Few groups of animals differ so much in general appearance as the worms. Some resemble miniature snakes; others are flat, some are like needles, one lives in a cell; another stays in the tissue of some animal, while certain others infest the soil. Almost everywhere, on land and in the sea, under nearly all conditions, we shall find these remarkable creatures, which may be briefly described as animals having a head, tail, and upper and lower surfaces, and made up of a great many rings, or segments. In them we find an approach to the higher animals. Thus they have a heart, with red or green blood, breathing organs, though many breathe through the body walls, and a nervous system consisting of a minute brain in the upper portion of the small head.

All the worms deposit eggs, and nearly all are remarkable for the wonderful changes through which they pass before they attain maturity. This is well illustrated in a planarian worm (Fig. 60), which seems to require the presence of another animal to enable it to complete its development. The little creature which breaks from the egg (A) is a free-swimming creature surrounded by cilia or hairlike swimming organs. By these it moves through the water, and with strange instinct searches for some animal, generally a snail, which it enters. There it becomes surrounded by a sack and produces a little creature called the nurse (b), which soon grows to resemble the tadpolelike creature (C), which is filled with small egglike or germlike objects (a). It now changes into a wormlike creature (D), in which the germs have assumed the shape of worms (a), and soon breaks forth as a little form with a tadpolelike tail (E)—a remarkable performance. But the end is not yet; another animal is necessary to complete the change. Swimming about, the little creature is swallowed by some animal in drinking, and finds its way to the liver, where it lives, the tail being lost. The animal now changes into a perfect flukeworm (F), which finally leaves the animal or host and lays eggs in the water; these pass through the same wonderful transformation. The flukeworms (Fig. 61) are disagreeable flat creatures, not often seen, the marine forms attaining large size.

Many of the worms are parasites living upon other animals. The thorn-headed worm (Fig. 62) is an example. Who has not heard the story of the living horsehair? Almost every country newspaper has told the story, that some farmer after washing his horses had found several hairs taken from the horse's tail which "were alive," and to prove the story the farmer produces the "living horsehair" which is a remarkable imitation of the long hair of a horse's tail. But the hair is a well-known worm (Fig. 63) called Gordius aquaticus. It is almost exactly like a horse's hair, two or three feet in length, and found coiled up in ponds or snugly tucked away in the interior of a beetle or grasshopper which it has seized upon as a host. The deadly Trichina spiralis belongs to this group (Fig. 64). If the vinegar bottle is examined, in what is popularly called the "mother" at the bottom, still another member of the family will be found. This is a minute round worm almost invisible to the naked eye. It is very active and disagreeable to contemplate, living in the sour, fiery liquid.

In this group are many dangerous worms, as the guinea worm of remarkable length. While nearly all worms are disagreeable creatures, a few are very beautiful. Such are the rotifers or wheel animalcules (Fig. 65). These are the smallest and most active of the tribe of worms. To be found they must be sought in a drop of standing water, and as they are rarely ever over one thirty-sixth of an inch in length, a microscope is necessary. Among the throng of wonderful creatures one will be seen seemingly rolling over and over like a barrel, a minute whirling Dervish of the water. The rotifers assume a variety of shapes. One is a typical worm, another darts along by the aid of two circlets of cilia which vibrate so rapidly that the illusion of rolling is produced. No more wonderful creatures than these little worms are known, and they well repay the study required to know them well. Some of them are fixed and unable to swim, and many of the stories of spontaneous generation are due to the faculty these minute rotifers (often but three one hundredths of an inch in length) have of enduring almost any amount of drying. Thus if a pond is dried up by the sun, the rotifers seem to be able to lie dormant for a long time, and when a rain falls in the locality for the first time in years, the pool is at once peopled with rotifers which awaken from their long sleep. When it is known that Ehrenberg, the German naturalist, found that a certain species produced sixteen million young in less than two weeks, it is easy to understand how quickly a new pond might become rapidly equipped with a large population.

