My Tropic Isle - Edmund James Banfield (little bear else holmelund minarik .txt) 📗

are abundant, and among them certain genera which might be taken as apt illustrations of the more significant facts of evolution. Studying them, the parting of the ways between two distinct orders, each having a conspicuous feature in common while differing in appearance and habits generally, is made strangely plain, and I propose in my unversed way to demonstrate the line of upward development in a few examples.

Accepting as a primitive form that deplorably thin, phantasmal worm which excavates in the ooze an appropriately narrow shaft indicated by a dimple, or, in some cases, a swelling mound with a well-defined crater and circular pipe, the ascent of the genealogical tree is not beset with any great difficulty. These worms are grey in colour and shoddy in texture, merely a tough description of slime with a crude head and long, simple filaments. The sides of the shafts are smooth, and on the least alarm the nervous inhabitant retracts with surprising alertness. Slightly superior in grade, but in uninterrupted succession, is a similar worm which solidifies its shaft with a kind of mortar and carries it up above the level of the ooze about an inch or so--a crude effort in the direction of the acquirement of some ease of circumstance. These flue-like projections are more frequent on the verge of the sandy beach.

The next in order--still slim, though of a slightly more robust habit of body--has acquired the art of spinning (caterpillar-like) a cocoon, and of causing to adhere to the exterior thereof grains of sand and minute chips of shell. Though this vestlet is very frail and though the sandy outer coat is liable to drop off (when it collapses altogether), it seems to me to indicate distinct progress, a successful accomplishment in the direction of isolation, independence, and security. Does it not signify that the animal has a certain perception of the knowledge of good and evil such as dawned upon Eve as she ate the diverting apple? Eve forthwith took to fig-leaves; the slim worm knitted a shoddy wrapper and reinforced it with grains of sand when it realised that there was something better than slush for a dwelling. The sandy coverlet is evidence of the gift of discrimination.

A still more highly endowed relation spins a similar fabric, upon which are loosely agglutinated numbers of small dead shells, grit, and even opercula a quarter of an inch in diameter. In weight, size, and number of its constituents this exterior armour is altogether disproportionate to the extreme tenuity of its foundation. Too unsubstantial to sustain its own weight, it sprawls, like the track of a tipsy snail, indeterminately, slowly developing its sinuosities over the irregular surface of a rock, and slightly adherent thereto, throughout its whole length. Of this there seem to be several nicely shaded grades, some in the form of galleries laboriously built of a mixture of mud and sand, and each indicating superiority to the naked denizen of the clement mud. They seem to be superior in appearances also, for some of the animals display brightly coloured plume-like tentacles, long and capable of being ostentatiously fluttered.

The individual worm next to be described typifies such a wonderful advance that it might almost be designated a subsequent and intrusive sport, no marked are the distinctions it exhibits. It is one of the shell-binders (PECTINARIA), but its mansion of mosaics is unique and beautiful. In the universal struggle for place, self-preservation, and food, the animal has acquired a higher order of intelligence and keener perceptions of safety and of the niceties of life than its fellows. Living in sand and mud, in obedience to some gracious instinct, it gathers numbers of small shells, grit, and fragments of coral wherewith to construct a tube, somewhat similar in shape to the horn of cornucopia, and from three to six inches long. The materials are cemented together in accordance with a symmetrical design, the interior being lined with a transparent substance, which, when dry, is readily separable from the casing! This creature accomplishes by calculation, choice, and dexterity that which a subtle chemical process does unconsciously for the more advanced mollusc, and that it practised the art of the interlocking of atoms ages before the birth of Macadam can scarcely be doubted.

My imagination loves to dwell on the perceptive faculties possessed by this lowly creature, a creature soft and delicate, merely such and such a length of gelatinous substance, slightly stiffened and toughened and graced with a pair of tentacles glittering like tinsel extended from a marvellously constructed tube.

In certain structural details the animal (which in appearance has greater resemblance to a caterpillar than a worm) is even more remarkable than the ornate dwelling it constructs, for it is an actual though living prototype of the fabled race (catalogued by Othello with the anthropophagi)--


"Whose heads
Do grow beneath their shoulders."


The paradox exists, not as a whim or grimace on the part of Nature but for a definite and vital end. In default the animal would be unable to obey the first law of Nature--self preservation--for it is soft-bodied and its dwelling has the serious defect of being open at both ends. In such plight lacking special organs it would be at cruel advantage in the struggle for existence. The posterior segment of the body is therefore developed into an operculum-like organ, smooth and of horny texture, which closes the narrow end of the tube. The other extremity is more elaborately guarded, the anterior segment being fringed with a frontal membrane, while the second segment forms a disc, the minute mouth orifice with the true tentacles and gills being debased to the third segment.

