FIG. 23.—Primitive band or germ of a Sphinx moth, with the segments indicated, and their rudimentary appendages: _c_, upper lip; _at_, antennæ; _md_, mandibles; _mx_, _mx′_, first and second maxillæ; _l_, _l′_, _l″_, legs; _al_, abdominal legs.—After Kowalevsky. ] Graber also calls attention to the fact that this insect limb differs in one important respect from that of land vertebrates. The leverage system in the last is divided at the end into five parallel divisions or digits. In arthropods, on the contrary, all the joints succeed one another in a linear series. In insects, as well as in other arthropods, modifications of the limbs usually take the form of a simple reduction in the number of segments. Thus while the normal number of tarsal joints is five, we have trimerous and dimerous Coleoptera, and in certain Scarabæidæ the anterior tarsi are lost. Savigny was the first, in 1816, in his great work, “Théorie des organes de la bouche des Crustacés et des Insectes,” to demonstrate that not only were the buccal appendages of biting insects homologous with those of bugs, moths, flies, etc., but that they were homologous with the thoracic legs, and that thus a unity of structure prevails throughout the appendages of the body of all arthropods. Oken also observed that “the maxillæ are only repeated feet.” What was modestly put forth as a theory by the French morphologist has been abundantly proved by the embryology of insects of different orders to be a fact. As shown in Fig. 23 the antennæ and buccal appendages arise as paired tubercles exactly as the thoracic legs. The abdominal region also bears similar embryonic or temporary limbs, all of which in those insects without an ovipositor disappear, except the cercopoda, after birth. LITERATURE ON THE EXTERNAL ANATOMY General =Swammerdam, Johann.= Biblia naturæ. (In Dutch, German, and English.) 1737–1738, fol., London, 1758, Pls. =Réaumur, Réné Antoine Ferchault, de.= Mémoires pour servir à l’histoire des insectes. i-iv, 4º, Paris, 1734–1742. =Lyonet, Pieter.= Traité anatomique de la chenille, qui ronge le bois de saule, etc. 4º, pp. xxii, 616. À la Haye, 1732. Tab. 18. —— Recherches sur l’anatomie et les metamorphoses de differentes espèces d’insectes. Ouvrage posthume, publié par M. W. de Haan. pp. 580, tab. 54, 1832. =Latreille, Pierre André.= Des rapports généraux de l’organization extérieure des animaux invertébres articulés, et comparaison des Annelides avec les Myriapodes. (Mémoires du Mus. d’Hist. Nat., 1820, vi, pp. 116–144.) —— De quelques appendices particuliers du thorax de divers insectes. (Mémoires du Mus. d’Hist. Nat., 1821, vii, pp. 1–21).