It is a singular fact that myriads of worms are seen daily, but are not known as such. These are the minute and beautiful Polyzoans (Fig. 66). They are marine animals, grow in colonies, and look like delicate seaweeds. They are often called moss animals. At the seashore we shall find the rocks and particularly the broad fronds of kelp near shore often encrusted with a delicate, beautiful tracery of pure white. In California I have found the kelp leaves at the surface covered with it, having the appearance of being coated with silver. Beneath the glass it develops into a beautiful tracery filled with cells. When magnified these cells are seen to resemble Figure 67, each one having its worm, which seems to blossom like a flower. These worms are minute imitators of corals, as they form a corallike structure, the worms having the faculty of secreting lime, as do the corals, yet they are much higher in the scale of life. One of the common seaweeds of the seashore is the sea mat or Flustra. No one would suspect it of being other than a beautiful marine plant with large leaves or branches, and many a collection of "seaweed," preserved through many years, contains the Flustra arranged among the real "plants" of the sea. But Flustra is merely a colony of worms. The minute spots seen upon it when enlarged beneath a microscope resemble so many cells of carbonate of lime secreted by the worms of the community or colony. Another species of Flustra is shown in Figure 68, and a part of the skeleton of the colony or of each cell is the peculiar bird's head which has a beak. This beak, even after the death of the worm, is seen to open and shut, snapping continually, much quicker than the little pincerlike objects we have seen in the sea urchins. The use of the so-called bird's head is not well understood.

This Flustra (Fig. 69) is very beautiful, forming a delicate little plantlike form about an inch and a half in size. But the crowning glory of these worms, as shown in the figure, is the circular crown of tentacles by which food is grasped as it passes by. Any one who has collected fossils in what is known as the Trenton limestone is familiar with the little fossil shell called Lingula, of which two thousand species are known. Curiously enough this little shell has come down to us to-day, and in Figure 70 we see the living Lingula of our waters with its long stem by which it fastens itself in the sand. Lingula resembles a small clam shell, has two perfect shells, and probably holds a place in many collections as a shell; yet Lingula is a worm which secretes a two-valved, unhinged shell, that is an almost perfect imitation of a bivalve mollusk. In the Santa Catalina Channel, California, from water six hundred feet in depth, I have dredged shells resembling those in Figure 71. They hung upon rocks in clusters, and were very striking in their rich colors of yellow, red, etc. In shape these Terebratulas, also common among the fossil shells, resemble ancient Roman lamps, and hence are called lamp shells. They too are worms, however, and many more shell makers called brachiopods. The "wick," a muscular stalk or byssus, becomes firmly attached to some object at the bottom. But in the instance of the little Lingula the stalk or anchor rope merely passes between the curious shells. If the latter are opened, we find a singular bridge or limy framework which is intended to support the soft parts of the bridge, a very conspicuous feature of which are what are called arms, long, ribbonlike, fringed processes (a) which are coiled up in the shell and serve as breathing organs and to obtain food as well. They can be extended some distance from the shells. The curious frame upon which they rest is well shown in Figure 72. It is on record that during the Sikh rebellion an entire English regiment was put to flight by a force of worms. The troops were marching through a forest when land leeches began to fall from every branch and leaf, dropping in such vast numbers that the men were almost crazed by the vicious bloodsuckers; hence they broke and ran for clear ground, where they could rid themselves of the terrible pests. Semper, the naturalist, states that he was driven from the forests of Luzon by these leeches, which fell upon him like dew. The ordinary leech of commerce (Fig. 73) belongs to this group. It has a sucking mouth, which bears three teeth. It was once much used by physicians for bleeding purposes, in fact, the animal derives its name from the fact that medical men in England were formerly called leeches. The leech had a high commercial value, over seven million being used in London in a single year, valued at ten dollars a thousand. Leech raising is a regular business in Russia, Bohemia, and Hungary.

The best known of all worms, perhaps, because all boys are fond of fishing, is the angleworm or earthworm (Fig. 74), which can be found where the earth is rich and moist. This worm is really a beautiful object, being highly iridescent, flashing a thousand hues in the sunlight to which it has a decided objection, as the heat soon dries it up. The ringed or segmented arrangement is easily observed as it moves along. By this marvelous arrangement a worm can either stretch itself out to an inordinate length, or telescope itself until it can hardly be recognized as a worm. There are several interesting features about earthworms which ordinarily escape the notice of even the angler. One is its feet, which differ from those of any other animal. They are very minute, and are bristles, each segment or ring being supplied with four. Another peculiarity of the earthworm is that instead of hunting out food in the earth it swallows the earth as it meets it, allowing the animal matter to be absorbed within. It then casts up the earth, which are the little mounds of mold found in the grass or turf every morning. This habit has made the worm a valuable aid to the farmer in preparing the soil, filling it with tunnels and constantly bringing new earth to the surface and turning it over. The amount of earth moved in this way was made a special study by Charles Darwin. In the year 1842 he spread a field with broken chalk, and after twenty-nine years examined it and found that the chalk in that time had been buried seven inches by the worms.

