My children had learnt something about the two great divisions of animals, those which belong to the great Backboned Family and those which have no backbone. It is of the latter that we shall speak today. You know that a fish has a backbone, and that it is beautifully formed, for you have often seen it; but perhaps you have not noticed that a lobster, though called one of the shell-fish, is quite unlike the true Fishes: its skeleton is not inside, but outside; there are no bones within, but all the soft parts are inside, and the hard parts outside; while the body of a fish is formed on just the opposite plan. The fish is called a _Vertebrate_ animal, because it has a backbone, made up of numbers of separate bones called vertebras. Some of us know that this word comes from the Latin, and means _that which turns_, because these many small bones are so beautifully jointed together as to be all perfectly moveable, so that the long bone which they form is very flexible. Some snakes have more than three hundred of these vertebræ, and you know how they can coil and twist their glittering length. The marks of a Vertebrate animal are very easy to remember. It must have this wonderfully jointed backbone, and also what is called the skeleton, which is a framework of bone. A spinal cord (from which this division of animals is sometimes called the "Chordate"). Four limbs, and red blood. In these respects all the animals which belong to this division are alike, though in general appearance they may be as unlike each other as a horse is unlike a bird, or a crocodile unlike a herring. Few things in nature are more wonderful than the way in which this Vertebrate plan has been fitted to animals differing from each other in all other respects. Now let us look at the marks of an Invertebrate or Inchordate animal. It has _no backbone_, and instead of a bony framework _within_, to support the soft parts of its body, it generally has a hard shell, or thickened skin _outside_, to protect the softer inner parts. It has _no red blood_. Now, just as plants have been arranged in different classes, so animals are classified according to the various plans upon which they have been formed. So, besides the two great divisions of the Vertebrates and the Invertebrates, the latter have been classed as-- (a) _Radiata_, or Rayed Animals--those whose parts all radiate from a common centre--such as the starfish, red-coral, sea-anemone. (b) _Mollusca_, or Soft-bodied Animals, protected by shells--such as snails, oysters, limpets. (The members of this family are numerous indeed). (c) _Annulosa_, or Ringed Animals--those whose bodies are composed of many parts, jointed together--such as crabs, spiders, bees, ants, centipedes, shrimps, and many more; for this great family has relations among all the insect tribes.