The first feature we notice in these creatures is the way in which their bodies and limbs are divided into rings or joints. This fact tells us that they belong to that great division of animals called "Articulates," of which crabs, lobsters, spiders, centipedes, and insects are examples. The celebrated Linnæus called them _all_ insects, because their bodies are in this way cut into divisions.[5] But this arrangement has since been abandoned. However, they are all built upon this simple plan, their bodies being like a series of rings, to which are attached paired appendages or limbs, also composed of rings, some longer and some shorter. Now, there must be something very fitting and appropriate in this arrangement, for the creatures that are thus built up are far more numerous than any other group of animals. They must be particularly well qualified to fight the battle of life; for like a victorious army they have taken the world by storm, and still remain in possession. We find them everywhere--in seas, rivers, and lakes; in fields and forests; in the soil, and in all sorts of nooks and crannies; in the air, and even upon or inside the bodies of other animals. Some of them, such as ants, bees, and wasps, show an intelligence that is simply marvellous, and have acquired social habits which excite our admiration. [5] Lat. _in_, into, and _secta_, cut. Articulate animals are a very ancient race, as well as a flourishing one, for the oldest rocks containing undoubted fossils--namely, certain slates found in Wales and the Lake District--tell us of a time when shallow seas swarmed with little articulate animals known as _trilobites_. They were in appearance something like wood-lice of the present day; and the record of the rocks tells us plainly that creatures built upon this plan have flourished ever since. We mention this because they are related to the king-crabs of the present day, and therefore to the huge old-fashioned sea-scorpions we are now considering. [Illustration: Fig. 1.--_Pterygotus anglicus._ (After Woodward.) 1. Upper side. 2. Under side.]