As regards the evolution of limbs of terrestrial arthropods, we have the following stages: 1, the soft unjointed limbs of Tardigrades, ending in two claws, and those of Peripatus, and the pseudo- or prop-legs of certain dipterous larvæ; 2, finally the evolution of the long, solid, jointed limbs of Pauropus and other primitive myriopods, the legs forming solid, firm supports elevating the body, and enabling the insect to drag itself over the ground or to walk or run. When the body is elongated and many-segmented, the legs are necessarily numerous; but when it is short, the legs become few in number, _i.e._ six, in the hexapodous young of myriopods and in insects, or eight in Arachnida. Whenever the legs are used for walking, _i.e._ to raise and support the body, they end in a solid point or in a pair of forceps or claws. On the other hand, as in phyllopods, where the legs are used mainly for swimming, they are unarmed and are soft and membranous, or, as in the limbs of the nauplius or zoëa stage of crustaceans, end in a simple soft point, which often bears tactile setæ. The tarsal joints are more numerous in order to give greater flexibility to the limb in seizing and grasping objects, both to drag the body forwards and to support it. Unlike those of the Crustacea, the limbs of insects are not primitively biramose, but single, the three-lobed first maxillæ, and secondarily bilobed second maxillæ being the result of adaptation. Embryology on the whole proves the truth of this assumption; the maxillæ of both pairs are at first single buds, afterwards becoming lobed. All the appendages of the body, including the ovipositor or sting, are modified limbs, as shown by their embryological development. It is noticeable that in the crab, where the body is raised by the limbs above the bottom, it is much shorter and more cephalized than in the shrimps. Also in the simply walking and running spiders, the hind-body is shorter than in scorpions, while in the running and flying insects, such as the Cicindelidæ, and in the swiftly flying flies and bees, there is a tendency to a shortening of the body, especially of the abdomen. The long body of the dragon-fly is an impediment to flight, but compensated for by the action of the large wings.