The last class of the Articulata, the Arachnida, includes the Spiders, Scorpions, Centipedes, and Millipedes. The Arachnida differ from insects, in having eight or more legs, more than two eyes, no wings, and no head; the Spiders have four pairs of legs, and six, eight, or more, simple eyes, which appear as minute spots on the upper part of the thorax. Spiders nearly all live by preying upon small insects, which they catch in several ways, but by far the most general mode is by constructing a web or net to entangle them; the threads of this web are made of a fluid glutinous substance, which is secreted within the abdomen, and which they project from extremely minute orifices, several of which exist on the point of little projections called "spinnarets," this liquid dries into a solid thread immediately it comes into contact with the air; it is extremely strong, and so fine that several thousand of the single fibres will only make the size of a human hair. The Garden Spider (Epeira diadema) is often called the Geometrical Spider, from the regularity of its web. These Spiders will often place a thread from one spot to another, where it would seem impossible that they could attach it, such as from the branch of a tree to the corner of a house twenty feet or more from the ground; it has never been accurately determined how the Spider does this, and it is the more difficult to observe, as it is always done in the night, but it has been supposed that a fine thread is spun, and that the wind carries it across, when it is strengthened and afterwards made tight. The Spider (Araneæ domestica) that makes "cobwebs" in the corners of rooms, is called the Weaving Spider. Some Spiders are called Hunting Spiders, they do not construct webs, but pounce upon their prey with a leap; the Mygale avicularis of South America is one of this kind; it is said that some grow so large that their feet spread out a foot wide. The Long-legged Spider, often found in our houses, and of which fig. 32 is an exact copy, measures 3 1/2 inches, and is the largest species we have. There are also aquatic Spiders, which feed upon insects in the water and dive down for them; their surface being hairy and unctuous, retains sufficient air to bring them up and prevent them being wetted. The eyes of Spiders are different from those of other insects; they appear as simple, shining spots, or "ocelli," and not compound eyes, having a great many "ocelli" compounded into one. These "ocelli" are arranged in a group of eight or more, and placed on the upper part of the thorax, for Spiders have no head, although generally represented with one. The eggs of Spiders are generally deposited in some sheltered place, fastened together and partly covered with a net-work of a sort of yellow silk, very much resembling the cocoon of the Silkworm. The Scorpion, so terrible in appearance, and in its sting so deadly, and which is sometimes a foot in length, belongs to this order. It has