The terms joint and articulation, as used here, have a technical meaning. They refer not only to the hinge or place of union of two parts, but also to the parts themselves. Thus, the parts of an insect's legs, as well as the surfaces of union, are styled joints or articulations. All apiarists who have examined carefully the structure of a bee, will at once pronounce it an Articulate. Not only is its body, even from head to sting, composed of joints, but by close inspection we find the legs, the antennæ, and even the mouth-parts, likewise, jointed. In this branch, too, we place the Crustacea--which includes the rollicking cray-fish or lobster, so indifferent as to whether he moves forward, backward or sidewise, the shorter crab, the sow-bug, lively and plump, even in its dark, damp home under old boards, etc., and the barnacles, which fasten to the bottom of ships, so that vessels are often freighted with life within and without. The worms, too, are Articulates, though in some of these, as the leech, the joints are very obscure. The bee, then, which gives us food, is related to the dreaded tape-worm with its hundred of joints, which, mayhaps, robs us of the same food after we have eaten it, and the terrible pork-worm or trichina, which may consume the very muscles we have developed in caring for our pets of the apiary. The body-rings of Articulates form a skeleton, firm as in the bee and lobster, or more or less soft as in the worms. This skeleton, unlike that of Vertebrates or back-bone animals, to which we belong, is outside, and thus serves to protect the inner, softer parts, as well as to give them attachment, and to give strength and solidity to the animal. This ring-structure, so beautifully marked in our golden-banded Italians, usually makes it easy to separate, at sight, animals of this branch from the Vertebrates, with their usually bony skeleton; from the less active Molluscan branch, with their soft, sack-like bodies, familiar to us in the snail, the clam, the oyster, and the wonderful cuttle-fish--the devil-fish of Victor Hugo--with its long, clammy arms, strange ink-bag and often prodigious size; from the Radiate branch, with its elegant star-fish, delicate but gaudy jelly fish, and coral animals, the tiny architects of islands and even continents and from the lowest, simplest. Protozoan branch, which includes animals so minute that we owe our very knowledge of them to the microscope, so simple that they have been regarded as the apron-strings which tie plants to animals. [Illustration: Fig. 1. _A Trachea magnified._] THE CLASS OF THE HONEY-BEE.