as an expression of nature’s artistry—in Cuban forests. Delicate
sunrise tints of pink, blue, violet, green and yellow make the shells
of two or three genera of tree-dwelling mollusks like rare jewels. Most
conspicuous are snails of the genus Polymita, confined to the Oriente
province. Here they cover some trees so completely that the effect is
like that of a tree of flowers. Only upon close observation can one
detect that the blossoms are shells.
The animals live for the most part on a fungus that grows on the
bark. The colors of the shells are affected by various chemical
constituents of the bark, notably tannic acid, and serve as warning
to other creatures. In taste the snails are very bitter and no bird
will intentionally attack them. The color serves notice that only a
disgusting mouthful is to be had.
Two of the most beautiful of these shell forms were recently discovered
by Dr. Paul Bartsch, former Smithsonian curator of mollusks. Fragile,
translucent, colored as delicately as the loveliest of orchids,
these particular snails are the fairies of the mollusk world in the
unconscious artistry with which they have constructed their moving
palaces. One, a hitherto unknown species, has a remarkable combination
of pale orange, orange buff, deeper orange and flame color—all shading
delicately into each other. The color effect is such as one might find
rarely in rose petals. Another has a blending of ivory, olive green,
lemon yellow and orange.
_Termites That Eat Lead_
On Barro Colorado island in the Panama Canal Zone the Smithsonian
Institution maintains an “experimental cemetery.” It consists of rows
of upright posts which look like gravestones, half buried in the soil.
The purpose is to test the propensities of the island’s 42 species of
termites—just about man’s most persistent and expensive enemy in the
tropics—to eat different kinds of wood impregnated with different kinds
of repellants and poisons. To date approximately 35,000 tests have
been made. The longer the work is continued the more Dr. James Zetek,
former director of the station, is impressed with the contrariness and
ingenuity of the blind, ant-like insects which achieve sub-human acmes
of engineering ability, and whose appetites are marvelous.
Among Barro Colorado’s termites are some extraordinary bugs indeed.
One, for example, eats lead. It gnaws its way through the lead
sheathings on cables. This is not because it likes a lead diet. Lead,
in fact, is indigestible and the insects starve to death. But their
appetites are so insatiable that the little creatures just keep on
gnawing, in the hope that there will be wood on the other side.
This particular insect is known by the scientific name of coptotermes
niger. It has been known to eat through a concrete floor nearly five
inches thick—again not because of any particular liking for concrete
but because of the expectation of coming eventually to digestible
wood. The feat was made possible because the sand used in making the
concrete contained many fragments of sea shells which were dissolved by
a powerful chemical excreted by the insects.
It is very difficult to dispose of termites by poison—that is,
permanently. Races have risen here, for example, which seem to thrive
on arsenic. The insect lives on the cellulose in wood. This must be
digested by certain intestinal bacteria in the digestive tract. If
these microörganisms can be poisoned the termite starves. At first at
least 99 percent of the bacteria succumb to heavy doses of arsenic.
This means that 99 percent of the termites are killed. But always there
are a few exceptionally tough bacteria with a high resistance to the
poison. Their descendants in a few generations apparently become almost
entirely resistant. With their help a new race of termites comes into
existence.
Ordinarily termites attack only dead or dying wood. Some of them,
however, carry fungi around with them to kill their own wood. The
Canal Zone insects can dispose of living trees. Dr. Zetek tells of one
attempt to establish an avocado plantation. He warned against it. When
the trees had reached the fruit-bearing stage and seemed healthy he
was ridiculed for his warnings. Branches were heavy with avocados and
there was promise of a record crop. He shook his head when shown the
flourishing orchard. “The poor trees,” he remarked. “They know they are
going to die. They are just making one last mighty effort to preserve
their species by producing plenty of fruit and seeds.” He secured the
orchard owner’s permission to chop down one tree. The whole inside, he
found, was riddled with termite galleries. This tree and all the others
in the orchard were dead within a year.
_The Plant That Eats Animals_
There are life-and-death battles in the microscopic world between
tiny shelled animals and flesh-devouring fungi. The phenomenon can be
compared to that of a tree catching and eating big turtles.
When a culture of diseased plant roots is made, there soon appear great
numbers of microscopic plants and animals—bacteria, fungi, amoebae,
nematodes and other life forms. Immediately the struggle for survival
starts. The animals try to eat the plants and the plants attempt to
devour the animals.
Among the animal forms which appear are vast numbers of creatures
known as rhizopods. Practically unknown except to specialists, these
microscopic creatures play an important part in the economy of life.
They are probably the best-equipped of all the new arrivals to survive,
since their soft bodies are covered with relatively heavy shells.
Some years ago Dr. Charles Dreschler of the U.S. Department of
Agriculture reported the existence of predaceous meat-eating
fungi—parasitic forms of plant life—which literally lassoed such
unprotected animals as amoebae and thread-like nematodes and proceeded
to devour them at leisure by the process of infiltrating their bodies.
It would appear that the armored rhizopods are completely protected
from these ferocious plants.
But the animal has one weak spot in its defense. It must get its mouth
outside its shell in order to eat. Apparently the most inviting forage
at hand is the innocent-appearing fungus. The rhizopod proceeds to
suck at it with movements which Dr. Dreschler describes as similar to
“sucking an egg.”
The rhizopod mouth is small. Once it has sucked in any of the
fungus its fate is sealed, for, explains Dr. Dreschler, “to such
undiscriminating voracity the fungus responds by rapidly proliferating
from the partly ingested portion a bulbous outgrowth slightly larger
than the mouth, so that the rhizopod is held securely.”
The unfortunate shelled animal is like a fish caught on a hook. It
struggles vainly to get away. It rushes, but the fungus simply lets
out the line until the rhizopod is brought to an abrupt stop and can
be hauled in. The line is a filament connecting the body of the fungus
with the bulb in the animal’s mouth.
Once its prey is secure, the fungus proceeds to send out growths from
the bulb through the creature’s flesh, literally eating it alive. Very
rarely, like a hooked fish, a rhizopod is able to break away.
In the course of its life, a single one of these thread-like fungi
will capture many of the shelled animals, lining them up securely
mouth-to-mouth on both sides of itself. It absorbs their substance at
its leisure. Other predaceous fungi have definite external organs for
capturing their prey. This particular species, however, has no external
appendages and appears completely inert and innocent until it is
stimulated to action by the sucking of the rhizopod.
_The Ocean’s Sound Barrier_
A densely woven carpet of life covers the floor of the world of light
under the sea—just below the level reached by the most penetrating rays
of the sun. It is a carpet of many colors and of flashing lights, the
strands of its texture rapidly moving, predaceous, warring organisms.
They probably are a mixture of lantern-carrying fish, ten-tentacled
squid with malevolent red eyes, and small, luminous, shrimp-like
creatures known as euphasids. Their nature can only be deduced by the
echoes of sound from their bodies.
This carpet, about 300 feet thick, is the sea’s “false bottom.” It was
discovered by Navy ships making depth soundings during the war. Such
soundings depend on the time taken for echoes to be reflected to the
surface from the ocean floor. Recorded on a ship’s instruments, they
represent an extremely precise procedure perfected to the point where
a continuous record of depth can be obtained with an accuracy of a few
inches.
But, using certain wavelengths of sound, echoes were received from
depths between 1,000 and 1,500 feet, whereas the sea itself was known
to be two or three miles deep at these places. The only plausible
explanation was that there were vast multitudes of floating or swimming
objects of some sort, constituting almost a solid surface, at the
depths from which the echoes came. The mystery was increased by the
fact that the false bottom existed only during daylight. The carpet was
laid shortly after sunrise and rolled up at twilight. The indication
was that the echo-producing objects rose to the surface at the
beginning of darkness—a clue which has given rise to much speculation
and argument.
The carpet is under all the oceans, even the nethermost Antarctic. In
some areas it seems practically continuous over thousands of square
miles. In others it is broken up into smaller areas, like scatter rugs
on a floor.
