Every one knows a Spider when he sees one, though not every one can give offhand a definition that shall include the whole Order. Let us endeavour to express their characters in simple terms, keeping in mind the definition of head, thorax, and abdomen in Chapter II. In Spiders the head and thorax are joined together in one unsegmented portion, called the cephalothorax, and this is connected with the abdomen, which is also unsegmented, by a more or less slender stalk or peduncle. So that while Insects have three regions, Spiders have but two. We may express the difference thus: Insects head, thorax abdomen. \---v---/[image] Spider cephalothorax abdomen. The cephalothorax bears six pairs of appendages (Fig. 48A). Taking these in order, there are-- 1. A pair of falces (_an_), representing the antennae of insects. These have a movable claw-like joint at the extremity, perforated so as to convey into a wound the secretion from the poison-glands. 2. A pair of five-jointed pedipalps (_p_), sometimes called maxillary palpi, from the fact that the parts whence they spring correspond to the maxillae of insects (Fig. 21A, _d_). In the female the last joint terminates in a claw; in the male this joint is specially modified for sexual purposes (Fig. 48B). 3. Four pairs of walking legs, of which only the coxae (_c_) are shown in the diagram. The two front legs are often used as organs of touch. Breathing is carried on by chambered air-tubes or lung-sacs, and in all our British Spiders (with the single exception of the native Trap-door Spider, which, by the way, does not make a trap-door) there are also air-tubes resembling those of Insects. The lung-sacs open to the external air by stigmata (_st_) on the abdomen, while the ordinary air-tubes open near the spinnerets (_sp_), the organs employed in the production of the silky threads from which are formed webs, nests, egg-bags, and ropes. By means of these threads, spiders drop from their webs to the ground, construct flying bridges from one point to another, and even in some sort travel through the air. Spiders live upon the juices of their prey, which are drawn up into the stomach by means of a suctorial apparatus at the end of the gullet. The young, when they leave the egg, resemble their parents in all respects but size--that is, they undergo no metamorphosis. The eyes of spiders are simple, and six or eight in number. These vary much in size and relative position, and furnish characters of great importance in classifying species. Those of the Hunting Spiders, which make no web, but pursue or spring upon their prey, are usually arranged in three rows; while those which make webs for the capture of prey have the eyes in a double row. In all cases they are on the front part of the upper surface of the cephalothorax. [Illustration: