“mantle”, except for a muscular, stalk-like extension, the peduncle, by
which it attaches itself to the sea bottom. Inside the shell, folded
around the mouth when the animal is at rest, are two arms or tentacles
with which it can probe the water and obtain minute food particles. It
also apparently breathes through these tentacles, which have a rapid
blood circulation.
Most numerous of the extant brachiopods is a curious animal, the
lingula, which is nearly world-wide in distribution and whose peduncle
is used for food in both Japan and the Philippine Islands. Along the
Atlantic coast it is present from Chesapeake Bay to Florida. It makes
a nearly vertical burrow in mud or sand from two to twelve inches
deep—within which it lives, attached to the bottom by the peduncle.
On this footlike appendage it can lift itself until the front part of
the shell-enclosed portion of the body is above the surface. This is
withdrawn into the burrow instantly on the slightest alarm. The animal
apparently has a quite sensitive, although very primitive, nervous
system.
The extant brachiopods are usually small animals but in their Permian
heyday some attained a length of more than six inches. For essentially
200,000,000 years they were without much competition in the mud burrows
to which they had resorted. During this time arose clams, sea snails,
and other mollusks which were free to move about and competed with them
for the available food supply. The brachiopod was unable to meet this
vigorous competition and in a few million years the race was well on
its way towards extinction. Most species disappeared. A few, including
the Lingula, survived into the age of the great dinosaurs, and their
descendants constitute the species living today. They are now obscure
creatures and a poverty-stricken group compared to their ancestors.
In the Permian seas they had surplus energy to expend not only in
variation of form and habit—but in shell artistry. Some of the
specimens obtained by the Smithsonian paleontologists are like
glittering gems surrounded by silvery, hair-like spines.
These spiny brachiopods constitute about two-thirds of all the fossils
obtained from the Glass Mountain rocks. Although the most abundant they
were far from the dominant animals of the Permian sea. They always were
defenseless little creatures, dependent on their hard, spiny shells
for protection. The sea monsters of the day, creatures related to the
present chambered nautilus and some of which were nearly two feet in
diameter, unquestionably were the lords of this marine creation. But
they were free-swimming predators who had little reason for concern
with the humble mud-dwellers. Next to the brachiopods in numbers and
variety, and probably their chief competitors, were the ancient lace
weavers. Both shared forests of sponges which grew like small trees,
up to heights of four feet and four to six inches across. Clams, some
of which reached the size of giants, were beginning to claim dominion
of the offshore mud and the brachiopods were near the end of their
prosperous days.
Like the sedentary worms, and most of the mollusks the brachiopod
starts life as a minute, free-swimming, wormlike larva, top-shaped
and extremely active. During this period the mortality of the tiny
unprotected creatures is very great, but once the mud-dwelling phase of
existence has started, the race is secure from most enemies.
_Feathers on Birds Adapt to the Seasons_
There is a definite seasonal variation in the number of feathers on
most birds. It amounts to a “natural adjustment in dress to the needs
of the season”. This fact has been determined through the laborious
process of actually counting the feathers of birds of the same species
at different seasons.
The number of feathers declines steadily from early spring until the
end of summer when the so-called “post-nuptial” moult takes place,
after which the bird gets a new coat to last it a year. The bulk of
the new feathers are acquired at the same time, but some are added
progressively as the weather gets colder. An exception to this is
found, however, among those birds which migrate south early. These
apparently get a complete new outfit for their journey, since they will
not be obliged to experience any noteworthy change of climate.
_Why the Dodo Became Extinct_
Smithsonian ornithologists have “rebuilt” a dodo. The dodo was a large,
pigeon-like, flightless bird which was abundant on Mauritius and
neighboring islands in the Indian ocean during the seventeenth century.
It became a symbol—first of stupidity and later of extinction.
In its restricted environment it apparently had known no serious
enemies prior to the coming of man. It had grown heavy, taken to a
ground existence, and lost the ability to fly. It showed no fear
of man and, because of its clumsy movements, was easy to catch and
slaughter, but its flesh was tough and tasteless, even for sailors who
had gone for months without fresh meat. Dutch navigators called it “the
nauseating fowl”.
