Part 6

Three species of pine-leaves are mentioned by Darwin as being regularly drawn into the mouths of worm-burrows on the gravel-walk in his garden. These leaves consist of two needles, which are united to a common base, and it is by this point that they are almost invariably drawn into the burrows. As the sharply-pointed needles diverge somewhat, and as several are drawn into the same burrow, each tuft forms a perfect _chevaux-de-frise_. Many tufts were pulled up in the evening, but by the ensuing morning fresh leaves had taken their places, and the burrows again well protected. Impossible it would be to drag these leaves to any depth into the burrows, except by their bases, as a worm cannot seize hold of the two leaves at the same time, and if one alone were seized by the apex, the other would be pressed against the ground and resist the entry of the one that was seized. That the worms should do their work well, it was very essential that they drag the pine-leaves into their burrows by their bases, that is, where the two needles are conjoined. But how they are guided in this work was at first perplexing. The difficulty, however, was soon settled. With the assistance of his son Francis, the elder Darwin set to work to observe worms in confinement during several nights by the aid of a dim light, while they dragged the leaves of the aforementioned kinds into their burrows. They were seen to move the anterior extremities of their bodies about the leaves, and on several occasions when they touched the sharp end of the needle they suddenly withdrew as though they had been pricked, but it is doubtful that they were hurt, for they are indifferent to sharp objects, being known to swallow rose-thorns and small splinters of glass. It may be doubted whether the sharp end of the needle serves to tell them that is the wrong end to seize, for the points of many were cut off for the length of an inch, and these leaves were always drawn in by their bases and not by the cut-off ends. The worms, it seemed, almost instantly perceived as soon as they had seized a leaf in the proper manner. Many leaves were cemented together at the top, or tied together by fine thread, and these in the majority of instances were dragged in by their bases, which leads to the conclusion that there must be something attractive to worms in the base of pine-leaves, notwithstanding that few ordinary leaves are drawn in by their base or footstalk. Leaves of other plants, and also the petioles of some compound plants, as well as triangular bits of paper, dry and damp, were experimented with, and the manner of seizing the objects and bearing them into their burrows were as amusing as they were novel and interesting. The leaves and stems used were such as the worms had not been accustomed to in their respective haunts.

When the several cases experimented on are considered, one can hardly escape from the conclusion that some degree of intelligence is shown by worms in plugging up their burrows. Each particular object is seized in too uniform a manner, and from causes which we can generally understand, for the result to be attributed to mere chance. That every object has not been drawn in by its pointed end may be accounted for by labor having been saved by some being carried in by their broader ends. There is no doubt that worms are governed by instinct in plugging up their burrows, and it might be expected that they would have been taught in every particular instance how to act independently of intelligence. It is very difficult to judge when intelligence comes into play. The actions of animals, appearing due to intelligence, may be performed through inherited habit without any intelligence, although aboriginally acquired, or the habit may be acquired through the preservation and inheritance of some other action, and in the latter case the new habit will have been acquired independently of intelligence throughout the entire course of its development. There is no _à priori_ improbability in worms having acquired special instincts through either of these two latter means. Nevertheless it is incredible that instincts should have been developed in reference to objects, such as the leaves and petioles of foreign plants, wholly unknown to the progenitors of the worms which have acted in the manner just described. Nor are their actions so unvarying or inevitable as are most true instincts.

As worms are not controlled by special instincts in each particular case, though possessing a general instinct to plug up their burrows, and as chance is excluded, the next most probable conclusion is that they try in many ways to draw in objects and finally succeed in some one way. It is surprising, however, that an animal so low in the scale as a worm should have the capacity to act in this way, as many higher animals have no such capacity, the instincts of the latter often being followed in a senseless or purposeless manner.

We can safely infer intelligence, as Mr. Romanes, who has specially studied animals, says, only when we see an individual profiting by his own experiences. That worms are able to judge either before or after having drawn an object close to the mouths of their burrows how best to drag it in, shows that they must have acquired some notion of its general shape. This they probably acquire by touching it in many places with the anterior extremity of their bodies, which serves them as a tactile organ. Man, even when born blind and deaf, shows how perfect the sense of touch may become, and if worms, which also come into being in the same condition, have the power of acquiring some notion, however rude, of the shape of an object and their burrows, they deserve, it must seem to every sensible mind, to be called intelligent creatures, for they act in such a case in nearly the same manner as a man would under similar circumstances. That worms, which stand so low in the scale of organization, should possess some degree of intelligence, will doubtless strike everyone as very improbable. It may be doubted, however, whether we know enough about the nervous system of the lower animals to justify our natural distrust of such a conclusion. With regard to the small size of the cerebral ganglia, we would do well to remember what a mass of inherited knowledge, with some power of adapting means to an end, is crowded into the minute brain of a worker ant.

