the continuing individual. Inside the box is a little tentacled worm,
the polypide. It contains all the vital organs—the brain and the
nerve, circulatory and digestive systems. It breathes, hunts, eats
and lives quite independently of the zooecium. This polypide usually
is short-lived. It has no excretory system. Poisons pile up. It
degenerates and dies. When it expires the cells of the zooecium wall
assert themselves. From the dead cells of the polypide they extract
what nutritive material is present. The “inside animal” becomes a brown
speck-like body. Then the zooecium cells sprout a bud which becomes a
new polypide. This lives its normal life span and suffers the same fate
as its predecessor. Another brown body is the only evidence that it has
lived. This process may be repeated ten or twelve times. Think of a
man, or any other high animal, which could replace over and over again
its entire internal system with another made out of its own skin which
had eaten its own defunct brain and heart.
The relation of zooecium and polypide as it exists in one type of
bryozoa, the so-called “sea mats”, was vividly described by the great
British naturalist P. H. Gosse. These are not lace weavers. They form a
colony which looks like a pale, yellow leaf, such as Gosse found in a
microscopic study of a mass of sea weed in which he saw other animals
like “exquisitely crimson leaves thinner than the thinnest tissue
paper, with tall and elegant dark red feathers and purple filaments
each as fine as a silk worm’s thread.”
“Each individual cell [zooecium] of the sea mat”, Gosse tell us, “is
shaped like a child’s cradle. Suppose a coverlet of transparent skin
were stretched over each cradle, leaving an opening just over the
pillow. Suppose in every cradle there lies a baby with its little knees
bent up to the chin in that zig-zag fashion in which children often lie.
“But—the child is moving. A slowly pushed open semi-circular slit of
the coverlet and we see him gradually protruding his head and shoulders
in an erect position, straightening his knees at the same time. He is
raised half out of bed. His head bursts open and becomes a bell of
tentacles. This baby is the tenant polypide.
“The chambers themselves show signs of life. Their front doors
suddenly open, gape widely and shut with a snap. This opening and
shutting is repeated over and over again. The polypide emerges from the
cell slowly and withdraws like lightning at the slightest alarm.”
As mentioned before, some bryozoans appear to consist of three animals
in one. The third is the so-called avicularium, or bird’s head, also
vividly described by Gosse: “The cells [of this particular species]
are oblong-shaped, and look much like a sack of corn. Just below one
of the spines that crown the summit of the cell on one of the edges
is situated a small lump which bears a remarkable resemblance to the
head of a bird. It has a strongly hooked beak with two well-formed
mandibles, one of which is removable. You observe it deliberately
opening, like the beak of a bird and then closing with a strong,
sudden snap. The birds' heads are not inhabitants of the cells. They
are not even integral parts of them. The cells have their own proper
inhabitants, each leading its own life and each essentially formed on
the same plan as that of the baby in the cradle. There is no visible
connection between its and the bird’s head, which is cut off entirely
from the interior of the cell. This head has a muscular system entirely
its own. It seizes small animals but has no means of passing them into
its mouth”.
The real function of these avicularia is unknown. They have been
pictured as fierce watchdogs kept by the bryozoa for defense against
approaching enemies. Gosse speculates that they may serve indirectly as
hunters, seizing and killing small animals. The disintegrating bodies
of their prey, attract hordes of smaller sea creatures which can be
gathered up by the tentacles of the polypide.
_The Ways of Crabs_
Crabs that wear clothes, others that carry arms, and still others
that march like regiments of soldiers are among the curiosities of
Australia’s Great Barrier coral reef.
One crab forces the coral polyp to build a limestone palace for its
abode. The female of this species lodges on the polyp when it is in the
larval state and causes an irritation which forces the host animal to
build up the walls. The resulting house is just big enough for the crab
to move about in comfortably. There always is a door through which she
obtains her food.
Another species merely sits on the end of a sprouting coral which,
growing outward, makes a long, circular burrow for the crustacean.
Through this it can move backwards and forwards at will. The forward
part of its body is enclosed in a hard shell the exact color of the
coral so that when the crab sits at the door of its burrow it cannot
be distinguished from the coral.