Dogs brought by the sailors killed great numbers of the stupid birds.
They might have survived despite their slowness and stupidity, however,
had it not been for the pigs and Ceylonese monkeys which came to
Mauritius with the first settlers. The rooting swine destroyed the
bird’s eggs and the monkeys devoured its young. It was entirely extinct
at the start of the eighteenth century.
_The Shark of the Soil_
There is a protozoan, wormlike monster of the microscopic world, seen
only about forty times in two centuries, which gobbles up its fellow
one-celled creatures a hundred at a time, walks backwards and forwards
at once, and hunts in packs.
It is fifty times the size of the most familiar of one-celled animals,
the paramecia, which constitute the dominant population (in numbers)
of the invisible creation. It moves among the paramecia like a giant,
flesh-eating dinosaur among humans. It is a cumbersome, slow-moving
mass of protoplasm. Two or three get together and completely surround
a large school of paramecia and these are divided as meals for the
captors.
The creature was first described by the Swedish botanist Linnaeus in
1775. He called it _Chaos chaos_. It consists of a single cell, but
differs from other one-celled animals in having three cell nuclei,
instead of a single one. To reproduce, it splits in three parts, each a
new animal.
_Chaos chaos_ moves by stretching itself out into a ribbon-like form
and proceeds, by a series of tugs of war, with one end or the other
winning out. The animal supposedly is very rare and has been seen only
about once every ten years. It may be a missing link between single-and
multi-celled animals—or it may be on an entirely different evolutionary
track.
_The Sleeping Habits of Mammals_
The tiny elephant shrew (its elongated nose gives it the appearance of
a miniature elephant) apparently never closes its eyes. It is a desert
animal, continually exposed to danger, and must “see” even when it is
asleep.
Soundest sleepers are the burrowing animals, even when they take their
naps above ground. They are conditioned through innumerable generations
of safe slumber in their subterranean chambers. Sleeping pocket mice
and hamsters can be picked up without being awakened.
Sleep habits appear to be well adjusted to the needs of each species.
Most bats, for example, sleep hanging head downward, suspended by the
nails of the hind feet. This places them in a good position for sudden
flight at any alarm. They have only to let go with their toes and
spread their wings.
Curious sleepers are the armadillos. They tremble almost continually in
their sleep.
_The Eerie Eyes of Animals at Night_
Eerie lights shine in the silent blackness of the jungle night. There
are red lights and green lights, orange lights and yellow lights. They
are reflections from the eyes of all sorts of animals.
This weird phenomenon has been observed closely for some years by
Ernest P. Walker of the National Zoo in Washington. The shining of eyes
is a fairly well-known phenomenon but most of the observations have
been made in the wild. The owner of the eyes is usually unknown, and
it is virtually impossible to observe the animal again. Mr. Walker has
concentrated his observations on caged animals.
He uses a reflecting headlamp, similar to a hand flashlight, worn on
the forehead and connected with a three-cell battery in his pocket or
attached to his belt. This is necessary because the rays of reflected
light must parallel closely the line of sight of the observer.
The “shines” range in color from pale silvery through silver,
blue-green, pale gold, gold, reddish gold, brown, and amber to pink,
with a range of intensity from dull to very brilliant. The eyes of
alligators and crocodiles “give one the impression that he is looking
into a brilliantly glowing pinkish opening in a dull-surfaced bed of
coal”. Most eye shines of mammals have the appearance of coming from
highly polished metal surfaces.
“Sometimes,” explains Mr. Walker, “it is like looking into an
incandescent globe of the color indicated. Often pronounced light
rays seem to emanate from the eyes. With some eyes, such as those of
the smaller rodents, the effect is that of looking into an illuminated
piece of amber.
“In the case of animals that have eyes that glow, it appears that we
look into the eye through the pupil as if the reflection came from the
front surface of the retina. In those animals that give a reflection as
if from polished metal I gain no impression of looking into the eye. In
most cases the reflection is not obtainable closer than from eight to
twenty feet—a distance which prevents one from observing which surface
reflects. The reflection from alligators and crocodiles can be seen
when the observer is within a foot of the animal.”
