CHAPTER V.

SUBTERRANEAN LIGHT-GIVERS.

In wandering through the fields in early morning, we often see little heaps of newly disturbed earth, and occasionally catch glimpses of reddish or pink bodies quickly withdrawing into little tunnels in the sod. These are the earthworms, considered the humblest of all animals; yet, as insignificant as they seem, they are among the most valuable aids to the agriculturist.

We may appreciate this by selecting a field at random in a good producing country, making a section down through the earth for several feet, when, if carefully done, we shall find innumerable tunnels formed by the worms, leading here, there, and everywhere. In fact, the upper crust of the earth is an endless maze of streets, lanes, and avenues. A naturalist has even attempted to calculate the number of these little workers, and has come to the conclusion that they average one hundred thousand to the acre; and in especially rich ground in New Zealand it was estimated that there were three hundred and forty-eight thousand, four hundred and eighty in a single acre. This vast body of worms is continually at work, boring this way and that, coming to the surface during the night, and retreating to greater depths during the day; and it is at once evident that their tunnels constitute a system of irrigation and ventilation for the upper crust. In other words, rain, instead of running off, enters the holes, and so penetrates the earth, thus being held for a longer time. Air also finds its way below the surface; so that the homes of the little creatures constitute storehouses for moisture.

But this is a very small part of the work accomplished. The worms are in league with the farmer; are, in fact, his unappreciated assistants, upon whose endeavors depends much of the success of his crops. They are continually swallowing the earth, and depositing it at the surface, and working it over and over. If I should ask my young readers to estimate the quantity of earth brought to the surface in a single acre in a year, I fear they would not place the amount as high as Mr. Darwin, who states that the vegetable mould thus transported in some places amounts to ten tons an acre. Think of it! If your ten-acre farm is in one of these favored localities, these silent workers, say to the number of a million, have ploughed up about one hundred tons of earth for you, giving you a fine top dressing.

The worms not only carry all this material to the surface, but they drag vast quantities of leaves and other matter down, that serve to enrich the soil and render it capable of producing larger crops. They cover up seeds and other objects to a remarkable extent; and a flat rock set upon the ground will soon become buried, through their means. Some of the most interesting parts of Roman villas found in England have been, according to Darwin, preserved in this way; the worms undermining them, and gradually heaping soil over the walks and slabs, until finally, aided by other causes, they disappeared beneath the ground.

The earthworms of Australia attain a large size,--sometimes several feet in length,--and have been seen climbing trees. Some casts found in India are a foot in length. The worms evidently live in complete darkness; but it is known that at certain times, and under certain conditions, they are luminous: so that a state of things may exist under the ground of which we have no conception, and the tunnels of these little creatures may be brightly illumined. We have never been so fortunate as to observe their phosphorescence, but Dr. Phipson says, “I distinctly remember witnessing, when a child, the phosphorescence of the earthworm. The light appeared connected with the mucus that covered the animal’s body.” And other naturalists have observed the light under certain conditions.

If they possess this property to a greater extent than we are now aware of, it must be a fatal gift, as the sharp little eyes of the mole, though not remarkable for their powers of observation, would probably catch the faintest gleam. These animals are continually upon the forage; and their appetites can be imagined from an actual experiment, which showed that two moles devoured in nine days 341 grubs, 193 earthworms, 25 caterpillars, and a mouse,--skin, bones, and all!

In the ocean depths we find that the marine worms, which constitute in the beauty of their appearance a magnificent assemblage, tunnel the upper crust of the bottom. Some years ago the moat or ditch surrounding Fort Jefferson, Fla., was pumped out, leaving a space nearly half a mile in extent, high and dry, which abounded in specimens that would have delighted the eyes of a specialist in any branch. Over this spot we had often, as a lad, enjoyed the venturesome fun of riding upon the backs of the great sea-turtles, kept there for the commissaries’ use, had fished in every nook and corner, and now the opportunity was presented for penetrating below the surface of the bottom.

Some little digging showed, that, for a foot or more from the surface, the sand and mud was fairly alive with a variety of worms, numerous to an extraordinary extent, and in many cases beautiful beyond description. This condition of things is true, to a greater or less extent, in many localities; the worms retiring to the mud and other retreats during the day, at night venturing out, and even swimming at the surface.

