When a Star-fish is alarmed, or finds itself in strange quarters, it will be seen to curl up the tips of its rays, and there under the point of each ray will be found a thick red spot seated on the extremity of a nerve, and having in it as many as from one hundred to two hundred crystal lenses surrounded by red cells. With such a highly-developed eye, which is far better than the jelly-fish enjoys, it is no wonder that the Star-fish is so quick in discerning food, or enrages the fisherman by the discovery of the bait which he had intended for other animals, for it turns out that this stupid-looking animal is more wide-awake than it is given credit for. Sometimes, as in the beautifully delicate Star-fish, called the “Lingthorn,” a soft lid, or feeler, hangs over the eye-spot, which gives to the creature a curiously intelligent look, but in the case of our common form this lid is notably absent.
From all that has been written it must be evident that our first walking animal is by no means a poor or feeble creature. He has a chain armor woven into his leathery skin, with sharp, pointed spines, and snapping, beak-like claws to protect him; an excellent digestion and a capacious mouth to feed his greedy stomach, and a fine array of nerves, quick feeling and eyesight, and a wonderful apparatus for moving over the ground. When it is added to all these possessions the ability to close over the wound in the case of a lost ray and the growing of a new one, we see that his powers of living satisfactorily are by no means insignificant. But this curious walking apparatus of the Star-fish is far from being perfect in all his relations. They do not all walk by means of suckers any more than all sponge-animals build toilet sponge, or all slime-animals make chambered shells. Sure, the Rosy Feather-stars, for example, have no use for feet-tubes, as their lives are generally spent upon the rocks or nestled in bunches of sea-weed. Brittle-stars, as these are called, though closely related to the Star-fishes, are not easily confounded with them, for their arms are found to radiate from a clearly defined central disk, and there is no prolongation of their stomachs and ovaries into their interiors. The tube-feet pass out from the plates along the sides of the arms, instead of from the under surface as in the Star-fishes proper, and probably serve merely as a help for breathing, locomotion over the sands being effected by their long flexible arms. Their home is chiefly among the tangle and eel-grass, where their protecting covering affords them security from their many enemies.
EARTH-WORMS IN HISTORY.
Earth-worms are found throughout the world. Though few in genera, and not many in species, yet they make up in individual numbers, for it has been estimated that they average about one hundred thousand to the acre. Our American species have never been monographed, which renders it impossible to judge of their probable number. Their castings may be seen on commons, so as to cover almost entirely their surface, where the soil is poor and the grass short and thin, and they are almost as numerous in some of our parks where the grass grows well and the soil appears rich. Even on the same piece of ground worms are much more frequent in some places than in others, although no visible difference in the nature of the soil is manifest. They abound in paved court-yards contiguous to houses, and on the sidewalks in country towns, and instances have been reported where they have burrowed through the floors of very damp cellars.
Beneath large trees few castings can be found during certain parts of the year, and this is apparently due to the moisture having been sucked out of the ground by the innumerable roots of the trees, an explanation which seems to be confirmed by the fact that such places may be observed covered with castings after the heavy autumnal rains. Although most coppices and woods support large numbers of worms, yet in forests of certain kinds of tree-growths, where the ground beneath is destitute of vegetation, not a casting is seen over wide reaches of ground, even during the autumn. In mountainous districts worms are mostly rare, it would seem, a circumstance which is perhaps owing to the close proximity of the subjacent rocks, into which it is impossible for them to burrow during the winter, so as to escape being frozen. But there are some exceptions to this rule, for they have been found at great altitudes in certain parts of the world, and especially is this so in India, where they have been observed to be quite numerous upon the mountains.
