Popular Science Monthly/Volume 9/September 1876/Myriapods
|←The Revived Theory of Phlogiston||Popular Science Monthly Volume 9 September 1876 (1876)
PLEASE, sir, here's one of them nasty mischiefull many-legs as I told you pisened the melon-bed so as we never got nothink off of 'em. Nobody can't say as they wasn't took care of, for I was a waterin' and a waterin' on 'em mornin', noon, and night, all along the droughty summer. It stands reasonable like to natur' as water-melons should take a sight o' water; 'twasn't my overdoin' on 'em with m'isture as rotted the roots off; 'twas these here plaguey varmint!"
Having delivered this oration, and proved to his own entire satisfaction "as how he was right all along, and master was mistook" about poor Curcurbita citrullus having been drenched to death with icy pump-water, the obstinate old gardener deposited his writhing scape-goat on the study-table, and retired triumphant to the coach-house, where he whistled loud pæans of victory to the Bramahs and Cochins of the stable-yard.
What yellow-brown Myriapod is this? His flexible body, which he is tying into all manner of knots, is composed of no fewer than eighty-one distinct segments, to say nothing of the odd one at the end of the tail, and the five which have coalesced to form the head. If we count these five fused segments as one (as we do the four which Prof. Huxley tells us combine together to make up our own human brain-boxes), then his body is made up of eighty-three somites, of which the cephalic, the anterior-thoracic, which bears that terrible pair of hooked maxillipedes, and the anal, are the only three presenting any marked differences from each other, and from the eighty others which are as "strictly uniform" as the helmets of the metropolitan police.
How the fellow shuns the light! Does his conscience trouble him? Does he feel himself guilty of "pisenin'" the melons, that he wriggles so uneasily until he succeeds in burying himself out of sight in the silk tassel of the pen-wiper? A burrowing troglodyte by nature, I suspect, and on closer examination he proves to be such—Geophilus subterraneus (underground earth-lover), of the family Geophilidœ, of the subdivision Chilopoda (foot-feeders), of the order Myriapoda, of the class Articulata, according to Newport.
He has no eyes; he doesn't want any; he passes his life in the dark, underground, tearing up old shreds of farmyard manure and vegetable matter, always preferring scavengers' work when he can get it, and doing good service by eating up the helpless, soft, succulent larvæ of the hosts of insects that prey upon our crops. The sins of the wire-worm have been laid to his charge; his third cousins the Iulidœ do undoubtedly steal our potato "sets," and bore into young peas, or rather into old peas just "splitting" and about to send up young ones; but it seems doubtful if he himself ever attacks fresh or living vegetables; he seems to be one of Nature's many vidangeurs, and, because he is found minding his business and eating up rottenness, he is accused of producing it. As well might we say that our sewer-men produce typhus and cholera. But he has even been charged with having caused the potato-disease! because he was found laboring to remove the affected tubers. Beware, ye brave surgeons who fight with zymotic demons and risk your own lives to lift up stricken humanity, lest ye be arraigned for producing all the long catalogue of human ills that figure in our sanitary statistics!
Our captive has no eyes; he has, however, an "ocellus," a mere pigment-speck behind the base of each of his fifteen-jointed antennæ, and he has the smallest possible threadlet of an optic nerve. I suspect he cannot see, in the ordinary sense, but can distinguish between the light with which he has nothing to do, and the darkness in which he feels his way about with his antennæ when doing his duty like a humble vegetarian jackal, or adjutant.
The Myriapods have been placed at different times in different classes of the animal kingdom. In one famous system we find them under the head of Crustacea; another, in remote times, ranged them with the Hemiptera and Orthoptera as "insects which only undergo a partial metamorphosis." They have slight affinities with both, and even with the Annelids; like the latter, they grow in length by the successive addition of new segments between the penultimate and anal. The lower subdivision, the Chilognatha, by the situation of their reproductive orifices, seem to betray Crustacean relationships; but we remember that, in the first phase of their development, they displayed three pairs of legs only, like the typical hexapod insect. They appear to stand out the strong, well-marked, first link of that long chain which bridges over the mighty gulf which rolls between the creeping worm and the flying insect. The Myriapod is the lowest articulate animal, the Annelid the highest annulose—i. e., according to the old scheme of classification, the latter term has recently been used with a widely-extended signification. Ten years ago the subdivision Chilopoda consisted of four families, including ninety-four genera; and the lower subdivision, Chilognatha, of four families, containing seventy-five genera; a tremendous total of variations of a type; but since then they have been shuffled and cut, and lumped and split, like the German states, till nobody knows which is which.
