Subterranean Vegetation—Fungi—Enormous Fungus in a Tunnel near Doncaster—Artificial Mushroom-beds near Paris—Subterranean Animals—The Guacharo—Wholesale Slaughter—Insects in the Cave of Adelsberg—The Leptodirus and the Blothrus—The Stalita tÆnaria—The Olm or Proteus—The Lake of Cirknitz—The Archduke Ferdinand and Charon—The Blind Rat and the Blind Fish of the Mammoth Cave.

Of all the phenomena which attract the naturalist’s attention, as he wanders over the surface of the earth, there is none which makes a deeper impression on his mind than the omnipresence of life. On the snow-clad cone of Chimborazo, 18,000 feet above the level of the sea, Humboldt found butterflies and other winged insects, while, high over his head, the condor was soaring in solitary majesty. At the still greater elevation of 18,460 feet, at the Doonkiah Pass in the Himalaya Mountains, Dr. Hooker plucked flowering plants, and saw large flocks of wild geese winging their flight above Kunchinjinga (22,750 feet) towards the unknown regions of Central Asia. Thus man meets with life as far as he is able to ascend, or as far as his sight plunges into the atmospheric ocean. Besides the objects visible to his eye, innumerable microscopical organisms pervade the realms of air. According to Ehrenberg’s brilliant discovery, the impalpably fine dust which, wafted by the Harmattan, often falls on ships when hundreds of miles from the coast of Africa, consists of agglomerations of silica-coated diatoms, individually so small as to be invisible to the naked eye; and everywhere numberless minute germs of future life—eggs of insects and sporules of cryptogamic plants—well fitted by cilia and feathery crowns for an aËrial journey, float up and down in the atmosphere; while the waters of ocean are found, in like manner, filled with myriads of animated atoms. But organic life not only occupies those parts of our globe which are accessible to solar light; it also dives profoundly into the subterranean world, wherever rain, or the melted snow, filtering through the porous earth, or through vents and crevices, is able to penetrate into natural caverns or artificial mines. For the combination of moisture, warmth, and air is able to develop organic life even thousands of feet below the surface of the earth; while light, though indispensable to most creatures, would blight and destroy the inhabitants of the subterranean vaults.

On surveying the flora of these dismal recesses, we find it consisting exclusively of mushrooms or fungi, the lowest forms of vegetation, which, shunning the light, love darkness and damp. Their appearance in the caves is, as everywhere else, dependent upon the existence of an organic basis, and thus they are most commonly found germinating on pieces of wood, particularly in a state of decomposition, which have been conveyed into the caverns either through the agency of man or by the influx of water. Species of a peculiarly luxuriant growth are sometimes seen to spread over the neighbouring stones, or apparently to spring from the rocky ground, where, however, on closer inspection, vestiges of decayed organic substances will generally be detected.

Thus vegetation in caves most commonly keeps pace with the quantity of mouldering wood which they contain, and flourishes not only near their entrance but in their deepest recesses, as, for instance, in the Cave of Adelsberg, where, at a distance of more than a thousand fathoms from its entrance, the pegs which have been driven into the stalactital walls for the purpose of measuring its length are covered with a rich coat of fungi. Nothing can be more curious than to see these plants, thriving and luxuriating in deep stillness and gloom, under circumstances so alien to the ordinary conditions of life. Among the fungi found in caves, many also vegetate upon the surface of the earth exposed to the influence of light, and not seldom degenerate into monstrous forms in their less congenial subterranean abodes; but many are the exclusive children of darkness. The Austrian naturalist Scopoli published in 1772 the first exact description of more than seventy subterranean fungi, collected chiefly in the mines of Schemnitz and Idria; and about twenty years later Humboldt wrote his celebrated treatise on the same subject.^[19] Since then G. F. Hoffmann has described the subterranean flora of the Harz Mountains;^[20] and latterly the botanists Welwitsch and Pokorny have examined the caves of Carinthia, where they discovered no less than eighteen species of fungi, among others the mouse-tail mushroom (Agaricus myurus, Hoffm.), which is also found in the Harz, and bears on a slender hairy stalk, more than a foot long, a small hat, scarcely a quarter of an inch in diameter. Some of these fungi are remarkable for their size (Thelephora rubiginosa sanguinolenta), others for their elegance (Diderma nigripes).

Some years ago a gigantic fungus, found growing from the woodwork of a tunnel near Doncaster, afforded a striking proof of the luxuriancy of subterranean vegetation. It measured no less than fifteen feet in diameter, and was, in its way, as great a curiosity as one of the colossal trees of California.