Most animals stare at light, or barely move their heads. There seldom
is any “startle” response when a beam is flashed upon them. There is no
shine in the eyes of higher apes and monkeys. There have been reports
of something of the sort from human eyes, but no definite proof has
been offered. There was a faint suggestion of a reflection from the
ring-tailed lemur, a close relative of the monkey family. On the other
hand, the most brilliant eye-shine of all was from two tiny members of
the lemur tribe, the slow loris and the potto.
The majority of rodent eyes shine dully in browns, hazel or amber.
Porcupines are an exception. Their eyes are very brilliant, generally
silver and reflecting over a wide angle. Whether snakes have any true
eye reflection is questionable. Light is reflected, however, from the
surface of the scales over the eyes.
World of the Blind
There is a fifth realm of life—the wet, heavy, black darkness of
limestone caves whose chambers, ponds and streams harbor almost a
hundred species of worms, pseudo-worms, fish, insects and salamanders
which have become adapted to life in this cheerless world over millions
of generations.
Nearly all are white and blind. Blind white fish chase and eat blind
white worms. Blind white spiders spin nets to trap blind, white flies.
All are sluggish creatures. Kentucky’s Mammoth Cave alone contains
approximately 50 species. Latest to be classified scientifically are
small, rather gruesome white worms of the sort one might imagine
feeding on the dead. They live in water, clinging to the bottoms of
rocks.
Most spectacular of cave animals is the spectral Proteus, found in
limestone caves of Dalmatia, Carinthia and Carnolia in southeastern
Europe. It is a kind of salamander, related to frogs and toads. It
looks and acts like a big white worm. The creature is about a foot
long and pure white except for its gills, which are vivid red. There
are three pairs of these gills, which look like coarse feathers, just
behind the head.
The Proteus spends its whole life in total darkness, and at an almost
constant temperature of 50 F. The body is slender and decidedly
wormlike, but there are two pairs of very feeble, inconspicuous little
legs, placed quite far apart.
Nature has made the Proteus a true creature of darkness—perhaps more
so than any land-dwelling worm. As described by the late Dr. Austin H.
Clark, Smithsonian Institution biologist: “The Proteus is almost as
sensitive to light as a photographic plate. The light of a candle at
some distance is strong enough to make it restless. If it is kept in a
place from which light is not entirely excluded its white skin turns
cloudy with the appearance of gray patches, and if it is kept in an
ordinary lighted room it eventually turns jet-black.”
Proteus is eyeless. It seems feeble and helpless. Yet it is well
adapted for its life in dark caves. Most of the time it lies at the
bottoms of pools, completely motionless. But, says Dr. Clark, “any
small living thing in the water attracts its immediate attention. It
advances toward it, snaps it up and eats it. It seems to be guided
mostly by the movements of its victims in the water, possibly also by
a sense of smell. In the deep caves food naturally is scarce and the
animal often must go for a considerable time without anything to eat.
In captivity individuals have lived for months with no food at all.”
Ghostly dweller in the everlasting darkness of limestone caves in
the Ozarks is the Typhlotrition, a blind, wormlike white salamander
of the same general family as Proteus. It is a long, slender, nearly
transparent creature, which has evolved a long way towards complete
blindness. The newly hatched young have functioning eyes but these
degenerate in the adult so that it does not seem able to discriminate
light from darkness. It is barely able to stand on its thin, barely
visible legs. It lives on blind crustaceans and apparently spends most
of its life crawling through the small, underground streams which seep
through the limestone rocks of the Ozark foothills.
A quite similar creature of the same family was discovered in 1896 in
Texas during the boring of an artesian well. A subterranean stream
was struck at a depth of about 200 feet. From it this white, wormlike
creature was shot out, together with some remarkable crab-like
animals. A single specimen of a similar animal since has been found
in Georgia. Both these organisms are more wormlike even than Proteus.
They apparently have lived for milleniums in streams flowing hundreds
of feet below the earth. Both, it has been conjectured, are larval
forms of a well-known salamander of surface waters, which have become
permanent larvae. They have lost the ability to undergo metamorphosis,
like the change of a tadpole into a frog or a caterpillar into a
butterfly.