"An articulation complete in all its mechanical appliances is not produced in the animal kingdom below the Myriapod. A joint is the symbol of organic superiority; it is not an arbitrary symbol; it is a unit in an assemblage of signs which proclaim a newer and higher combination in the arrangements which constitute 'life.' At this limit in the animal series the fluids and the solids of the organism undergo a signal exaltation of standard. The system of the chylaqueous fluid exists no longer in the adult organism, it is present only in the embryonic. It is supplanted by that of the blood proper. Coincidentally with the 'joint' at the frontier of the articulate sub-kingdom there occurs a heart to circulate the blood, fibrine, and with it an order of floating corpuscles more highly organized in the fluids; a wondrous development of the muscular apparatus, striæ in the muscle-cell, a rapid increase in the dimensions of the cephalic ganglia, and in those of the organs of the special senses. It is here in the history of the reproductive system that the diœcious character is first unquestionably assumed. These are noteworthy events in the ascensive march of organic architecture."—(Dr. Williams, Magazine of Natural History, 1854.)
The armor-plates of the cylindrical Iulus are composed of a semicrustaceous hard substance, but in the Scolopendridœ, which our "false wire-worm" closely approaches, the integuments are of a flexible chitinous substance, the back of each segment is covered by a plate, the ventral surface by a somewhat smaller plate, the epimeral portions, as well as the interspaces between the somites, are covered by a loosely-fitting coriaceous membrane of much thinner texture.
The circulating system has been a battle-ground for men with great reputations. The nervous and reproductive systems, and the development day by day from the ovum, have been drawn out with elaborate minuteness by Newport, in "Philosophical Transactions" for 1841 and 1843, but I have not fallen in with a drawing of their tracheary system, which is well worthy of careful study.
The spiracular orifices are not placed as in insects between the segments, but in the side of each, a little below the dorsal plate; they are not minute apertures, nor vertical slits, neither are they furnished with "guards" of setæ, or hairs, to exclude dust and foreign bodies; but they are circular openings, each with a well-defined, hard-looking ring, over which the tough but pliable lateral membrane passes, lining the entrance, which is directed slightly backward, and can be closed by a sphincter-muscle. The tracheæ are very large in the anterior segments, occupying no small portion of their internal cavities, but they decrease in diameter in proportion as the segments recede from the head; possibly there may be need for a more abundant supply of oxygen in the region of the brain, and in the first-formed portions of the body, than in the equally large but more remote additions which are from time to time developed near the caudal extremity.
Let us detach half a dozen pairs of spiracles, with their tracheal appurtenances complete, from the dissected tail-end of Geophilus the much maligned, float them on to a slide, and bring the "two-thirds objective" to bear upon them.
A ladder of shining silver, a very Jacob's ladder, bright and beautiful enough to have been let down from heaven for the feet of angels.
The six uprights and the cross-rungs are all constructed of the same tubular wire rope glistening with a dazzling metallic lustre, and without a flaw anywhere. The tubes are composed of an outer and an inner coat, containing between them the spiral coil, to which they are closely attached; a delicate membrane also connects the turns of the spiral with each other.
|Tracheæ of Geophilus Subterraneous. Magnified 140 diameters.|
It is interesting to compare these animal breathing tubes with their analogues the spiral vessels of the vegetable kingdom; the latter are easily extracted from the young shoots of asparagus, or from the leaves of the hyacinth. The spring-like coil insures a free open passage for the air which rushes in by the spiracular orifices, expiration being effected by the contraction of these elastic channels, by which the effete air is forcibly expelled through the openings by which it originally entered.