Though in one sense semi-aquatic animals, like the other members of the great class of Annelids to which they belong, yet it cannot be denied that earth-worms are terrestrial creatures. Their exposure to the dry air of a room for a single night proves fatal to them, while on the other hand they have been kept alive for nearly four months completely submerged in water. During the summer, when the ground is dry, they penetrate to a great depth and cease to work, just as they do in winter when the ground is frozen. They are nocturnal in their habits, and may be seen crawling about in large numbers at night, but generally with their tails still inserted in their burrows. By the expansion of this part of the body, and with the aid of the short reflexed bristles with which they are armed inferiorly, they hold so securely that they can seldom be withdrawn from the ground without being torn in pieces. But during the day, except at the time of pairing, when those which inhabit adjoining burrows expose the greater part of their bodies for an hour or two in the early morning, they remain in their burrows. Sick individuals, whose illness is caused by the parasitic larvæ of a fly, must also be excepted, as they wander about during the day and die on the surface. Astonishing numbers of dead worms may sometimes be seen lying on the ground after a heavy rain succeeding dry weather, no less than a half-hundred in a space of a few square yards, but these are doubtless worms that were already sick, whose deaths were merely hastened by the ground being flooded, for if they had been drowned it is probable, from the facts already given, that they would have perished in their burrows.
After there has been a heavy rain the film of mud or of very fine sand to be seen over gravel-walks in the morning is often distinctly marked with the tracks of worms. From May to August, inclusive, this has been noticed when the months have been wet. Very few dead worms are anywhere to be seen on these occasions, although the walks are marked with innumerable tracks, five tracks often being counted crossing a space of only an inch square, which could be traced either to or from the mouths of the burrows in the gravel-walks for distances varying from three to fifteen yards, but no two tracks being seen to lead to the same burrow. It is not likely, from what is known of the sense-organs of these animals, that a worm could find its way back to its burrow after having once left it. They leave their burrows, it would seem, on a voyage of discovery, and thus they find new sites for the exercise of their powers. For hours together they may often be seen lying almost motionless beneath the mouths of their burrows. But let the ejected earth or rubbish over their burrows be suddenly removed and the end of the worm’s body may be seen rapidly retreating.
This habit of lying near the surface leads to their destruction to an immense extent, for, at certain seasons of the year, the robins and blackbirds that visit our lawns in the country may be observed drawing out of their holes an astonishing number of worms, which could not be done unless they lay close to the surface. But what brings the worms to the surface? This is a question whose answer cannot be positively asserted. It is not probable that they behave in this manner for the purpose of breathing fresh air, for it has been seen that they can live a long time under water. That they are there for the sake of warmth, especially in the morning, is a more reasonable supposition, which seems to be confirmed by the fact that they often coat the mouths of their burrows with leaves, apparently to prevent their bodies from coming into contact with the cold, damp earth, and by the still other fact that they completely close their burrows during the winter.
Some remarks about the structure of the earth-worm now appear apropos. Its body consists of from one hundred to two hundred almost cylindrical rings, each provided with minute bristles. The muscular system is well developed, thus enabling these animals to crawl backwards as well as forwards, and to retreat by the help of their affixed tails into their burrows with extraordinary rapidity. Situated at the anterior end of the body is the mouth. It is furnished with a little projection, variously called the lobe or lip, which is used for prehension. Behind the mouth, internally located, is a strong pharynx, which is pushed forwards when the animal eats, corresponding, it is said, with the protrudable trunk of other Annelids. The pharynx conducts to the œsophagus, on each side of the lower part of which are placed three pairs of large glands, called calciferous glands, whose function is the secretion of carbonate of lime. These glands are very remarkable organs, and their like is not to be found in any other animal. Their use is connected in some way with the process of digestion. The œsophagus, in most of the species, is enlarged into a crop in front of the gizzard. This latter organ is lined with a smooth, thick chitinous membrane, and is surrounded by weak, longitudinal, but powerful transverse muscles, whose energetic action is most effectual in the trituration of the food, for these worms possess no jaws, or teeth of any kind. Grains of sand and small stones, from the one-twentieth to the one-tenth of an inch in size, are found in their gizzards and intestines, and these little stones, independently of those swallowed while excavating their burrows, most probably serve, like millstones, to triturate their food. The gizzard opens into the intestine—a most remarkable structure, an intestine within an intestine—which runs in a straight line to the vent at the posterior end of the body. But this curious structure, as shown by Claparède, merely consists of a deep longitudinal involution of the walls of the intestine, by which means an extensive absorbent surface is secured.
Worms have a well-developed circulating system. Their breathing is effected by the skin, and so they do not possess any special respiratory apparatus. Each individual unites the two sexes in its own body, but two individuals pair together. The nervous system is fairly well developed, the two nearly confluent cerebral ganglia being situated very close to the anterior extremity of the body.