The false bottom is almost as much a mystery today as when it first
puzzled the Navy’s navigators. All are agreed that it must be composed
of vast hordes of animals. They are not directly observable by any
known technique. Some indication of their size and abundance, however,
can be deduced from the wave lengths of sound which they echo. There
must be, it has been calculated, from ten to twenty of these organisms
in each cubic meter of water. They echo only long sound waves. High
frequency sound passes through them like light through glass and is
bounced back from the true sea bottom. They have been a mild nuisance,
but never a peril, to modern navigators.
Whatever the organisms may be, they evidently cannot endure any light.
At dawn they sink immediately from within about 100 feet of the surface
through the zone of moonlight-pale, green illumination which represents
sunshine’s deepest penetration of sea water.
Chief proponents of the theory that a preponderance of them are squid
are oceanographers of the Navy’s Hydrographic Office. It is well
established that the deep sea abounds in these fantastic mollusks.
They rarely are seen at the surface. They move through the water very
rapidly by a kind of jet propulsion, gulping water in the mouth and
shooting it out explosively from the rear. They are little affected by
changes in hydrostatic pressure, as are fish with air bladders. When
the false bottom rises at sunset it comes to the surface at a rate
of forty to fifty feet a minute. No swimming fish, it is maintained,
could rise so rapidly through the decreasing pressure. It would get the
“bends”, like a human diver brought to the surface in too great a hurry.
These squid range in length from three or four inches to more than a
foot. They are of about the right size to return some of the echoes
which have been observed. The faintly luminous euphasid shrimps also
are known to be very abundant in the depths. Presumably they provide
most of the squids' food.
The principal investigations have been carried out by the Navy’s
Electronics Laboratory and the Scripps Institute of Oceanography of San
Diego. An outstanding difficulty hitherto has been that the echoes have
been known only from the false bottom as a whole. They have covered
a wide spectrum of sound wavelengths. A recently developed technique
is to lower a hydrophone connected with a sound-producing mechanism
into the depths in order to record echoes from individual objects at
distances of a few feet. Indications to date are that some of them are
from a foot to eighteen inches long—too large to be squid and far too
large to be shrimp. They can only, it is deduced, be deep water fish.
If a great number of fairly large fish are indicated, this false
bottom might turn out to be the richest pasture in the ocean for the
production of food for man.
Navy divers have swum through the false bottom at night when it was
within less than 200 feet of the surface. They have observed enormous
numbers of euphasids and other small organisms—but very few fish. This,
however, is only suggestive. There is no good reason to believe the
carpet has the same texture at night as by day. It is quite likely that
the organisms disperse widely over the surface waters.
_Snakes That Act and Look Like Worms_
There are snakes that look like snarls of six-inch-long pieces of
wrapping twine. These worm snakes are the world’s closest imitators
of worms. Among the most secretive of living things, they rarely come
in contact with man. When they are seen they usually are mistaken for
worms. Only zoologists can put them in their true families. These
living strings live exclusively under the earth, sometimes in tangled
snarls of scores of individuals.
They are the smallest of snakes. Their closest relatives, however, are
the gigantic boas and pythons. Judging from their wide distribution—on
such isolated spots, for example, as Christmas Island in the Indian
Ocean—they are quite ancient reptiles whose wanderings started about
fifty million years ago.
They are found most often in termite nests, where they eat the eggs
and possibly the larvae. Small earthworms and other soil creatures add
to their diet. The worm snakes are almost toothless. Eyes are buried
under skin, are only faint spots, and probably only can discriminate
light from darkness. The tail looks somewhat like the head—a likeness
presumably developed as a camouflage. They retain a snake’s scales, but
these are highly polished so they can be of no help in crawling.
These Typhlopidae and Glauconidae, as the two major groups are known,
are extremely active. When they are exhumed they start at once to
burrow back and have been found as much as two feet underground.