The main tracheæ pass down the axes of the blood-channels, floating in the vital fluid, which they revivify with the oxygen which they thus carry to and through the life-stream. We are told that the air-pipe does not terminate where the wiry-looking spiral comes to an end; the latter dwindles away imperceptibly to nothing, but the trachea thence becomes membranous, and, dividing into innumerable branches, which bear to the main trunks the same relations that the capillaries bear to the arteries, penetrates the substance of the muscles, inconceivably fine branches having been traced accompanying the nerves, while the ultimate plexiform extremes of the system aërate immediately the solids. "In all the transparent structures of insects every observer may prove for himself that the blood-currents travel in the same passages as the tracheæ, but this is only the case with the primary and secondary branches, never in the capillary tracheae; the blood-corpuscles of the Myriapod exceed by several times in diameter that of the extreme capillary membranous tracheæ; it is perfectly marvelous to what inconceivable minuteness the air-current is reduced in traveling along these tubes." What a simple and efficient plan, what an economy of space is this arrangement of tube within tube, for aërating the blood in a class of lowly, creeping things of earth that do not attain to the dignity of lungs! There is a saving of time, too, for the blood is made arterial while on its journey, and thus travels direct (without the delay of passing off to special pulmonary organs) to the performance of its functions, removing, replacing, renewing, sustaining, building up, absorbing. Having accomplished these, and become as it were venous, it passes into the intervisceral spaces, and there, receiving an increment of fresh globules, the products of digestion, completes its circuit by returning through distinct valvular openings into the dorsal vessel from which it was first distributed. "Among the Chilognatha," says Siebold, "the Iulidœ are noticeable for the very simple character of their trachean apparatus; their air-canals neither ramify nor anastomose. With the Glomerina the tracheæ are branched, but do not anastomose; but those of the Chilopoda are very ramose, and their large trunks intercommunicate at their origin by longitudinal and transverse anastomoses, so that each stigma can introduce air into the entire trachean system." It was chiefly with the view of drawing attention to this last-mentioned fact (a most striking evidence of design), to this remarkable example of the exquisite adaptation of the creature's construction to the condition of existence ordained for it by the Creator, that I began this bit of simple gossip about Geophilus. In his subterranean career he constantly meets with accidents which link him up in sympathetic association with Brunel and Stephenson, and the Bedouin of the desert. He never bored a practicable highway beneath the bed of Isis, nor made firm the foundations of an iron road across the quaking surface of Chat Moss; neither has he braved the burning sand-blasts of the simoom; yet in his degree he has met with such like critical experiences a hundred times.
One day the roof of his tunnel crashed in upon him, and buried a dozen of his segments, squeezing the very breath out of them; on another day the rain had saturated the rubbish-heap he was toiling in, a score or two of his somites were under water, and he had to "batten down" the stigmata belonging thereto to save those portions of himself from drowning; and yet, again, in the scorching dog-days, a hot wind swept the earth, and a dry and thirsty clod, crumbling away, discharged an avalanche of dust which overwhelmed nine-tenths of him. In each and all of these catastrophes his life would not have been worth ten seconds' purchase, even with his many spiracles, but for the anastomosing branches of his windpipes, the cross-rungs of his air-ladder, which enabled the air received by the unchoked segments to pass in every direction through the whole system. That there is perfectly free communication from any one spiracle to the whole network of air-passages maybe seen by examining the figure which I have given; and if any reader has still a doubt on his mind he may remove it, if he is a dexterous manipulator, by dissecting out the tracheary apparatus of the first chilopodous Myriapod he can lay hands on; and, stopping the orifices of all the spiracles but one, he will find that through that one he may inject the whole labyrinth of air-vessels with carmine.
I observed that a correspondent, J. G. D., in December last, was much surprised at the display of a phosphorescent light by a centipede he had found. Geophilus electricus, a member of the same family, and a near relation of our Subterraneus, must have been the pyrotechnist he chanced upon. "The caustic brown fluid which most Myriapoda when touched emit from a row of orifices, foramina repugnatoria, situated on the sides of the segments of the body, and which exhales an odor like that of chlorine, is secreted by small pyriform glandular follicles situated immediately beneath the skin; it is from glands upon the sides of the body analogous to these that Geophilus electricus emits a luminous liquid."
It would be most interesting to ponder over the three varieties of breathing apparatus mentioned by Siebold, and to note their special adaptations to the life conditions and necessities of the three distinct genera provided with them; and there are other wonders in the ways and mechanism of each and all of them that one longs to dwell upon; but we are not essayists here, only cheerful "gossips" of the wayside, who seek to be merry and wise, accurate, though simple and amusing. We have run to the end of our tether, and must say good-by to Geophilus subterraneus and all the Myriapods.—Science-Gossip.