ANIMAL, a term applied to the great primary divisions of the ani mal world. The sub-kingdoms are also named " morphological types," and this latter term serves to indicate their constitution more definitely than the name "sub-kingdom." As an example of the manner in which a "sub-kingdom" of animals is constituted, we may select that of the Annulosa or Articulata, a group of animals which was clearly defined by Cuvier himself, and which has remained since his day, with few alterations, as one of the most distinctive groups of the animal creation. A lobster may be selected as a typical example of this group. In the detailed examination of this animal, we may note that the jointed nature of the tail is perceptible in the fore part of the body, not withstanding that the latter region consists apparently of a single piece. A further examination of the lobster's body would reveal the fact that each joint and its append ages—the latter being " paired"—agrees in essential or fundamental structure with every other joint of the body. The investigation of the plan of structure of the lobster's frame would show a very typical arrangement of parts. The heart lies dorsally, or on the back. The digestive system occupies a median position; and the nervous system lies ven trally, or on the floor of the body. The nerve-axis of the lobster further consists, typ ically, of 'a double chain of nervous masses (or ganglia) united by nervous cords, and from which branches proceed to the various parts of the body. The ideas we may gain regarding the general type of structure of the lobster's body, or plan on which that body is built up, may be thus summarized: (1.) The body is jointed: (2) the joints and their appendages are fundamentally similar or homologous; (3) the heart lies dorsally, the nervous system ventrally, while the digestive system occupies the median position; (4) the appendages are in pairs. Now, if we examine the body of any insect, we shall find
it to essentially resemble that of the lobster in the general arrangement of its parts. The body of a spider or a scorpion exhibits a similar disposition of organs to that of the lobster, and shows a fundamentally similar structure beneath variations in appearance and form; and a centipede's body would be found to be also constructed on the lobster type. The barnacles, water-fleas, crabs, and a whole host of animals more or less nearly allied to the lobster, and belonging to the lobster's class (that of the Crustacea), exhibit a near relationship with the typical animal; while worms generally (leeches, earth worms, etc.,) would present a fundamental similarity in their characters to those described as existing in the lobster. We thus discover uniformity of type beneath variations in form and appearance, and it is exactly this uniformity or broad structural likeness between apparently different animals which enables us to group them together to form " sub kingdoms' or " types." A sub-kingdom or type of animals may therefore be defined as consisting of a number of animals whose bodies are constructed on the same fundamental plan. Lobsters, crabs, barnacles, etc., insects, spiders, scorpions, centipedes, and worms thus form the "sub-kingdom" Annulosa, on account of their agreement in fun damental structure, and in the essential characters just described as being typically exhibited by the lobster. The animal world is thus divided into five or six sub-king doms. Between some of these groups recent research—altogether unfavorable to the con struction of defined sub-kingdoms or types—has demonstrated connecting links to exist, But by the great majority of zoologists, the following divisions arc recognized: I. PnorozoA—Ex. : Sponges, infusoria, anicebm, and other animalcular forms.