Two ways are adopted by worms in excavating their burrows. Either the earth is pushed away on all sides or it is swallowed by the animal. In the former case the worm inserts the stretched-out and attenuated anterior extremity of its body into any little crevice or hole, and the pharynx is pushed forward into this part, which consequently swells and pushes away the earth on all sides, the anterior extremity thus acting as a wedge. When placed in loose mould a worm will bury itself in between two and three minutes, but in earth that is moderately pressed down it often requires as many as fifteen minutes for its disappearance. But whenever a worm burrows to a depth of several feet in undisturbed compact ground, it must form its passage by swallowing the earth, for it is impossible that the ground could yield on all sides to the pressure of the pharynx when pushed forward within the worm’s body. Great depths are reached only during continued dry weather and severe cold, the burrows sometimes attaining to a depth of from seven to eight feet. The burrows run down perpendicularly, or, more commonly, obliquely, and are sometimes said to branch. Generally, or invariably as I think, they are lined with fine, dark-colored earth voided by the worm, so that at first they must be made a little wider than their ultimate diameter. Little globular pellets of voided earth, still soft and viscid, often dot the walls of fresh burrows, and these are spread out on all sides by the worm as it travels up or down its burrow, the lining thus formed becoming very compact and smooth when nearly dry and closely fitting the worm’s body. Excellent points of support are thus afforded for the minute reflexed bristles which project in rows on all sides from the body, thus rendering the burrow well adapted for the rapid movement of the animal. The lining appears also to strengthen the walls, and perhaps saves the worm’s body from being scratched, which would assuredly be the case when the burrows, as is occasionally observed, pass through a layer of sifted coal cinders. The burrows are thus seen to be not mere excavations, but may be compared with tunnels lined with cement. Those which run far down into the ground generally, or at least frequently, terminate in little chambers, where one or several worms pass the winter rolled up into a ball. Small pebbles and seeds as large as grains of mustard are carried down from the surface by being swallowed or within the mouths of worms, as well as bits of glass and tile, whose only use in their winter-quarters seems to be the prevention of their closely coiled-up bodies from coming into contiguity with the surrounding cold soil, for such contact would perhaps interfere with their respiration, which is effected by the skin alone.

After swallowing earth, whether for making its burrow or for food, the earth-worm soon comes to the surface to empty its body. The rejected matter is thoroughly mixed with the intestinal secretions, and is thus rendered viscid. After becoming dried, it sets hard. When in a very liquid state the earth is thrown out in little spurts, and when not so liquid by a slow peristaltic movement of the intestine. It is not cast indifferently on any side, but first on one and then on another, the tail being used almost like a trowel. The little heap being formed the worm seemingly avoids, for the sake of safety, the use of its tail, the earthy matter being forced up through the previously deposited soft mass. The mouth of the same burrow is used for this purpose for a considerable time. When a worm comes to the surface to eject earth, the tail protrudes, but when it collects leaves its head must protrude, and thus worms must have the power of performing the difficult feat, as it seems to us, of turning round in their closely-fitting burrows. Worms do not always eject their castings upon the surface of the ground, for when burrowing in newly turned-up earth, or between the stems of banked-up plants, they deposit their castings in such places, and even hollows beneath large stems lying on the surface of the ground are filled up with their ejections. Old burrows collapse in time. The fine earth voided by worms, if spread out uniformly, would form in many places a layer of one-fifth of an inch in thickness. But this large amount is not deposited within the old unused burrows. If the burrows did not collapse, the whole ground would be first thickly riddled with holes to the depth of ten inches or more, which in fifty years would grow into a hollow, unsupported place ten inches deep.

Hardly any animal is more universally distributed than worms. The earth-worm is found in all parts of the world, and some of the genera have an enormous range. They inhabit the most isolated islands, abounding in Iceland, and also being known to exist in the West Indies, St. Helena, Madagascar, New Caledonia and Tahiti. Worms from Kergulen Land in the Antarctic regions have been described by Ray Lankester, and Darwin has reported them as being found in the Falkland Islands. How they reach such isolated islands is quite unknown. They are easily killed by salt water, and it does not seem likely that young worms or their egg-capsules could be carried in earth adhering to the feet or beaks of land-birds, especially to Kergulen Land, for it is not now inhabited by any terrestrial bird.