Even the plants that flourish in the darkness of caves have been rendered subservient to our use. The cultivation of the edible mushroom in spacious caverns or ancient quarries is practised to a great extent in the environs of Paris, at Arcueil, Moulin de la Roche, and St. Germain, but particularly at Montrouge, on the southern side of the city. The mushroom-beds are entirely underground, seventy or eighty feet below the surface, at a depth where the temperature is nearly uniform all the year round. These extensive catacombs, formed by long burrowing galleries, have no opening but by a circular shaft, to be descended by clambering down a perpendicular pole or mast, into the sides of which large wooden pegs are fixed, at intervals of ten or twelve inches, to rest the feet upon.

The baskets containing the ripe mushrooms are hoisted from below by a pulley and rope. The compost in which they grow consists of a white gritty earth, mixed with good stable manure, and is moulded into narrow beds about twenty inches high, ranged along the sides of the passages or galleries, and kept exquisitely neat and smooth. The mushroom sporules are introduced to the beds either by flakes of earth taken from an old bed, or else from a heap of decomposing stable manure in which mushrooms have naturally been engendered. The beds are covered with a layer of earth an inch thick, the earth being merely the white rubbish left by the stone-cutters above. They must be well watered, and removed after two or three months, when their bearing qualities are exhausted. In one of the caves at Montrouge alone there are six or seven miles of mushroom-bedding, a proof that this branch of industry is by no means unimportant.

While subterranean vegetation is exclusively confined to mushrooms, animal life of almost every class has far more abundant representatives, for plants are in general much more dependent on the vivifying influence of light.

The various animals which are found dwelling in caves may be subdivided into two groups; one, which, though preferring darkness, and spending a great part of its existence under the earth, yet often voluntarily seeks the light of day, or at least wanders forth at night; while the other is exclusively subterranean, and is never seen above the surface of the earth, unless by chance or when driven up by violence.

To the first group belong most of the insectivorous and rodent quadrupeds that dwell in self-made burrows, or pursue a subterranean prey, such as the armadilloes and the moles. The large family of the bats likewise love to sleep by day, or to hibernate in warm and solitary caves, where they are sometimes found in numbers as countless as the sea-birds which flock round some rocky island of the north. When Professor Silliman visited the Mammoth Cave (October 16, 1822), he everywhere saw them suspended in dense clusters from the roofs, though a large number had not yet retired into winter-quarters. In a small space, scarcely four or five inches square, he counted no less than forty bats, and convinced himself that at least one hundred and twenty find room on a square foot, as they held not only by the surface of the walls of their retreat, but by each other, one closely crowding over another. Such clusters are found in the interior of the cavern, which branches out in many directions as far as two miles from the entrance, so that a very superficial survey allows them to be counted by millions. Who, in these dismal regions, where no change of temperature or of light announces the various seasons, tells them that the reign of winter is past? who awakes them at the proper time out of the deep sleep in which they remain plunged for months? The same mysterious voice of instinct which regulates the migrations of the birds and the wanderings of the fishes, and which in this case, as in every other, is equally wonderful and incomprehensible.

In the class of birds we find many cave-haunting species. The pigeons like to nestle in grottoes, which also serve as welcome retreats to the moping owl; and various swallows and swifts breed chiefly in the darkness of caverns. One of the most remarkable of these troglodytic birds is the Guacharo, which inhabits a large cave in the Valley of Caripe, near the town of Cumana, and of which an interesting account has been given by Humboldt, who first introduced it to the notice of Europe.

The Gueva del Guacharo is pierced in the vertical profile of a rock, and the entrance is towards the south, forming a noble vault eighty feet broad and seventy-two feet high. The rock surmounting the cavern is covered with trees of gigantic growth, and all the luxuriant profusion of an inter-tropical vegetation. Plantain-leaved heliconias, and wondrous orchids, the Praga palm, and tree arums, grow along the banks of a river that flows out of the cave, while lianas, and a variety of creeping plants, rocked to and fro by the wind, form elegant festoons before its entrance. What a contrast between this magnificently decorated portal and the gloomy mouth of the Surtshellir, imbedded in the lava wildernesses of Iceland? As the cave at first penetrates into the mountain in a straight direction, the light of day does not disappear for a considerable distance from the entrance, so that visitors are able to go forward for about four hundred and thirty feet without being obliged to light their torches; and here, where light begins to fail, the hoarse cries of the nocturnal birds are heard from afar.

The guacharo is of the size of the common fowl. Its hooked bill is wide, like that of the goat-sucker, and furnished at the base with stiff hairs directed forwards. The plumage, like that of most nocturnal birds, is sombre brownish grey, mixed with black stripes and large white spots. The eyes are incapable of bearing the light of day, and the wings are disproportionately large, measuring not less than four feet and a half from tip to tip. It quits the cavern only at nightfall, especially when there is moonlight; and Humboldt remarks that it is almost the only frugivorous nocturnal bird yet known, for it does not prey upon insects like the goatsucker, but feeds on very hard fruits, which its strong hooked beak is well fitted to crack. The horrible noise made by thousands of these birds in the dark recesses of the cavern can be compared only to the wild shrieks of the sea-mews round a solitary bird mountain, or to the deafening uproar of the crows when assembled in vast flocks in the dark fir-forests of the North. The clamour increases on advancing deeper into the cave, the birds being disturbed by the torch-light; and as those nestling in the side avenues of the cave begin to utter their mournful cries when the first sink into silence, it seems as if their troops were alternately complaining to each other of the intruders. By fixing torches to the end of long poles, the Indians, who serve as guides into the cavern, show the nests of these birds, fifty or sixty feet above the heads of the explorers, in funnel-shaped holes with which the cavern roof is pierced like a sieve.

Once a year, about midsummer, the Guacharo Cavern is entered by the Indians. Armed with poles they ransack the greater part of the nests, while the old birds, uttering lamentable cries, hover over the heads of the robbers. The young which fall down are opened on the spot. The peritonÆum is found loaded with fat, and a layer of the same substance reaches from the abdomen to the vent, forming a kind of cushion between the birds’ legs. The European nocturnal birds are meagre, as, instead of feasting on fruits and oily kernels, they live upon the scanty produce of the chase; while in the guacharo, as in our fattened geese, the accumulation of fat is promoted by darkness and abundant food. At the period above mentioned, which is known at Caripe as the ‘oil harvest,’ huts are erected by the Indians with palm leaves near the entrance, and even in the very porch of the cavern. There the fat of the young birds just killed is melted in clay pots over a brushwood fire, and is said to be very pure and of a good taste. Its small quantity, however, is quite out of proportion to the numbers killed, as not more than 150 or 160 jars of perfectly clear oil are collected from the massacre of thousands.

The way into the interior of the cavern leads along the banks of the small river which flows through its dark recesses; but sometimes large masses of stalactites obstruct the passage, and force the visitor to wade through the water, which is, however, not more than two feet deep. As far as 1,458 feet from the entrance the cave maintains the same direction, width, and height of sixty or seventy feet, so that it would be difficult to find another mountain cavern of so regular a formation. Humboldt had great difficulty in persuading the natives to pass beyond the part of the cave which they usually visit to collect the oil, as they believed its deeper penetralia to be the abode of their ancestors’ spirits; but since the great naturalist’s visit, they seem to have abandoned their ancient superstitions, or to have acquired a greater courage in facing the mysteries of the grotto, for, while they would only accompany Humboldt as far as 236 fathoms into the interior of the cave, later travellers, such as Codazzi and Beaupertuis, have advanced with their guides to double the distance, though without reaching its end. They found that beyond the furthest point explored by Humboldt the cave loses its regularity, and has its walls covered with stalactites. In the embranchments of the grotto Codazzi found innumerable birds. It was formerly supposed that the guacharo was exclusively confined to this cave; latterly, however, it has also been found in the province of Bogota.

The discovery of animals adapted for perpetual darkness is but of modern date, and as the vast majority of caves have not yet been thoroughly explored by zoologists, the number of genera and species already known gives us reason to believe that future investigations will add considerably to their number. In the Adelsberg, Lueg, and Magdalena grottoes, which form but an inconsiderable part of the extensive cavernous regions of Carniola, seven exclusively subterranean insects, one spider, two scorpionides, one millepede, two crustaceans, one snail, and one reptile—in all fifteen different species of animals, belonging to no less than six different classes—have been found.