Most numerous of American limestone cavern animals are white, blind
grasshoppers—the cave crickets. They are small insects with antennae
about an inch long. With these they feel their way over the dank walls
upon which they swarm. Best known are three species of cave fish,
minnow-like and from two to three inches long. They have not lost their
eyes entirely, although these long since have been sightless. They
have compensated for the loss of sight by an extremely acute sense
of touch. The slightest movement of the water will send a school of
them scurrying for shelter among the rocks. The blind white worms are
supposedly their chief food.
None of the cave animals are very aggressive. Their chief nutriment
is believed to be organic matter carried by water, which seeps into
the dank chambers from the world above, but how they make use of this
is unknown. All are quite primitive types which have remained very
conservative after their first migration from the world of light into
the world of darkness. They are old both racially and in their behavior
as individuals. Secure in the black depths, some of them are quite
likely to be the last living creatures on earth.
_The Remarkable Clam Worms_
Fantastic giant of the nemertinean race is Cerebratulus lactus,
commonly known as “the clam worm” along the Atlantic Coast from Florida
to Massachusetts. It is from ten to twelve feet long, can contract to
two feet, and is an inch wide. Its favorite dwelling is a burrow six
to eight inches below the surface, usually in an old mussel bed among
broken shells and stones where it is almost impossible to sink a clam
hoe.
Outside the burrows it is seldom seen except occasionally at high tide,
gliding among sea weeds or in the shade of rocks in tidal pools. It is
unlikely that any burrow is occupied very long, as the nemertinea is
moving about constantly through mud in search of food. The animal is
highly specialized for burrowing. Ordinarily its “head”, or front end,
is broad and rounded. By a muscular contraction, however the shape of
the head can be made pointed and is thrust forward in the mud, when its
normal contour is resumed. Then again comes the muscular contraction,
the pointed head, and another thrust forward. This occurs over and over
again. The contraction waves follow each other so quickly that the
drilling process appears constant. The proboscis does not seem to be
used in the actual drilling operation, but is kept probing for points
of least resistance and turns aside at the slightest obstacle.
The favorite food of cerebratulus lactus is said to be another abundant
burrowing worm, the nereid, which is nearly as large in diameter,
belongs to a higher order, and has powerful biting jaws. The victim
always is swallowed tail first. Its burrow is a U-shaped tube in which
it is unable to turn around. The nemertean probes through the mud
for the tail end in such a burrow. The nereid, seized from behind,
cannot bring its fighting apparatus into use. Actually, however, it
never appears to struggle against being swallowed—a remarkable fact
since nereids fight fiercely among themselves. The reason, it has been
postulated, is that the victim’s nervous system is paralyzed by the
poisonous slime excreted by cerebratulus. When a minute drop of this
is placed on the tongue, it parches the whole mouth and the intensely
bitter taste remains a long time. The worm requires about ten minutes
to swallow a nereid, but by that time the prey is half-digested. The
flow of this mucous is quite copious. When several healthy worms are
placed in a pail, the bottom is soon filled with a hardening mass of it
from which the animals must be cut or pulled. When crawling, the worm
exudes a mucous trail, like a snail.
A comparable Mediterranean species, Nemertes borlasi, was described by
the French naturalist Quatrefages:
“This gigantic worm is from thirty to forty feet long, brown or violet,
and shining as varnished leather. It lurks under stones and in hollows
of rocks where it may be met with, rolled into a ball and coiled in a
thousand seemingly inextricable knots which it is incessantly loosening
and tightening by contraction of its muscles. The animal is nourished
by sucking a kind of small oyster which attaches itself to various
substances under water. When it has exhausted the food around, it
extends its long, dark-colored, riband-like body, which is terminated
by a head bearing some likeness to the head of a serpent. It pauses
gently, moves from side to side as if endeavoring to investigate the
ground, and finally succeeds in finding a stone to suit its purposes
about fifteen to twenty feet from its former retreat. It then begins to
unwind its coil and arrange itself in a new domicile. In proportion as
one knot is loosened, another forms at the opposite extremity.”