We have seen that worms are found in nearly every part of the globe, that they are very numerous, as many as 348,480 having been found in an acre of rich ground in New Zealand, and that by the peculiar economy of their nature they are fitted to accomplish a great deal of good in the earth. They have played a more important part in the history of the world than most persons would at first suppose. In many parts of England, according to Darwin, a weight of more than ten tons of dry earth annually passes through their bodies and is brought to the surface in each acre of land, so that the entire superficial bed of vegetable mould passes through their bodies in the course of every few years; and in most parts of the forests and pasture-lands of Southern Brazil, where several species of earth-worms abound, the whole soil to a depth of a quarter of a metre looks as though it had passed through the intestines of worms, even where scarcely any castings are to be observed upon the surface. The upper crust is continually being eaten and ejected by them, thus aiding the fertility of the soil, as well as conveying water and air to the interior by the myriads of burrows which they drill. The vast quantities of leaves that they drag into their holes tend also to enrich the ground. Nor does their good end here. They cover up seeds, undermine rocks, burying them up, and to their labors is due the preservation of many ruins and ancient works of art. Numerous old-time Roman villas have been discovered beneath the ground in England, whose entombments were undoubtedly caused by the worms that undermined them and deposited their castings upon the floors, till finally, aided by other causes, they disappeared from sight.

When a wide, turf-covered expanse of earth is beheld, we would do well to remember that its smoothness, upon which so much of its beauty depends, is largely due to all the inequalities having been slowly levelled by worms. That all the surface-mould of any such expanse has passed, and will again pass, every few years through the bodies of worms is a marvellous reflection, and one which should not be lightly dismissed from the mind. The most ancient, as well as one of the most valuable of man’s inventions, is the plough. But long before man existed the land was in fact regularly ploughed, and still continues to be ploughed, by earth-worms. No other animal has played such a part in history as have these lowly-organized creatures. True it is that corals, which are still lower in the scale of animals, have performed more conspicuous work in the innumerable reefs and islands they have built in the great oceans, but their work is confined to the tropical zones, while that of the earth-worm is well-nigh universal. Verily it is by the little things in life that the Creator has erected the most stupendous monuments to show forth His infinite power and wisdom.

FIDDLER- AND HERMIT-CRABS.

Among our first acquaintances of the sea-shore are sure to be a number of merry little sprites which do not seem to have yet mastered the lesson of walking straight ahead. Their movements will be seen to be in a direction at right angles to that towards which the head points. It is a very interesting sight to watch these apparently one-sided creatures hurrying off in their lateral progression towards their burrows in the sand or mud, or in quest of food. Pass them, and you will be surprised to see how quickly some of them will reverse their motion, seemingly without so much as pausing to glance at their pursuer, their machinery appearing to have given out at one end, thus compelling them to reverse and travel back over their old courses.

These little Fiddler- or Calling-crabs, as they are termed, are the most pronounced offenders against the commonly accepted rule of proper walking. Scattered all over the salt marshes and mud-flats, at about high-water mark, may be noted their burrows, which are about as large as a thrust made by an umbrella point, and from which can be frequently seen the little animal peeping forth, preparatory to making a sally. At another part of the flat, where the noise of your footsteps has not given signals of danger, hundreds of crabblings are busy with their out-door occupations. Draw near to them, and away they scamper to their dwellings, males and females intermingled promiscuously, the former recognizable by the undue development of one of the claws, which is carried transversely in front of the head. When the animal is provoked, this claw is brandished in a somewhat menacing manner, which has been likened by some to the pulling of a violin bow, and by others to the action of beckoning or calling, and hence the names which have been applied to these eccentric creatures.

Have you a desire for a more intimate knowledge of the animal, take him up by the big claw, and you can now examine him without the least fear of incurring the proofs of his displeasure. Two bead-like, compound eyes, supported on long stalks, which can be readily withdrawn into the protecting shield of the carapace, will be observed. From the manner of this support, which allows of vision in almost every direction, the name of stalk-eyed crustaceans has been given to the group in which this structure is found. The two pairs of feelers, which you see in front of the eyes, are known as antennæ and antennules. They are of peculiar interest, for, aside from acting as feelers, they subserve the functions of smelling and hearing, the auditory apparatus being lodged in the base of the smaller pair. There are ten feet, and this is a character of importance, as it is a feature distinctive of the ten-footed, or decapod, crustaceans. At first sight it appears that the animal is devoid of a tail, but if you turn him over upon his back you will find a very short one tucked safely under the body. A comparison of our study of this crab with that of the lobster or cray-fish will show that the tail, or, more properly, the abdomen, is stretched out beyond the body proper, and that the elongation is in proportion to the length of the animal. Two distinct groups of ten-legged, stalk-eyed crustaceans are thus recognized, namely: the short-tailed forms, or crabs, and the opposite, or long-tailed forms, to which the lobster and shrimp belong, the hermit-crabs constituting an intermediate type.

