CENTIPEDE, an animal with a distinct head, one pair of feelers (antennae) and a long segmented body, each typical seg ment' of which is provided with a single pair of walking legs. The Centipedes form in the phylum Arthropoda (q.v.), the dis tinct class Chilopoda in which well defined subdivisions may be made as follows:— First Sub-class Epimorpha, in which the young leave the egg with the full number of body segments and walking legs.
This sub-class comprises two orders : (i.) Geophilomorpha (contain ing ten families) with Geophilus as the typical genus, and (ii.) Scolopendromorpha (con taining two families), Scolopen dra being the typical genus.
Second Sub-class Anamorpha, in which the young leave the egg with 7 pairs of legs. Afterwards there are periods of growth each of which is followed by a change of skin, resulting in an increase in the number of pairs of limbs until the adult condition is reached. In this sub-class, also, there are two orders : (i.) Lithobiomorpha (containing three families).
Lithobius is the typical genus, and (ii.) Scutigeromorpha (consisting of one family), with the genus Scutigera as type.
In considering the anatomy of the centipedes, we picture a hypothetical ancestor without a distinct head but provided in front of the mouth with a single undivided projecting lobe, the prostomium (seen to-day in the earthworm and its allies) ; the body otherwise consisted of a long series of similar ring-like seg ments or somites, each provided externally with a single pair of limbs and internally with its own share of the gut, and of the muscular, nervous, excretory, respiratory, blood-vascular and re productive systems.
In the modern centipedes the head is distinct and may be re garded as a concentration and fusion of a pre-oral lobe (prosto mium), one pre-antennal somite, one antennal somite, one inter calary somite and three somites bearing masticatory appendages (mandibles, first maxillae, second maxillae).
The segment immediately behind the head bears the poison claws or maxillipedes and this is followed by a variable number of segments, each bearing a single pair of limbs.
The head, body and limbs are invested with cuticle which remains flexible wherever movement of the parts is necessary and elsewhere is thickened by a deposition of horny chitin. In a typical limb-bearing segment consisting of a roof, a floor and side walls, the cuticle covering these is reinforced to form definite protecting and support ing plates or sclerites, differently arranged in different forms. Ex cept at the joints the cuticle of the limbs is similarly hardened.
The last three segments of the body (called pre-genital, genital and anal segments) are without walking legs.
Eyes occur in most Lithobio morpha, all Scutigeromorpha and in all Scolopendromorpha except one family (Cryptopidae). They are absent in Geophilomorpha. A simple eye (ocellus) or a group of separate ocelli is usual but in Scutigeromorpha the external lenses of the group of units fuse into a single facetted lens.
On each side of the head in Anamorpha a sense organ (organ of Tomosvary) of unknown func tion occurs; it consists of a group of cells below the chitin associ ated with an external hollow near the antenna. The frontal organ of Lithobius and Scolopendra consists of a group of deep-seated nerve cells behind each eye—its use is unknown.
The digestive tube is simple ; it receives, in front, the products of the salivary glands and, further back, those of the excretory (Malpighian) tubules. Its opening is in the anal segment.
The main nerve-cord lies below the gut and ends in front in a nerve mass (the sub-oesophageal ganglion) united with the supra oesophageal ganglion or "brain," which lies above the front of the gut, by a pair of stout nerve cords.
Breathing is by air tubes or tracheae which open at the sides of the body except in the Scutigeromorpha in which the open ings are in the middle line of the back.
The heart, which lies above the gut, is a simple tube and the blood-circulation is in the direc tion usual in invertebrates—for ward dorsally and backwards ventrally.
The reproductive system, which lies above the gut, varies in different centipedes. In the male the number of testes ranges from one to twenty-four. In the adult female the ovary is always unpaired. The reproductive sys tem opens in the genital segment.
From any detailed considera tion of anatomy it is clear that the centipede's nearest relatives are insects and that the relation ship with millipedes is much more distant.
Owing to the retiring habits of centipedes comparatively little is known about their reproduction. Although the satisfactory obser vation of copulation has never been recorded, on anatomical grounds it is believed to take place. In the Anamorpha the female after laying each egg car ries it about between the special ised claws at the hinder end of her body and eventually, when it has been smeared with a secretion or earth, or both, lays it down where its covering is sufficient protection against enemies.
The eggs of Epimorpha are laid in an open nest and the female guards them faithfully until hatching takes place.
The egg is rich in yolk; this serves as food for the develop ing centipede which grows from a special area in the lower part of the egg. An examination of the developing animal when the proc ess has been some time in prog ress may reveal the beginnings of the various head segments and of the walking limbs. When the animal at length leaves the egg its form varies as already indi cated, according to the order to which it belongs.
Centipedes as a class have a world-wide distribution.
Fossil centipedes occur in am ber of Oligocene age but all older remains tentatively referred to the class Chilopoda are proble matical. The least generalised centipedes (the Lithobiomor pha) are the shortest and we are led to conclude that in the evolu tion of the race the principle of contraction has been at work gradually reducing the number and similarity of the segments of the centipede's body.
Many Geophilomorpha have the power to give light, but as these animals are blind the property is perhaps accidental. The light is produced by the simultaneous discharge upon the lower surface of the body of two kinds of glands, which occur in the floor of the body segments. When the two fluids mix outside the body a light is produced.
When the gardener hunting for slugs at night with a lantern sees Lithobius carrying off a small slug and shaking it as a terrier shakes a rat he rightly assumes that the centipede is his friend; but Lithobius may kill and eat beneficial insects as well. Geophilo morpha are certainly carnivorous at times, but one species (Haplophilus subterraneus) has been known to damage growing celery, lettuce and onions, and other species are likely to be similarly injurious at times.
The painful bite of large centipedes may on occasion cause danger to life. "The part bitten should be bathed in a solution of ammonia—about i in 5" (Hirst). Pseudo-parasitism in Man may be due to accidental invasion of the ear or nasal pasages and adjacent sinuses by Chilopoda ; or to swallowing them either accidentally or in a state of impaired men tality.
Brief mention of centipedes is made by early writers (Aristotle, Pliny, Aelian). Oviedo, the companion of Columbus, describes the occurrence of centipedes in the island of St. Domingo, where he was supervisor of gold smeltings, and mentions the bright light emitted by some of them.
The literature in English is very scattered—most of the best modern accounts are in German.
See F. G. Sinclair, "Myriapods" in Cambridge Natural History, vol. 5 (1895), useful information in accessible form; K. W. Verhoeff, "Chilopoda" in Bronn's Klassen and Ordnungen des Tier-Reichs; K. Graf v. Attems, "Chilopoda" in Handbuch der Zoolngie, vol. 4 (1q26) ; for luminosity in Centipedes, S. G. & H. K. Brade-Birks, "Luminous Chilopoda" in Annals and Magazine of Natural History (1920) ; fossil Centipedes: Zittel's Text Book of Palaeontology (edit. Eastman, 1013).
(S. G. B.-B.)