MYRIAP'ODA (Neo-Lat. nom. pl., from 1111k. loynInrovs, myriopous, having ten thousand feet, from Gk. pilptoi, myrioi, ten thousand + roi3s, pons, foot). A class of arthropods resem bling annelids in their lengthened form, and in the great number of equal, or nearly equal. seg ments of which the body is composed; but in most of their other characters nearly agree ing with insects, among which they were ranked by the earlier naturalists. They differ from insects and all other arthropods. in the fact that the posterior segments of the body hear jointed locomotor appendages. In addition to their affinities with insects, myriapods are worm-like and some of them suggest relations with the sanurans. They have a distinct head, but there is no distinction of the other segments, as in insects, into thorax and abdomen. They have simple or compound eyes; a few are destitute of eyes. They have antennae like those of insects. The mouth is furnished with a complex masticat ing apparatus, in some resembling that of some insects in a larval state, in others similar to that of crustaceans. Respiration is carried on through minute pores or spiracles, placed on each side along the entire length of the body, the air being distributed by innumerable ramifying air-tubes to all parts. In most parts of their internal organization the myriapods resemble insects, although a decided inferiority is exhib ited, particularly in the less perfect concentra tion of the nervous system. The resemblance is greater to insects in their larval than in their perfect state. The body of the myriapods is pro tected by a hard ehitinous covering. The number of segments is various, seldom than 21, although in some of the genera they are con solidated together in pairs, so that each pair, unless closely examined, might be considered as one segment bearing two pairs of feet. The legs of some of the lower kinds, as 'Tullis, are very numerous, and may be regarded as between the bristle-like appendages which serve many annelids as organs of locomotion and the distinctly articulated legs of insects. In the higher myriapods, as Scolopendra, the legs are mueh fewer, and articulated like those of insects. Some of them feed on decayIng organic matter, chiefly vegetable; those of higher organization are carnivorous. The myriapods do not undergo
marked metamorphoses. but the young greatly resemble the adults, although some of them are at first (unite destitute of feet : and, contrary to what takes place in insects, the body becomes more elongated as maturity is approached—the number of segments and of feet increase.
Myriapods are widely distributed, and are rep resented in almost every part of the earth. They flourish in moist and dry. hot and cold climates. Like other widely distributed animals, they show great variation in size and color, ranging front microscopic size to a length of more than six inches. Some of the Julithe and of the tropics are beautifully and brilliantly col ored. Some of the species of Geophilus are phos phorescent. Most myriapods inhabit dark and obscure places. Some of the cave-inhabiting species from Wyandotte and Bradford caves in Indiana are described by Packard as light in color, and those from the latter cave have rudi mentary eyes. The organs of defense throughout the class vary greatly. In the centipedes the large claws, supplied with poison from a gland, are weapons of offense and defense. The milli pedes, on the other hand, rely for defense on an acid secretion from certain glands. Other forms are hairy or bristly. hairiness was the most common mode of defense among fossil myriapods.
A fossil bristled myriapod has been found in America in Paleozoic strata, and two species have been found in the Old Red Sandstone of Scot land. The highest vertebrates in this deposit are fishes, and the highest plants are conifers. The Paleozoic .species, about forty in number, all be long to an extinct order (Arehipolypoda) and most of them were of gigantic size. Later fossil myriapods, contemporaneous with giant fossil Amphihia, occur in the coal measures. One of these forms from Illinois approaches very closely the Julidlc of to-day. Only one species has been found in the chalk layers, but in Ter tiary and recent times plentiful remains have been found. The majority of these belong to the Chilognatha and Chilopoda. They have been found in the gypsum of France, in the brown coal of Germany, and in the Green River formation of North America. Amber has also yielded sev eral species.