Among these dwellers of the dark, warfare is as rife as in the regions of light. Thus, in the recesses of the Grotto of Adelsberg, the cavern beetle (Leptodirus Hochenwartii) is persecuted and devoured by the scorpioniform Blothrus spelÆus, and by the eyeless spider (Stalita tÆnaria). The black and brown Leptodirus discovered in the Grotto of Adelsberg in 1831, by Count Hochenwart, is distinguished by long and delicate antennÆ and legs, and comparatively small translucent and smooth elytra. The unique specimen found at the time was unfortunately lost, and although twenty-five florins were offered to the cavern guides for one of these beetles, fourteen years passed before it was re-discovered in the same cave. Since then other collectors have been more fortunate, particularly Prince Robert KhevenhÜller, who, during his repeated visits to the Cave of Adelsberg, captured no less than twenty specimens of the Leptodirus.

Cautiously feeling its way with its long antennÆ, the beetle slowly ascends the damp stalactital columns, and accelerates its movements at the approach of a light. The greater number were found in the evening, thus giving reason for supposing that the Leptodirus is a noctural beetle, although it is hardly possible to conceive how the alternating influence of night and day can still be felt in these regions of darkness. The manner in which it is pursued by the eyeless Blothrus (discovered in 1833, by Mr. F. Schmidt), has been several times observed by Prince KhevenhÜller. He once saw one of these cavern scorpions slowly crawling along, stretching out its palpi in all directions, and evidently on the search. He immediately guessed that the animal was engaged in a hunting expedition, and soon found that he was not mistaken, for a fine Leptodirus was crawling about four feet higher on the opposite wall. For a long time the Prince left the two insects undisturbed, until he had thoroughly convinced himself that the movements of the Blothrus were evidently regulated by those of the Leptodirus, and that the former was, beyond all doubt, in pursuit of the beetle. A Leptodirus having been thrown along with a Blothrus into a phial, was immediately cut to pieces and devoured.

The eyeless cavern spider (Stalita tÆnaria), with brownish palpÆ and a snow-white abdomen, is not seldom found in the hollows of the stalactites, lying in wait for the unfortunate Leptodirus. On the surface of the earth spiders are frequently obliged to fast for a very long time; but in caverns where life is so sparingly distributed, the patience of the Stalita must be exemplary, even among spiders. Her appearance on the snow-white stalactital columns, where she only becomes visible when illumined by the full light of a taper,^[21] is very striking. Like a vision, she sweeps away in her ivory robe, accompanied by her increasing shadow, until she finally disappears in the darkness.

But the largest and most interesting of all the European cave animals is undoubtedly the Olm (Proteus anguinus; Hypochthon). This enigmatic reptile was first found in the famous Lake of Cirknitz, which, communicating with numerousnumerous subterranean caves, alternately receives and loses its waters through openings in the rock. After long and heavy rains the floods, which the hidden vaults are no longer able to contain, gush forth in foaming cataracts, and the lake, which generally forms but a long and narrow channel, then swells to at least three times its ordinary width. Sometimes, after a long drought, the contrary takes place, and the whole lake disappears under ground. Thus, from December 1833 to October 1834, not a trace of it was visible, so thoroughly had it concealed itself in its subterranean reservoirs, where its fishes, secure from the persecutions of man, multiplied in a remarkable manner. The Olm, which only casually comes to the light of day, along with the overflowing waters of the Cirknitz Lake, was first discovered in 1814, in one of its permanent subterranean abodes. The Magdalena or ‘Black Grotto’ situated about a league to the north of Adelsberg, slants abruptly into the bowels of the mountain. After a long and difficult passage over blocks of stone or through soft mud, a tranquil pool is at length reached, which rises or falls simultaneously with the waters of the Poik, and proves, by this reciprocal action, that, in all probability, all the numerous grottoes and subterranean river channels of this so strangely undermined country form but one vast and intricate network. It was in this pool, which no light illumines and no wind ever stirs, that numerous Protei were first discovered; but as hundreds of specimens have since found their way to the cabinets of naturalists, to be observed, dissected, or bottled up in spirits, their number has very much decreased, and the time is perhaps not far distant when they will be entirely extirpated in the grotto, where from time immemorial they had enjoyed an undisturbed security. The Proteus is one of those remarkable reptiles which breathe at the same time through lungs and gills, having on each side of the neck three rose-red branchiÆ, which it retains through life, as its lungs are but imperfectly developed. It has a long, eel-like body with an elongated head, a compressed tail, and four very short and thin legs. The skin is flesh-coloured, and so translucent that the liver and the heart, which beats about fifty times in a minute, can be distinctly seen underneath. In spite of its apparent weakness, it is able to glide rapidly through the water. Its four little legs remain immovable while swimming; they are only used for creeping, and then in a very imperfect manner. During rapid movements the gills swell and assume a lively scarlet colour; when quiet, they collapse and become white like the rest of the body. Sometimes the animal raises its head above the water to breathe, but pulmonary respiration evidently plays but a secondary part in its economy, as it can only live a very short time out of the water. The skeleton consists almost entirely of cartilage. The eyes, two little black spots, lie buried under the skin, and, as may well be imagined, are very imperfectly developed. Although more than a thousand specimens have been observed, yet but little is known about its mode of life, nor has it been ascertained whether it is oviparous or brings forth live young. In a captive state the Proteus is able to live for several years without any apparent food; but on fastening a small worm to the extremity of a thin stick, and holding it under the water close to the head of the reptile, it shoots rapidly towards it, swallows it with the same velocity, then ejects it again, and repeats this manoeuvre several times, until it finally retains the morsel. The untiring zeal of the German naturalists has discovered the Proteus in thirty-one different caverns, and ascertained seven distinct species, varying by their size, the form of the head, the position of the eyes, and the colour of the skin. Six of these species belong to the caverns of Carniola, and the seventh to those of Dalmatia. Two different species never inhabit the same cavern.