If we take a drop of water from any ditch or pond, or even from the stem of a flower that has been standing in a vase, and place it under a microscope of even ordinary power, we shall find that it is a world of itself; a vast ocean, in fact, to the many forms that live there. Chief among these drop inhabitants, we notice numbers of little creatures that attract attention immediately. They resemble tall hats without brims, or crystal bags with fringed edges. And that they are busy bodies is at once evident, as they swim along at a wonderful rate of speed, eating as they go, keeping their fringes or _cilia_, which appear like so many arms, in perpetual motion; now bumping against each other, forcing their way among crowds of different animals, and always appearing full of life and energy.

These little creatures, invisible to the naked eye, are minute worms, or Rotifers; and among them we find some interesting light-givers. The _Synachata_ is one; and others described by Ehrenberg, the largest being about one-eighth of a line in size, present a striking appearance under the glass in a dark room,--the little bags, seemingly at a white heat, darting about in every direction.

As small as are these wonderful creatures, they are well worthy of study; and even those not interested in natural history will find that the stems of their flowers, or the water in the vase, contain more wonders than they had dreamed of,--a single drop that can be lifted upon a pin-head being sufficient for the purpose.

The little hat-like form, _Hydatina senta_, already referred to, is remarkable for the rapidity of its increase. The eggs are laid or deposited within a few hours of the time they are first seen within the transparent parent, and twelve hours later the young break from the shell and appear; so that in a comparatively few days the descendants of a single animal might possibly far exceed the population of the United States. The larger worms are with hardly any exception ornamented in some remarkable way, and in many the splendors of their decorations must be seen to be appreciated. The radiating coronets of _Serpulæ_[30] are of the most delicate and beautiful description, abounding in bands and markings of striking hues. _Pectinaria_ has upon its head a pair of combs that might be burnished gold; while _Eunicedæ_ and _Nereidæ_[31] have equally resplendent decorations.

These charms of color, and they are of great variety, are seen by day; but at night many of these creatures assume the gift of phosphorescence, adding to the long list of marine light-givers that have been previously referred to. In four other families[32] are found the most beautiful light-givers of the group. Assuming that we have a certain species of the first mentioned in the aquarium, we may prepare for an extraordinary display. It is now snugly coiled up under a stone, perhaps fast asleep, and giving no evidence of its wondrous gift. Now touch it with the narrow handle of the dip-net, and a seeming electric spark is given out. But there is no electricity here: the light is a phosphorescent protest, and rapidly passes from scale to scale, until the whole animal stands out like a vivid shield of light against the bottom, glowing with the mysterious flame.

If the worm is greatly disturbed, we are presented with a unique method of protection. Upon feeling the blow or attack, the light becomes intense, and flashes quickly from segment to segment, and along all the series of _elytra_; and, as the animal darts away, one or more of the scales become disconnected and are left behind, a luminous spot, to attract the attention of a possible follower, while the worm itself escapes.

Nearly all the phosphorescent worms are rapid swimmers, and noted for their agile movements; and, as their scales are very readily disconnected, we may imagine in some cases a worm darting off and leaving a shower of sparks behind. In these worms the light is usually green.

We have seen that one of the deep-sea Crustaceans has phosphorescent bands upon its feet; and in the _Syllidæ_, a family which contains some remarkable worms, we find that the luminosity is confined to the under surface of the feet. In _Chætopterus_[33] a bright flashing light is emitted from the posterior feet, while a far more brilliant one glows at a point on the dorsum between the lateral wings of the tenth segment. The mucus of the animals appears to be the seat of the luminosity, and not only encircles the worm with an aureola of phosphorescence, but pervades the surrounding water with a rich bluish purple light, so vivid and brilliant that the medium in which the light-giver lives seems to have ignited, and to be slowly consuming its dependents.

[Illustration:

PLATE VII.

BURROW OF PHOLAS.

SEA PEN. (_Pennatula._)]

It has been noticed, according to W. C. McIntosh, that an odor accompanies this display, resembling somewhat that produced by phosphorus in combustion. We have noticed that many worms have a peculiar odor when handled, though not quite of this character.

The most brilliant of all these light-givers is _Polycirrus_, which emits over its entire surface a vivid pale-bluish light, marking it as one of the most beautiful of its kind; while _Sagitta_ and many more add to the wonders in this generally considered uninteresting group of animals.[34]