Part 15

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.