1125. _Why can gossamer spiders float through the air?_
Because, having no wings, and being deficient in the active muscular
powers of other spiders, they have been endowed with the power of
spinning a web which is so light that it floats in the air, and bears
the body of the gossamer spider from place to place. Each web acts as a
balloon, and the spider attached thereto is a little _aeronaut_.
1126. _Why do crickets make a peculiar chirping sound?_
Because they have hard wing cases, by the friction of the edges of
which they cause their peculiar noise, _to make known to each other
where they are_, in the dark crevices in which they hide.
[Illustration: Fig. 74.--GLOW-WORM USING HIS BRUSH.]
1127. _Why has the glow-worm a brush attached to its tail?_
Because it is necessary to keep its back very clean, that _the light
which its body emits may not be dimmed_.
1128. _Why does the glow-worm emit a light?_
Because the female glow-worm is without wings, but the male is a winged
insect. The female, therefore, is endowed with the power of displaying
a phosphorescent light. The light is only visible by night, but it is,
nevertheless, beautifully adapted for the purpose stated, because the
_male is a night-flying insect_, and never ventures abroad by day.
[Verse: "They that go down to the sea in great ships, that do
business in great waters these see the works of the Lord, and his
wonders in the deep."--PSALM CVII.]
There exists some difference of opinion between naturalists upon
the uses of the light of a glow-worm; there are some who doubt
that it is exhibited to attract the flying insect. The objectors,
however, offer no explanation of the luminous properties of the
worm. Sir Charles Bell says the preponderance of the argument is
decidedly in favour of the explanation we have given.
1129. _Why does not the iris of the fish's eye contract_?
Because the diminished light in water is _never too strong for the
retina_.
1130. _Why is the eye of the eel covered with a transparent horny
covering?_
Because, as the eel lives in holes, and pushes its head into mud, and
under stones, &c., it needed such a covering to _defend the eye_.
1131. _Why is the whale provided with an eye, having remarkably thick
and strong coats?_
Because, when he is attacked by the sword-fish and the shark, he is
almost helpless against his enemies, as they fix themselves upon his
huge carcase. He therefore dives with them down to a depth where the
pressure of the water is so great that they cannot bear it. The eye
of the whale is expressly organised _to bear the immense pressure of
extreme ocean depths_, without impairing the sight.
1132. _Why have fishes no eyelids?_
Because the water in which they swim keeps their eyes moist. Eyelids
would therefore be _useless to them_.
1133. _Why have fishes the power of giving their eye-balls very sudden
motion?_
Because, having no eyelids (such organs being unnecessary to keep their
eyes moist), they still need the power of freeing their eyes from the
contact of foreign matters; and this is secured to them by the power
they have of giving the eyeball a very rapid motion, which causes
reaction in the fluid surrounding it, and _sweeps the surface_.
This motion may frequently be seen in the eyes of fishes, in glass
globes.
[Verse: "And God made the beast of the earth after his kind, and
cattle after their kind, and everything that creepeth upon the earth
after his kind: and God saw that it was good."--GENESIS I.]
1134. _Why is the lachrymal secretion of the horse's eye thick and
glutinous?_
Because, as his eye is large, and constantly exposed to dust on
journeys, it is provided with a _viscid secretion_, which cleanses the
eye, and more instantly and securely removes the dust, than a _watery_
secretion would.
1135. _Why does the lower bill of the sea-crow project beyond the upper
one?_
Because the bird obtains his food by _skimming along the water_, into
which he dips his bill, and lifts his food out.
1136. _Why do the mandibles of the cross-bill overlap each other?_
Because the bird requires a peculiar bill, to enable it to _split seeds
into halves_, and to tear the open cones of the fir-tree.
1137. _Why are the tails of fishes so much larger than their fins?_
Because their tails are their _chief instruments of motion_, while
their fins are employed simply to direct their progress, and steady
their movements.
1138. _Why have oxen, and other quadrupeds a tough ligament called the
"pax-wax," running from their backs to their heads?_
Because their heads are of considerable weight; and having frequent
occasion to lift them, they are provided with an elastic ligament,
which is fastened at the middle of their backs, while its other
extremity is attached to the head. This enables them to raise their
heads easily; otherwise the effort to do so would be a work of great
labour. To the horse, the pax-wax acts as a natural bearing-rein,
assisting it to hold its head in that position which adds to the grace
and beauty of the animal.
In carving beef, this ligament may be seen passing along the
vertebræ of the neck, the chuck, and the fore ribs.
[Verse: "He shall feed his flock like a shepherd; he shall gather
the lambs with his arm, and carry them in his bosom, and shall gently
lead those that are with young."--ISAIAH XL.]
1139. _Why have the females of the kangaroo and opossum tribes pouches,
or pockets, formed in the skin of their breasts for the reception of
their young?_
Because their young ones are remarkably _small and helpless_; in fact,
more so than those of any other animal of equal proportions. Besides
which, the full grown animals have very long hind-legs, and they
progress by a series of extraordinary leaps. It would consequently
be impossible for their helpless young ones to follow them: God has
therefore given to female kangaroos and opossums curious pockets,
_formed out of their own skin_, in which they place their little young
ones, and bear them through their surprising leaps with the greatest
ease and safety.