Still another crab carries two sea anemones, one in each “hand”,
wherever it goes. In its first few months of life it seizes these
plant-flowers—living animals with stalks and petals like flowers which
ordinarily are attached to rocks under the water—about the centers
of the stalks. Thenceforth it moves about like a person carrying two
umbrellas.
The most logical explanation of this behavior is that the anemones
serve as weapons, killing or paralyzing small sea animals which come
in contact with them. This species of anemone has stinging cells in
its disk. These curious weapons are carried by the crab continuously
and seem essential to its life. When one of them is taken away, the
crustacean moves automatically to grasp it again. When a crab is killed
slowly in alcohol it clings to its weapons even in its death struggles.
There are spider crabs which cut and wear clothes. They cut off pieces
of living sponges and place them on their backs. These sponges become
entangled in tiny hairs which protrude through the animal’s shell, and
continue to grow until they protrude several inches over the back. Thin
layers also cover the under part of the body and the legs. Every time
a crab sheds its shell, it must make itself a new suit The practice
probably is beneficial to both animals. The crab, living in a forest
of sponges, looks like a sponge itself and is thus concealed from its
enemies. The sponge benefits by being carried to new food sources.
When the shell is shed the sponge simply attaches itself to a rock and
continues to grow.
One of the most remarkable cases of commensalism in nature has been
found by Dr. Melbourne Ward, Australian zoologist in a degenerate type
of barnacle which makes its way through the thin shell of one of the
Barrier Reef crabs. It wanders through the blood stream of the crab and
finally comes to the surface where it forms a little sac for itself.
Here it metamorphoses into another form and sends long, thread-like
filaments into every part of its host’s body. In some respects it
is like a cancer among higher animals, except that in this case the
malignant growth is that of an individual animal of another species.
It lives off the food eaten by the crab but never kills nor apparently
seriously injures its host. The one notable effect, for which there is
no adequate explanation, is that it changes a male crab into a female.
The soldier crabs are beachdwellers, about two inches long. They march
across the hard sand in perfect order, as if they were under the
control of leaders. No “officers”, however, have been observed. When
approached, they burrow rapidly in waves, like a regiment of infantry.
First the front rank disappears in the sand, followed in order by those
behind. The regiment disappears completely in a very short time.
The soldier crabs can hardly be driven into the water. When Dr. Ward
succeeded in pushing a few of them off the shore they were set upon by
ferocious small fish which rapidly devoured them. Realization of this
danger apparently is instinctive in the animals.
Some of the land-dwelling crabs of the mud flats dig very intricate
burrows with labyrinthine cross and side galleries. Some species live
in a communal life. Each crab has its own burrow, but from each there
is a passage into a large central hall which seems to be a community
gathering place. Other species are intensely individualistic. Each
excavates an elaborate labyrinth in the mud, considers this its own
home, and vigorously defends it.
During courtship some of these mud crabs perform dances like the
courtship dances of birds. The male of one variety, after attracting
a mate by his dancing, picks her up bodily in one of his nippers and
carries her away. Another variety of sand crab seems to have perfected
an engineering technique which still evades human skill—that of
building a burrow in soft, dry sand. These burrows are about two inches
in diameter. The crab is able in some mysterious fashion to compress
the soft sand into a solid substance with its nippers.
In precision of instinctive behavior, Dr. Ward found, these Great
Barrier crabs come quite close to the spiders, their distant relatives.
_Ticks With Noses in Their Legs_
Ticks, remote spider relatives, smell with their front legs. When these
legs are amputated the tick shows no reaction to odors. It cannot smell
blood but will feed on any sort of liquid sucked through a warm, moist
membrane like the skin. Presumably such a tick in nature recognizes
an animal as a proper source of food by smell, while a combination of
warmth and moisture from the skin gives a stimulus for feeding.
_The Fourth Realm of Life_
There is a wind-tossed green-grey ocean between earth and sky. It is a
sea on stilts, the world’s fourth realm of life. There are plants and
animals of the land, of the water, and of the air—and there are plants
and animals of the canopy of the rain forest, a thousand-mile-wide
broken belt around the world. It covers several million square
miles—the jungles of South America extending northward into southern
Mexico, the basins of the Niger and the Congo, strips of southern India
and Ceylon, much of New Guinea. Life is rather sparse in the perpetual,
drenched twilight of the jungle floor. It is abundant in the treetops,
the habitat of fantastic, and still largely unknown, plants, mammals,
birds, snakes, toads, frogs and insects. These might be compared to the
flora and fauna of an as yet unexplored continent.