Two species of the Fiddler, considerably resembling each other in color and ornamentation, are to be found upon our Atlantic Coast. The more common form, _Gelasimus vocator_, has a smooth, shining carapace, while that of _Gelasimus minax_ is finely granulated and in part tuberculated, the back of both appearing impressed with a figure very similar to the letter H. The latter, which appears to be a vegetable feeder, is the larger, its burrows not infrequently measuring one and a half inches in diameter. Estuarine regions, in close proximity to fresh water, rather than the tidal flats, are its habitat, and, in truth, it seems to be able to get along for weeks, and even months, without any absolute need of salt water.

In the excavation of their homes the Fiddlers throw up the pellets of moist earth by means of their anterior walking legs, depositing their burden usually at some little distance from the mouth of the burrow. As winter approaches, the domiciliary apertures are closed up, and the famine of winter is spent in a state of torpidity.

With the advent of spring they come forth from their brumal retreats, and soon concern themselves with the duties incident to the propagation of their kind. Two males are often observed contending in the fiercest manner for the possession of a female. They strike with the formidable claw most powerful blows, and I have often seen an opponent so completely claw-locked as to be unutterly unable to make any determined resistance. These contests last a long while, and finally conclude with the complete vanquishment of one or the other of the fighting parties, one or both sustaining at times some severe injury as the loss of an eye-peduncle or the joint of a limb. All the while the battle is waging, the female is a silent, passive spectator, and generally allies herself with the successful competitor for her affections. Even during the summer season, when the cares of brood-raising no longer command and enslave the attention of the female, these combats are still indulged in by the males, growing out of, as it would seem, the lingering smarts of old animosities festering in the memory. While these carcinological lords of the sea-side are eminently fitted for the sparring business, the whole physiognomy of their smaller, weaker partners bespeaks a life in which broils can have no part, a life devoted to peaceful and domestic pursuits.

Differing widely in structure and habits from the Calling-crabs, and affecting watery situations near the shore, are to be found the Hermit-crabs. These sprightly little animals, which are usually of small size, and have truly habits of their own, that stamp them at once as being original and distinctive, are a source of never-failing delight to the student of nature. They derive their name, as is well known, from the seclusion into which they cast themselves as the inhabitants of the shells of other animals, but it is probably not generally known, however, that the rights of tenantry are oftentimes exercised in the most arbitrary manner. Not always satisfied with a dead shell, the Hermit-crab has been seen to raid upon a living possessor and attempt to drag him from his home, in which operation the assailant is often assisted by a number of his fellows, each bearing with him his castle as defensive armor. True, the attack is probably made in many instances for the purpose of getting possession of the enemy as well as his belongings, and, however this may be, forcible possession is by them considered no misdemeanor.

The body of the Hermit-crab, in the greater number of species, is unprovided with a carapace, and, being soft and liable to injury, the animal is compelled to seek shelter usually in a snail-shell, winding himself about the coils, to the inner extremity of which he attaches himself by his modified posterior feet. So securely is he now intrenched that it is only with difficulty he can be withdrawn, retracting himself as he does further and further within cover of the shell. A sudden fracture of the apex of the shell, under which appears to be the most delicate part of the animal’s body, will generally effect a speedy dislodgment, the frightened Crab dropping from the aperture.

With his progressive development in size the Hermit requires frequent changes of abode. His methods in securing a new habitation are among the most interesting of his life. He is very circumspect in his movements, and will make several reconnoissances before he is fully satisfied with the conditions of his prospective home, retiring after each visit to the old shell.

Like many bipeds, he has his first of May, and so he goes house-hunting. He finds a shell. Will it do? He examines it within, feelingly if not courteously, to see whether it is to let. Satisfied on this point, he turns it over, then turns it round, to know if it will suit, the weight of the house being quite an item in the reckoning to one who is to carry it upon his back. All things being right, his mind is made up to move, and quickly, too, at that, lest he miss his chance through some more active fellow house-hunter who is on the alert. Out comes the body from the old house, and pop it goes into the new. The resolution to move, the surrender of the old house, and the occupancy of the new, were all effected within a fraction of a second of time.