ARTICULATA (articulus, a joint,) a pri mary division of the animal kingdom founded by Cuvier,* and characterized by him as follows : " Body jointed externally, corresponding to the divisions of the nervous system internally : a very small brain placed above the oesophagus gives off two filaments which extend along the abdomen and unite together from distance to distance by means of ganglions, which resem ble as many small brains, from which nerves are given off. The muscular system is disposed on the inside of the rings or segments of the body so as to separate and approximate these segments ; when there are articulated mem bers, the muscles of these parts are also placed within the hard parts. The divisibility of the body, and the power which the fragments possess of retaining a kind of independent vitality corresponds to the distribution of the nervous system into as many centres as there are corporeal segments." With respect to the agreement between the number of segments of the body and the ganglions of the nervous sys tem, it must be observed that in the higher crustaceans, arachnidans, and insects, the gan glions, though originally as numerous as the segments, subsequently become concentrated by progressive development into masses which are fewer in number, and that also in some of the lowest annelidans, as the leech-tribe, the ex ternal segments are more numerous than the internal ganglions.
In many of the rnolluscous class two nervous cords proceed backwards from the supraceso pliageal ganglion or brain, and are afterwards brought into communication by ganglionic masses on the ventral aspect of the body ;. but in the Articulata the uniting ganglions are always confined to the mesial line of the body, are perfectly symmetrical in their arrangement, and are accompanied by a symmetrical or bila teral form of the whole body. It is this homo gangliate dispositiondisposition of the nervous system which essentially distinguishes the Articulate from the Molluscous and other divisions of the Animal Kingdom, and it is an infallible guide to the true affinities of the classes possessing it. The Cirripeda present a striking example of this fact : these animals, on account of their inarticulate body enveloped in a fleshy mantle and protected by a multivalve shell, were for a long time classed with the mollusca : but the views of those naturalists who considered that they had closer relations to the Ara culata, although that opinion was founded on a knowledge of their nervous system only, has since been corroborated by every additional fact which has been discovered respecting them. Latreille, in his " Families Naturelles
du Regne Animal," first placed the cirripeds in the Articulate series, but being guided by their adult organization, and supposing that they were deficient in visual organs, and underwent no metamorphosis, he joined them with the an nelidans, to form a division of Articulate ani mals, " Elminthoida," distinct from the " Con dylopeda," which include the insects, arach nidans, and crustaceans, or the Articulata with jointed, feet. The later researches of Mr. I. V. Thompson and Dr. Burmeistert have proved that in the immature state the Cirripeds un dergo repeated metamorphoses or moults ; that they move freely in the water by means of setiferous articulated members, and during this period guide their wanderings by the aid of distinctly developed, though simple eyes.
Besides the cirripeds the higher organized infusoria and intestinal worms have been proposed by some naturalists to be added to the articulate division of Animals : but as they are neither articulated nor possess articulate members, and as their nervous cords are sim ple and not brought into communication by a regular series of ganglions, we prefer to leave the Rotifera and Cmlelmintha with the Entozoa and Echinodermata, as a separate and higher subdivision of Cuvier's Radiata, and thus pre serve the Articulata as a distinct and well de fined subkingdom, characterized by a dispersion of the nervous system in a series of ganglions, symmetrically arranged and brought into com munication by a double nervous cord ; by an articulate or jointed structure of the body or its appendages, by the lateral position and hori zontal movements of the jaws, when these are present, and by the presence of distinct respi ratory organs. The subdivisions of this sub kingdom are not founded on the modifications of any single system, but principally rest on the conditions of the sanguiferous and respira tory organs, in connexion with exterior form, modes of locomotion and generation.