Rain forest trees are, in general, tall, straight, and branchless until
near their tops, 100 to 150 feet above the ground. There they send out
a rich profusion of branches and foliage. This foliage is like a thick,
rough, continuous green blanket held up by tall posts, like a net below
trapeze performers in a circus tent. The top of the blanket is a place
of intense sunshine. Light grows dimmer and dimmer as it penetrates the
leaves and the branches. Finally, on the jungle floor, there is only
about a fiftieth as much illumination as on the surface of the canopy.
In the canopy four or five kinds of monkeys take the place of man on
earth as the most intelligent and adaptive animals. Primates from
the beginnings of the race—the weird, squirrel-like animals of the
North American dawn age forests fifty million years ago—have been
semi-arboreal.
Most abundant in the tree-land are the pretty, playful,
curiosity-driven, humanlike spider monkeys who play tag and throw
sticks at each other in the lower branches. Best known, although less
likely to be seen, are the big, black, Satanic-looking howlers.
Both of these species, in the long process of adapting themselves to
high jungle life, have made third hands out of the ends of their tails.
With these highly sensitive prehensile organs they not only clutch
branches but sometimes carry out rather delicate manipulations.
Weirdest are the black-and-white striped, woolly-furred night monkeys.
These little racoon-like creatures live in holes far up in the
treetops. They come out only at night and are seldom seen. They have
enormous eyes which shine like live coals among the leaves when the
light of a flash lamp catches them.
Probably the most dangerous single animal of the canopy is the
tamandua, or golden anteater. It is exclusively a treetop creature,
about the size of a rabbit, with golden-yellow, soft, silky fur. It
lives almost exclusively on termites which it harvests by sticking
its long tongue, covered with a sticky saliva, into their nests. A
progressive relative of the sloth, it remains motionless apparently for
days at a time and is a slow, clumsy climber.
But woe to anything—jaguar, ocelot, big howler monkey, even man—that
runs afoul of it. It strikes suddenly and fast with its long, curved
scimitar-sharp claws, and always aims at the stomach which it rips
open. No other creature will venture near a tamandua, except by
accident. Probably it is voiceless, although natives have attributed
to the sinister little anteater a peculiarly weird cry heard in the
moonlit jungle. This now is believed to be the call of a bird.
Climbing rats are abundant in the jungle top. They feed, for the most
part, on fruits. Here also is the abode of pigmy squirrels which cling,
heads downward, to the tree trunks with their tails curled over their
backs, squirrel fashion. These animals are about five inches long,
including the tail whose length is about equal to that of the rest of
the body. There is a tiny, climbing mouse with short, broad feet and
sharp, curved claws. Bats, mostly small, fruit-eating animals, flutter
about in the darkness. Probably there are few of the big dangerous
vampires in the high treetops. They fare better on the blood of larger,
ground-dwelling creatures such as tapir and peccary.
_Rubber-Band Worms that Stretch and Stretch_
There is a worm ninety feet long. It is the giant of a family of white,
red, yellow, green, purple, and violet worms whose habitat ranges from
sea bottoms to jungle treetops. The worms shoot poison-tipped harpoons
out of their brains. Most can shrink at will to less than a third of
their ordinary length. They always shrink when they die. Some can break
up into hundreds of fragments, each of which will grow into a complete
new worm. They tie themselves into inextricable knots. They build their
houses from the slime of their own bodies.
This class is that of the ribbon worms or nemertina. There are about
five hundred known species—perhaps as many more are unknown. Still
near the bottom of animal life, they represent revolutionary advances
from the lowest of worms, the planarians, with which they share many
characteristics. They have evolved integrated brains and nervous
systems. They have, for the most part, taken on a true worm shape.
They have acquired weapons and, in some cases, arsenals of weapons.