This gives us some idea of how important a factor these humble creatures are, working mainly at night, in burying the works of man. It is evident that in two or three centuries portions of buildings could be concealed. In England numbers of ancient Roman villas have been discovered, beautiful floors and foundations of ancient buildings which have been lost to sight by being covered by these night workers. To give an adequate idea of the work they accomplish, Darwin says that the amount of vegetable mold brought to the surface in a single year amounts to ten tons to a single acre. They rarely descend below six feet, and Darwin estimated that in favorable localities there are 100,000 in every acre. In New Zealand 348,480 have been found in a very rich acre. The worms eat the earth, and drag leaves and soft twigs into their holes at night. They plant seeds and bury stones. Some of the casts of giant worms of India are a foot in length. They live entirely beneath the ground, lining their burrows with very soft fine earth, which appears to be powdered for the purpose. All their operations are carried on at night, when they come to the surface and eject the casts. They have a habit of lying near the surface at the entrance of their burrows, a fact which the birds have discovered, robins and mocking birds particularly being very clever in hunting them out.

One of the most remarkable features of these worms is their phosphorescence, which I have found is more brilliant than that emitted by any other animal. Crossing an orange grove in southern California one dark and rainy night in January, I stumbled over a clod of earth, and if I had kicked a mass of live coals, the result could not have been more marked, as flashes of vivid light darted in every direction with the earth, caused by several earthworms which had exuded so much phosphorescent matter that it had pervaded the entire mass of surrounding soil. The phenomenon on a small scale can often be seen in southern California, especially in winter, when the ground is moist and wet.

Probably the most beautiful of all worms are those of the sea, the marine forms found everywhere from the mud banks to the long fronds of kelp washed by the foaming sea. Perhaps the most gorgeous creature taken from deep water is Aphrodite, several inches long, an inch across, and about the size of a mouse. The worms are provided with an array of iridescent bristles, so beautiful as to appear artificial, blazing with golden lights. Some of these worms are covered with strange and brilliantly colored streamers, as Cirratulus (Fig. 75). Others are long and slender, as Nereis (Fig. 76), a very common form alongshore. It is sought after by fishes with good appetites, and often caught, despite the fact that it has four eyes, four hundred paddles, and fierce jaws for seizing prey. Nereis lives in the sand in a tunnel. It has a habit of coming out at night and swimming abroad, when, creating a blaze of light, it becomes a very conspicuous object and is quickly caught by some wandering fish. These worms are among the most brilliant of all light givers; not alone for the intensity of light, but for its variety in tint and color. The most remarkable light givers are PolynoË, Syllis, ChÆtopterus, and Polycirrus. The first-mentioned emits a green light at the attachment of each scale. In the second the feet are light givers and emit a blue light. In the third the light blazes on the back at the tenth joint alone. The last is a worm of fire, the strange, little understood light blazing over its entire surface, a vivid blue.

I was once sitting on the shore of Avalon Bay in southern California when, in the darkest corner in the shadow of a high cliff, I saw, two hundred feet away, what appeared like candle lights floating upon the surface. Rowing a boat to the lights, I found that each one came from a spot of phosphorescence floating on the surface. When it moved, as it often did, phosphorescence streamed away in its wake. When taken in my hand the latter became bathed with the light which ran from the invisible animal. I succeeded in capturing one entire light, but could not make out the animal. Soon I noticed lights upon the bottom in water five feet deep. They appeared to be as large as saucers, but grew rapidly in size until they were as large as dinner plates, then the yellow light gradually diminished until it was not larger than a hazelnut, and came wriggling upward in a zigzag of fire, finally reaching the surface and resting, as one of the peculiar lights I had seen so far away. I captured several, and in the morning found that my light giver was a minute sea worm not half an inch in length. When discovered, the little animal was leaving its burrow or cave in the sand for a nightly swim at the surface.

Many of the most beautiful of the marine worms are cell builders (Fig. 77). In some the worms secrete a tube of carbonate of lime. In others the den is made of bits of sand. I found on the Florida Reef many remarkable examples of the latter. The nest or tube was built among the seaweed, several inches above the bottom, and would naturally be a conspicuous object; but here the intelligence of the little creature is seen, for it covers the outside of the column with the plates of a lime-secreting seaweed, which look like shingles, and mounts upon the upper portion of the column a green bit of seaweed. This is glued to the tube and so arranged that it falls over the entrance and closes it, thus serving the purpose of a door and making the tube mimic a bit of sea grass. The worm lifts the grass door when it comes out.