Occasionally they may be found in mole holes or in rotten wood where
they feed on insect larvae and also, it is likely, get some warmth
from the decay process. The snout is used in burrowing. They are hard
to hold in the hand, owing to the high polish of the scales. There are
approximately 100 species scattered over the world, two coming as far
north as the Texas border. They have teeth in only one jaw—the upper
jaw for Typhlopidae, the lower for Glauconidae.
_A Porcupine of the Sea_
Among the weirdest creatures of the deep is also one of the latest to
become known to science—the sea urchin (closely related to star fish)
astropyga magnifica. It is the largest sea urchin yet found in the
Atlantic. It has approximately 200 bright blue eyes arranged in double
rows. The body is covered with several hundred sharp, barbed black
spines nearly a foot long.
That so conspicuous an animal, living in such a densely populated
region—one of the most intensively studied in the world by
biologists—should have remained undiscovered so long probably is due to
two reasons. First, if its habits are at all comparable to those of its
nearest relatives, it is strictly nocturnal and comes out to forage on
the coral sands of the shallow sea bottom only after light has ceased
to penetrate the water. During the day the creatures remain secluded,
often congregated in great numbers, in holes and caves of the sea floor
and under the coral.
Second, it is quite similar in appearance to another smaller member
of the sea urchin race with spines as much as 18 inches long which
is greatly dreaded and is even reputed to have caused the death
of children who have fallen on it. Anybody coming upon a daytime
bed-chamber of these fantastic creatures would be likely to leave them
strictly alone.
This particular sea urchin is especially interesting in the development
of its eyes. These appear to be true sight organs. If a hand is placed
in the water near one of the animals the long barbs immediately are
pointed in the direction of the intrusion, and as the hand moves the
barbs move. Such a creature is practically impregnable. It never,
however, takes the offensive. It cannot “throw” its barbs, but they
enter the flesh easily and cause painful local irritation. Some species
inject a virulent poison which may even kill a human being. There is no
evidence that this species is toxic.
Astropyga magnifica, which has more the appearance of a porcupine than
of any other land animal, is a scavenger of the sea bottom. It gathers
and devours the accumulated debris that falls through the water. It
never kills its own food, so far as is known. It has five sharp teeth
in its mouth, located on its under surface, with which it can chew away
the flesh of dead animals.
This sea porcupine has a peculiar system of locomotion in common with
most of its relatives. It has literally thousands of sucker-like feet,
which are hollow and attached to tubes within its shell. It moves
by forcing water through the tubes and into the particular “feet”
which it wishes to use. When these are out of use they are contracted
by withdrawing the water. Being a radially symmetrical animal, the
creature can move with equal ease in any direction. It has no
head—that is, the development of its nervous system and the direction
of its locomotion are not fixed in a forward direction, as is the case
with vertebrates and insects.
Some members of the sea urchin family have hoof-like formations on the
ends of some of their spines, with which they are enabled to walk over
the sea bottom without using the suction disks. About the only enemy
of these fearsome nightmares of the deep is man. Some species are used
extensively for human food, notably among the Mediterranean coast and
in the West Indies. The developing eggs are taken from the body and
eaten either raw or cooked. Even if it should prove suitable for human
food, it is unlikely that the sea porcupine ever will be a rival in
this respect of its rival, the “sea rabbit.” It is too secluded in its
habitat.
_Worms That Are Unkillable_
In nematodes life may have reached its greatest capacity for survival.
The remarkable persistence of these soil worms has been studied by C.
W. McBeth, researcher of the Shell Oil Company. One form, he reports,
has been known to survive after 25 years in a glass bottle in a
laboratory. Another, a pest of wheat kernels, apparently came back to
life after 28 years in laboratory storage. A nematode which had invaded
a rye plant, collected in Kansas in 1906, revived after 39 years of
complete dehydration in a herbarium.
Those which live as active feeders in the soil, however, are not
particularly long-lived. Each species depends on a certain plant type
and must starve if this is not available. The recently introduced
golden nematode of potatoes, a particularly obnoxious pest, is known,
however, to survive as much as ten years in soils where no potatoes
are planted. A great mass of eggs is produced, but not laid. They are
retained in the body of the mother, who dies. Her skin remains—a bag
filled with eggs.