They have eyes that see. They have a digestive system, a mouth near
the front of the body, and closed blood system through which flows a
liquid which usually is colorless as water. Perhaps they hear. At the
top of the head in certain species there is a group of cells with hairs
and bristles which may constitute an organ of taste. Along the way of
achieving these advances they have given up a little freedom and a
little immortality for a little more efficiency.
Those best-known are inhabitants of sea shores, especially the
Atlantic coasts of North America and Europe. They live under rocks, in
abandoned mollusk shells, in windrowed masses of sea weed, in thin,
parchment-like tubes which they secrete from their own skin. Their
general appearance is that of a tangled mass of slimy string, but some
members of the family have among the most brilliant color patterns
known in nature.
The most conspicuous organ of these primitive worms is the proboscis,
a hollow string which is shot out with great speed and force from the
front end of the usually cylindrical body. At the end of the string, in
several groups, is a sharp-pointed, barbed spear-like stylet with which
the prey, usually some minute water animal, is speared. The victim then
is drawn back into the mouth by the attached hollow thread. Some groups
have no stylets. The thread, upon which is a mucilage-like mucous, is
used like a lassoo and coiled tightly around the prey.
The proboscis is associated so closely with the brain that, like the
retina of the eye, it has sometimes been considered an extension of
it. The thread often is as long as the worm itself. It is shot out
with such force that is frequently breaks off and continues to lead an
independent life for a few hours. A new proboscis always develops.
When coiled, the proboscis rests in the center of the two-lobed brain.
It is continuously shot out and pulled in and probes the water around
it. Presumably at first it was an extremely sensitive sensory organ
by which the brain was kept aware of its surroundings. The attached
stylet, an offensive weapon, was a later development.
In a few cases the thread carries a multitude of unattached barbed
points, a sort of machine-gun arrangement, which can be hurled in all
directions in the hope of hitting something. It also carries tiny hooks
by which it can be attached to some object. By means of the attached
line the worm pulls itself forward over beach or sea bottom, its
ordinary means of locomotion. It is also able, however, to glide like a
planarian and to swim.
Nemertinea breath through the walls of the oesophagus, or gullet.
When the tide comes in, shore-dwelling species rapidly swallow and
eject mouthfuls of salt water. Oxygen to purify the blood is obtained
from the water. The blood circulates in two or three vessels. It is a
colorless plasma in which float both green and red corpuscles.
There is little knowledge as to the precise nature of the nemertinean
sensory organs. There are, however, nerve cells in all parts of the
body and the animal is quick to respond to any irritation, especially
to any chemical change in the water. With an intense stimulus the body
is contracted violently, twisted, and even torn apart. Even a headless
specimen will move toward food placed nearby. A severed head may
continue to creep restlessly for several hours. The headless body moves
only when stimulated. With most mud-dwelling species it is difficult to
secure an entire specimen. The slender, fragile body is likely to break
into many fragments when disturbed. Quite commonly, even without any
particular disturbance, a large worm will break up into a dozen or more
pieces. Each becomes a small, new animal. Some regenerating fragments
secrete disks of mucous and form cradles, in which they may remain for
months while new organs are being formed. Eventually the disk ruptures
and the new worm emerges. There is a specific tendency in some species
thus to reproduce during warm weather, with a brief period of sexual
reproduction during the cold months.
These worms are extremely tenacious of life. Even without food they
may live as long as a year in the proper environment. Ordinarily
they are quite voracious animals. They eat earthworms, other sea
worms, small mollusks—almost anything soft-bodied which the eternally
active proboscis can bring to the mouth. There it is sucked into the
digestive tract. The digestive process is very rapid. Some species
have distensible mouths. Like snakes, they can devour animals bigger
than themselves. Some are cannibals. When times are hard they can,
like planarians, absorb themselves. A case has been known where a
nemertean digested all but a twentieth of its own body in a few months,
apparently without any ill effects. The lost tissues were restored as
soon as food again was available.
_Frog Versatility_
Animals of many talents are the frogs. Some grunt like pigs, others
cackle like hens. Some chirp like crickets, others caw like crows.
Still others quack like ducks. There are golden frogs, scarlet frogs
that play dead, frogs that build houses.
