certainty.
[Verse: "Doth the hawk fly by thy wisdom, and stretch her wings
toward the south? "Doth the eagle mount up at thy command, and make her
nest on high?"]
1064. _Why do the ears of animals of flight, such as hares, rabbits,
deer, &c., turn backward?_
Because they thereby catch the sounds that give them _warning of the
approach of danger_.
1065. _Why has the stomach of the camel a number of distinct bags, like
so many separate stomachs?_
Because water is stored up in the separate chambers of the stomach,
apart from the solid aliment, so that the animal can _feed_, without
consuming all its drink. It is thereby _able to retain water to satisfy
its thirst while travelling across hot deserts_, where no water could
be obtained.
1066. _Why do woodpeckers "tap" at old trees?_
Because by boring through the decayed wood, with the sharp and hard
bills with which they are provided, _they get at the haunts of the
insects upon which they feed_.
1067. _Why are woodpeckers' tongues about three times longer than their
bills?_
Because, if their bills were long, they would not bore the trees so
efficiently; and when the trees are bored, and the insects alarmed,
they endeavour to retreat into the hollows of the wood; _but the long
thin tongue of the woodpecker fixes them on its sharp horny point_, and
draws them into the mouth of the bird.
1068. _Why have the Indian hogs large horns growing from their nostrils
and turning back towards their eyes?_
Because the horns _serve as a defence to the eyes_ while the animal
forces its way through the thick underwood in which it lives.
1069. _Why have calves and lambs, and the young of horned cattle
generally, no horns while they are young?_
Because the presence of horns would _interfere with the suckling
of the young animal_. When, however, it is able to feed itself by
browsing, _then the horns begin to grow_.
[Verse: "She dwelleth and abideth on the rock, upon the crag of the
rock, and the strong place.
"From thence she seeketh the prey, and her eyes behold afar off. Her
young ones also suck up blood: and where the slain are, there is
she."--JOB XXXIX.]
1070. _Why have infants no teeth?_
Because the presence of teeth would interfere with their suckling,
while the teeth would be of no service, until the child _could take
food requiring mastication_.
1071. _Why cannot flesh-eating animals live upon vegetables?_
Because the gastric juice of a flesh-eating animal, being adapted to
the duty which it has to perform, _will not dissolve vegetable matter_.
1072. _Why have birds gizzards?_
Because, having no teeth, the tough and fibrous gizzards are employed
_to grind the food preparatory to digestion_.
1073. _Why are small particles of sand, stone, &c., found in the
gizzards of birds?_
Because, by the presence of those rough particles, which become
embedded in the substance of the gizzard, the food of the bird is more
effectively ground.
When our fowls are abundantly supplied with meat, they soon fill
their craw, but it does not immediately pass thence into the
gizzard; it always enters in small quantities, in proportion
to the progress of trituration, in like manner, as in a mill,
a receiver is fixed above the two large stones which serve for
grinding the corn, which receiver, although the corn be put
into it by bushels, allows the grain to dribble only in small
quantities into the central hole in the upper mill-stone.--_Paley._