Confronted by danger, the animal closes its front door by retracting until the disc presses immovably against the circumference of the tube, the retraction being so sudden that a frail spurt betrays the whereabouts of an otherwise secret dwelling-place. In the centre of the disc is the first segment, from which the frontal fringe is extended in the form of an array of keen bristles as a defensive weapon. With the lid at one end and the armed disc at the other the animal enjoys security and comfort, and when unsuspicious the "shoulders" protrude, the head meekly following. The tentacles are serrate and glitter like tinsel, possibly for the fascination of the minute forms of life which the tube-dweller consumes. To enable it to retract and emerge quickly the animal is provided with a series of tufts of bristles on the back and on the ventral surface of the body with a row of toothed "pads," which fulfil the dual office of grapplers and feet.

With what skill and patience does this pectinarian construct its ornate habitation! How artfully does it pick and choose among the tiny shells and grit! With what rare discretion rejects the unfit, and with what satisfaction retains a neat and dainty item of building material! How deftly does it arrange its courses and bonds, cementing each fragment in its place until a perfect cylinder, proportionate in dimensions, uniformly expanding in circumference, smooth within, rugged without, scientifically correct in design, is the result! How apt, too, the frictionless lining! And all this laborious neatness and precision absorbed in the construction of a tenement which has no time! Does the inmate possess any sense of duration? Addison (quoting a French authority) says that it is possible some creatures may think half an hour as long as we do a thousand years! The magnificent mind of the modern biologist regards a million of years as a mere fag-end of time. The industrious worm which has built so choice a home may have enjoyed the sense of comfort and security for a period representing an honourable age, while, according to the standards of man, the home was not worth the building for so short a tenancy.

Do we not see in this astonishing example a highly successful effort of a marine worm to improve on the condition and habits of its barbarous ancestors? Analyse a bulk sample of the building material, and you shall find it not dissimilar from the shell of a mollusc, and the interior film--no doubt a secretion of the animal--is to be safely accepted as analogous to the silky smoothness which molluscs (often of rough and rugged exterior) obtain by nacreous deposit and which finds its culmination in the goldlip mother-of-pearl?

Still higher in the series, so far as the construction of a tenement is concerned, is that known as the SERPULA, a worm which constructs a calcareous tube more or less loosely convoluted and adherent to a shell or stone or coral, or sometimes entwined into a self-supporting colony.

Another worm builds of sand or mud, with a rough casting of fine gravel and shell-grit, a habitation similar in design to that of the serpula, though on a less complete and authoritative model; indeed, it would almost seem that the latter had designed its tenement after the fashion of that of its poor relation--that the one made a study in mud which the other reproduced in carbonate of lime. But the most curious fact is that a true mollusc (VERMETUS) so far departs from the fashion prevalent in the molluscan world of building a spiral shell, that after beginning one in proper spiral mode it elongates itself in vermiform manner and forms an irregular serpuloid tube on the surface of larger shells or stones just as the SERPULA does; so that without examination of the animal one may easily be mistaken for the other.

What a contrast is here--on the one hand a lowly worm learning to build a solid if rude shelly covering for its tender body, on the other a relative of the elegant, many-whorled TURRITELLA forgetting its high station and degenerating to the likeness of a worm. No doubt it is really a case of degeneration from the acquirement of fixed habits, just as when a lively young crustacean larva gives up its free independent life and glues its head to a stone--what happens? Why, he becomes a mere barnacle instead of a spritely shrimp as he might have been! Let mankind take note and beware.

Another group of worm-like or snaky creatures common on a coral-reef are the sea-cucumbers or beche-de-mer. In my experience the most singular branch of the family is at once the longest and thinnest, for it resembles a snake so closely that at first sight the observer subconsciously assumes an attitude of hostility. There seem to be two varieties of the species. One is much more ruddy in appearance than the other, and its body is the smoother; but they are much alike in physique and helplessness. The figure of a sausage-skin four or five and even six feet long, and capable of elongation to almost double, containing muddy water in circulation and one end exhibiting a set of ever-waving tentacles, conveys a not unflattering notion of the animal as it lies coiled among the coral, half hidden with algae. Far too feeble to be offensive, it suffers collapse on alarm--that is to say, if such a violent mental and physical ill can befall an animal of such crude organism. At least, the tentacles are withdrawn, nor will they be protruded until some sense--unlikely to be either sight, hearing, taste, or touch, but probably nervous tension acutely susceptible to vibrations--tells that danger is past. Then the tentacles are shyly exhibited and the agitations of the animal are renewed.

Throughout the length of the body of the more remarkable of the two species of which I may speak on first-hand knowledge are four rows of bosses, closely spaced, which when the animal has dragged its slow length along to the utmost limit diminish into mere wrinkles, and disappear altogether when it is slung across a stick,