During the visit which the Archduke Ferdinand paid, in 1819, to the Magdalena Grotto, the most remarkable parts of the cave were brilliantly illuminated, so as to produce a magical effect. Charon’s boat, issuing from a dark recess, came gliding along over the black surface of the pool. The grim ferryman drew up his net before the august visitors, and presented them with six Protei that had been entangled in its meshes. Dr. Schmidl mentions part of the subterranean river in the Planina Cave, 1,715 fathoms from the entrance, as the spot where the Protei are most abundant. Near to a small cascade which the rivulet here forms over a reef, the waters absolutely swarm with them, and the light-coloured animals, darting about in all directions in the dark stream, afford a strange and picturesque spectacle. As the cavern is of most difficult access, they here enjoy a tranquillity rarely disturbed, and no doubt they have many other still more hidden retreats, to which man is incapable of penetrating. The best method for transporting the Proteus is now perfectly understood, and living specimens have been conveyed as far as Russia, Hungary, and Scotland. All that they need is a frequent supply of fresh water, and a careful removal of all light. Their food need cause no trouble, as the water contains all they require. It is recommended to lay a piece of stalactite from their native grotto in the vase in which they are transported. When resting or sleeping, they then coil themselves round the stone, as if tenderly embracing it. In this manner they have already been kept above five years out of their caverns. The guides to the Grotto of Adelsberg have always got a supply on hand, and sell them for about two florins a-piece.

On turning our attention from the grottoes of Carniola to those of the New World, we find, in the vast Mammoth Cave in Kentucky, a no less interesting animal creation, which, though different from that of the Austrian caverns, still shows a certain family resemblance, and affords another proof that a similarity of external circumstances always produces analogous forms of organic life. Thus, the two blind beetles which are found in the Mammoth Cave belong to the same genera (Anophthalmus and Adelops) that have also their representatives in the Grotto of Adelsberg. The largest insect is here a species of cricket, with enormously long antennÆ; there are also two small white eyeless spiders and a few crustaceans. The Mammoth Cave has no proteiform reptile to boast of, but a peculiar blind rat and a peculiar blind fish.

The cavern rat, which is tolerably numerous, but which, on account of its remarkable timidity, seldom shows itself, differs from the common or Norway rat, by its bluish colour, its white abdomen, neck, and feet, and its soft hair. It has large black eyes, like those of a rabbit, but entirely destitute of an iris, and uncommonly long whiskers, as if Nature had wished to indemnify it for the loss of sight by a more perfect development of the sense of touch. Although the eyes of this rat are large and brilliant, yet Professor Silliman convinced himself of their perfect insensibility to light. All proof is wanting that it ever visits the upper world.

The blind fish (Amblyopsis spelÆus) is now become tolerably rare from its having been so frequently fished out of the Lethe stream, as the subterranean river of the Mammoth Cave is called. Many physiologists have already made it the subject of their observations, and are generally of opinion that the Amblyopsis was not originally blind, but that, having found its way into the cave, it gradually lost its powers of vision. The celebrated naturalist Agassiz, however, being perfectly convinced that all animals existing in a wild state have been created within their actual bounds with all the peculiarities of structure which distinguish them at the present day, is of opinion that the blind fish and all the other blind animals of the Mammoth Cave are the aboriginal children of darkness, and have at no time been connected with the world of light.