All this assembly is found in one small corner of the world,
southeastern Brazil. This particular tropical countryside long has been
known for the abundance and variety of its amphibian life.
Some of the frogs in this area are particularly notable for their
coloring. Two are almost solid gold in color. Perhaps the most notable
is Brachycephalus ephippium, which not only is brilliant gold in hue
but has armor plates of bone on back and head, and whose tadpoles are
nearly three times the size of the adults. All the adults, less than an
inch long, have the armor plate strongly developed, although the shape
and size shows considerable variation. The general form of the bony
deposition just under the skin, in no way connected with the skeleton,
appears to be typically that of an hour glass across the back with one
or more separate bony islands. Sometimes these islands are fused with
the hour glass. The adults hide under leaves and fallen tree trunks in
high mountain woodlands and come out in large numbers only in rainy
weather. They appear to be rather clumsy creatures. Their gait is a
slow walk.
The nightly chorus of certain of the frogs sounds like a regiment
beating on tin pans. Others have calls that are like the sounds made
by winding a watch or filing iron. The “tin-pan frog” is one of the
most conspicuous creatures of the region. The chorus of singing males
gives a booming metallic sound which seems at times to be a regular
clanging, like that of a blacksmith hammering on an anvil.
The “tin-pan” frog builds its own house—a crater-like structure of mud
projecting above shallow water within which its eggs are laid during
the dry season. These nests usually are constructed close to the
water’s edge. Here the eggs hatch and the young tadpoles are swept into
the pond by the next heavy rain. The mud walls apparently protect the
eggs from depredations by fish. Adults stay in trees except at the time
of egg-laying. The male is said to come to the pond first to build the
nest, before the female arrives to lay the eggs. The frog that quacks
like a duck is a closely related species. It has a peculiar habit of
swarming. Hundreds may appear at one time in a single tree.
One of the golden frogs is about three inches long and almost pure
gold in color. Its voice is like the slow grunting of a pig. It sleeps
during the day in large leaves of bromeliads, trees of the pineapple
family that often hold rainwater in their axils. They sometimes are
described as living “tubs of water.” At night the frogs come down out
of the leaves and go to ponds and streams in the neighborhood in search
of insects. Their leaf sleeping chambers apparently give them complete
protection from their natural enemies.
One gray and brown Brazilian frog, extremely sluggish by day, when
handled assumes a wooden, dead appearance, with the limbs brought close
to the body and the head bent forward, so that it resembles a patch of
fungus or a chip of wood. Even when left on their backs for a long time
they continue to play dead.
A notable singer among the Brazilian tree frogs is Hylabypunctata,
whose call is a high, frequently repeated tit-tit-tit. When many sing
together the chorus is so loud it can be heard nearly a mile away.
One brilliant-red-legged frog, brought to Washington by the Smithsonian
Institution, ate nothing for seven months and did not change its
position for days at a time. Throughout this period it seemed to lose
no weight. At the end of seven months it eagerly ate worms and files.
A violet frog that lives in the clouds and sings like a bird has been
discovered by Dr. Bertha Lutz of the National Museum of Brazil on the
summit of 10,000-foot-high Mt. Itatiaia in the Mantiquiera mountains.
This frog, hitherto unknown to science, has a purple back spotted with
gold, bronze and deep yellow. Below the purple is a deep violet blue.
Since the Mantiquiera mountains, the highest in Brazil, are almost
perpetually cloud-veiled, the little animal appears to be entirely a
creature of cloudland. Its curious colors perhaps have been borrowed
as camouflage from the sky. It has a weak voice and its song is very
much like that of a bird. It is found in swift mountain brooks, part of
whose courses are subterranean.
_The Horned Viper Spears Other Animals_
Best-known Egyptian cobra is the so-called “spitting serpent” or Libyan
asp. It supposedly has the ability to spit in the eyes of its enemies,
such as dogs, and the saliva temporarily blinds the victims.
The cobra was a sacred animal in ancient Egypt. It was associated with
the sun and with royalty. It formed part of the head dress of solar
deities and was represented in the crowns of kings and queens. Toward
the end of the 20th dynasty, when it became the custom to preserve
sacred animals, it was embalmed at Thebes.