A report of the Gatty Marine Laboratory of St. Andrews University
in Scotland tells of the species Cerebratulus angulatus, which was
mistaken for a fish. “But when the fisherman stretched out his hand
net to capture it, instantly to his astonishment it shot out to more
than a yard long. In the laboratory it swam with undulatory up-and-down
movements, as an eel swims laterally.”
The nemertinea are a progressive race. Some have invaded the deep sea
and some the dry land. They have been obtained from depths of more than
6,000 feet. The deep-sea species have undergone peculiar adaptations
for a life of swimming slowly or floating idly at whatever depths
they have chosen for their habitat. They have lost their eyes and
their brains are quite rudimentary compared with those of their land
or shallow-water relatives. All have increased greatly the amount of
gelatinous tissue between the internal organs, so that they have a low
specific gravity. The deep-sea forms thus far collected are broad and
flat. Some have taken on the appearance of small fish with outgrowths
on the sides of the body which resemble fins, and with the rear end
flattened like a fish’s tail. Some have developed tentacles around
their mouths.
Most of the ribbon worms of the open sea are nearly transparent. Some,
however, are among the most brilliantly colored of the nemertinea race,
with coat patterns of yellow, orange, red, and scarlet. Most of these
creatures are small, measuring only a fraction of an inch in length.
The largest is about six inches long—thus, as one biologist points out,
comparing to the smallest like an ox to a mouse. These pelagic species
are found in all the oceans. They are carried around the world by
deep-sea currents.
About twelve species have abandoned the shore for dry land where they
lead active lives and seem to have become almost independent of water.
They cannot, however, endure being completely dried out. They do not
make their own burrows, but in periods of drought, it is believed, they
make use of earthworm burrows. Some have been found under the dead,
damp bark of tropical trees. Their chief food consists of earthworms.
_Winged Reptile_
The largest flying animal the world has known was a winged reptile,
the pterodactyl, of a hundred million years ago. It had a wing spread
of more than twenty feet, supporting in the air a body which would
hardly have weighed more than thirty pounds. Its head was nearly four
feet long with a dagger-like, narrow, pointed toothless beak. It lived
around the ancient sea which once extended northwestward from the
present Gulf of Mexico through most of Kansas. Presumably it lived
entirely on fish and made long, gliding flights over the water.
The structure of this reptile, insofar as it could be realized from
fragmentary fossil bones, was studied carefully by Dr. Samuel P.
Langley while he was at work on early models of his airplane. Did the
pterodactyl, Dr. Langley asked in a somewhat pessimistic progress
report, represent the best Nature could do in the way of flight? Could
man hope to do better than Nature?
_Vicious Fire Ants_
One of the most vicious of insects is the fire ant of South America—a
small red ant whose sting burns like the point of a red hot pin pushed
into the skin. Hordes of these creatures have forced the populace
to abandon Brazilian towns. The soil of a village can be completely
undermined by the ants. The ground is thoroughly perforated by the
entrances to their subterranean galleries.
“The houses are overrun by them,” says Edward Bates in _A Naturalist on
the Amazon_. “They dispute every fragment of food with the inhabitants
and destroy clothing for the sake of the starch. All eatables must
be suspended from rafters in baskets, with the cords well soaked in
balsam, the only known means of preventing the ants from climbing. They
seem to attack persons out of sheer malice. If we stood for a few hours
in the street, even at a distance from their nests, we were sure to be
overrun and severely punished. The moment an ant touched the flesh he
secured himself with his jaws, doubled his tail, and stung with all his
might.”
_The Architectural Genius of Birds_
Birds rival ants and termites as architects. One species builds nests
as big as small human dwellings—as much as 25 feet long, 15 feet wide
and ten feet high. This is the sociable weaver bird of the desert
western areas of South Africa. Such an apartment house, woven out of
sticks and straw, may contain as many as 95 individual nests. It is the
community product of a flock of from 75 to 100 pairs. The sheer bulk
of the nesting material gathered is striking evidence of the impelling
year-round urge of the building instinct.