This stays in the soil, apparently unharmed by changing conditions,
until potatoes are planted again. Then some mysterious influence, as
yet unexplained, causes the eggs to hatch and the whole nematode cycle
begins once more.
Due to such a strange tenacity of life this nematode is about the
hardest of pests to control. It refuses to stay dead. Other species
likewise are specialized in one or more ways of survival under adverse
conditions.
Because of the complexity and minuteness of the nematodes, it has
been very difficult to determine the effects of heat, cold, flooding
and drying on different species. These vary for each. One nematode
species, especially resistant to drying, has a skin consisting of nine
layers. The ability of this skin to hold moisture inside the minute
body undoubtedly is an important defense mechanism. Some species
are entirely marine, others are parasites within the bodies of other
animals. It has been found that both of these varieties possess skins
which are much more permeable to moisture. The original home of the
phylum probably was in the sea, but a moisture-proof cuticle has been
developed by those which have invaded the land.
The whole body structure of the plant nematode is almost ideally suited
to life in the soil. The typical eel-shaped body is well-adapted for
moving in the moisture surrounding soil particles. Deviations from this
eel-form in certain stages of some species, usually in mature females,
are found only in sedentary stages. The larvae and males retain the
ancestral shapes. Another deviation is found in the so-called “ring
nematodes” which have short, plump bodies incapable of locomotion in
the typical whip-like fashion. Movement is accomplished by alternate
expansion and contraction of the body.
A majority of nematodes spend a greater part of their lives in the
soil. A few, however, are carried from plant to plant by insects.
Although moisture is necessary if the tiny animals are to remain
active, the soil seldom becomes too dry for them except in the top two
or three inches. Their structure is well-adapted for moving up and down.
_The Remarkable Brachiopods_
A part of the fantastic living world of 200,000,000 years ago has been
dissolved out of about thirty tons of yellowish-brown limestone by a
Smithsonian paleontologist.
The rock comes from a low mountain range in southwestern Texas—the
Glass Mountains, about 250 miles east of El Paso. During the Permean
geological period, when some of the earliest known forms of animal
life appeared on land, the site of the Glass Mountains was a muddy
bottom, probably close to the shore of a warm sea. A bewildering array
of animals lived in that sea. They died and eventually were buried in
the mud. In some cases their bodies were covered with silica. In others
silica replaced the shells. When these rocks are placed in hydrochloric
acid the limestone is eaten away but the silica shells remain. Years
of skilled labor would be required to chip out of the rock what is
obtained in a few days in the acid bath.
Most abundant animals of the ancient Texas sea were the brachiopods
or lampshells—essentially shelled worms. The broad road of life is
strewn with derelicts, stragglers and deserters. Among the most notable
among them are these obscure creatures which, in numbers and apparent
prosperity, seem to have been close to the dominant animals in the
world in the days when giant amphibians, remotely related to present
frogs and toads, and monster scorpions were establishing themselves on
dry land.
Brachiopods were among the first animals to leave any traces on earth a
half billion years ago. Even at that time they were complex creatures,
with nerves and stomachs, which indicate a long ancestry before they
left any fossil remains. In the tepid Permian seas they reached their
climax in numbers and variety. They survive today, but only in a few
places. For all practical purposes they are now among the most obscure
animals in existence. In the whole world there are about 110 extant
species compared to nearly 500 which Dr. G. Arthur Cooper, Smithsonian
Institution curator of invertebrate paleontology, and his associates
have obtained from one small area of the Glass Mountain limestones.
The existing brachiopod might be mistaken for a small clam.
Zoologically, it is an intermediate form between mollusks and annelid
worms, and somewhat closer to the latter than the former. Its way of
life actually is nearer to that of an oyster than to that of most
worms. It now is believed to be most closely related, through some
unknown common ancestor, to the bryozoa or lace weavers. In the past
both were classified together. The brachiopod never has become a
colonial animal.