somite

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. See metamere.
2. n. A segmental mass of mesoderm in the vertebrate embryo, occurring in pairs along the notochord and developing into muscles and vertebrae.

Century Dictionary and Cyclopedia

1. n. An actual somatome; any one morphological segment of an articulated body, such a body being viewed as composed of a longitudinal series of somites; an arthromere or metamere of an articulate invertebrate or a diarthromere of a vertebrate; such a segment considered with or without the appendages it may possess; in the latter restricted sense, a metamere minus its appendages, or a segment of the soma or trunk without the limbs it may bear. The term sometimes extends to ideal somatomes, or to the metameres of which an organism is theoretically assumed to consist; but it is especially applied to the actual segments of such invertebrates as insects, crustaceans, and worms, whose body-rings are usually evident, though some or other of them may coalesce, as into a cephalothorax, etc. In such cases the primitive or morphological somites are usually recognized and reckoned by their respective pairs of appendages. Separate somites, continued thronghout the body, are evident in the rings of earthworms and other annelids. In arthropods the typical number of somites is supposed to be twenty or twenty-one, numbers often actually recognizable. In insects the head is assumed to have six or seven somites, the thorax has normally three (see prothorax, mesothorax, and metathorax), and the abdomen is supposed to have ten or eleven. Each of these somites is invested and indicated by a body-ring or crust of integument, primitively or typically composed of eight sclerites, which may variously coalesce with one another, or with pieces of another somite, or both. Those sclerites which ordinarily remain distinct, and thus can be identified, take special names, as tergite, pleurite, sternite, scutum, præscutum, etc., epimeron, epipleuron, etc. Appendages of somites are limbs in the broadest sense, nnder whatever modifications; and these modifications are usually greatest at the cephalic and caudal ends of the body, as into eyestalks, antennæ, palpi, mandibles, maxillæ, maxillipeds or gnathopodites, etc., of the head, and stings, claspers, or other anal armature. Intermediate somitic appendages are ordinary legs and wings, as of the thorax of insects, and the pereiopods, pleopods, chelæ, rhipidura, telson, etc., of the thorax and abdomen of crustaceans. In worms such appendages chiefly occur in the form of parapodia (neuropodia and notopodia). See sclerite, and cuts under Amphithoë, Apus, Buthus, Scorpionidæ, Blattidæ, and cockroach.

Wiktionary

1. n. embryology One of the paired masses of mesoderm distributed along the sides of the neural tube that will eventually become dermis, skeletal muscle, or vertebrae.
2. n. anatomy A metamere, one of a series of segments, arranged longitudinally, of which some animals are composed.

GNU Webster's 1913

1. n. (Anat. & Zoöl.) One of the actual or ideal serial segments of which an animal, esp. an articulate or vertebrate, is composed; somatome; metamere.

WordNet 3.0

1. n. one of a series of similar body segments into which some animals are divided longitudinally