ARTHROPODS

n. pl. A*rth'ro-po?dz. See ARTNROPODA.— Branchiate a. The crustaceans, [L.] ARTHROPOD A (Lat.), n. Bab A$rth-ro*p’o7d-a3, From ép- 8pov, a joint, and mods, a foot. Fr., arthropodes, arthropod a ires. Ger., Arthropoden. Gliederfi ler. Syn.: Articulata(in part). Articulate animals; one of the two primary divisions of the Annulosa, comprising the cla es Crustacea, Arachnid a, Myriapod a, and In’ sect a. The body is composed of a series of segments arranged alon; a longitudinal axis, each occasionally, and_some always, provide with articulated locomotor appendages. Both the body and the appendages are provided with a chitinous exoskeleton; the appendages are hollow, with muscles prolonged into their interior. ‘he nervous system consists of a double chain of ganglia on the ventral surface of the body, united by longitudinal commi ures and traversed anteriorly by the cesophagus. The hæmal system, when differentiated, is dorsal, and consists of a valvular heart communicating with a cir cum visceral cavity. Respiration is effected at the surface, by gills, pulmonary sacs, or tracheæ. Typically, the head is composed of six segments, and never has fewer than four. Bi L, 147.j—A. branchiatn. See CRUSTACEA.—A. hexapod a. e INSECT A.