which, inside, is a muscle that moves the sucking apparatus by which food is drawn into the mouth. At the sides of the thoracic part are four pairs of legs, and on the head part are a pair of palpi and a pair of mandibles. The legs have seven joints: (1) the coxa, the thick basal joint, having little motion; (2) the trochanter, a short joint moving very freely on the end of the coxa; (3) the femur, the largest joint of the leg, moving with the trochanter in all directions; (4) the patella, moving up and down on the end of the femur; (5) the tibia, joined closely to the patella and moving with it up and down; (6) the metatarsus; and (7) the tarsus, moving together on the end of the tibia. The palpi are like small legs and have one less joint than the walking legs. The mandibles are close together at the front of the head (fig. 2). They are two-jointed, the basal joint stout and the end joint or claw slender and sharp-pointed. The claw has near its point a small hole, which is the outlet of the poison gland. The poison kills or disables the insects which are captured by the spider. Its effect on the human skin varies in different persons; sometimes it has no effect at all; oftener it causes some soreness and itching like the stings of mosquitoes and bees, and cases have been known in which it caused serious inflammation which lasted a long time. Spiders seldom bite, and only in defense, the bites so commonly charged to them being often the work of other animals.

Fig. 1. Diagram of the under side of a spider, with the legs removed except one. Fig. 2. Front of head, showing the eyes and mandibles.

On the front of the head are the eyes, usually eight in number, differing in size and arrangement according to the kind of spider. The sight of spiders is distinct for only short distances. Spiders of middle size can see each other, and the insects which they eat, at a distance of four or five inches, but beyond that do not seem to see anything clearly. At the ends of the feet are two claws, curved and with teeth along the inner edge, and in many spiders there is a third shorter claw between them (fig. 212). The claws are sometimes surrounded by a brush of flattened hairs (figs. 104, 114). The basal joints of the palpi are flattened and have their inner edges extended forward so that they can be used as jaws to press or chew the food. These are called the maxillæ. Between the maxillæ is a small piece called the labium, and between the legs is a larger oval piece called the sternum.

The hinder half of the body, the abdomen, is connected with the cephalothorax by a narrow stem (fig. 1). It has at the hinder end the spinnerets, three pairs of appendages having at their ends a great number of microscopic tubes through which the thread is drawn out. When not in use the spinnerets are folded together, so that the smaller inner pair are concealed.

The thread of spiders resembles that spun by caterpillars in making their cocoons, and can be manufactured in the same way into silk cloth. The spider's thread is composed of a great number of finer threads passing from the body through separate tubes and uniting into one before they have time to dry. This can be seen by examining the attachments of spiders' threads to glass. All the spinning tubes are not alike, but on certain parts of the spinnerets are larger or differently shaped tubes, and these are the outlets of glands of different kinds in the spider's abdomen, and are used in making different kinds of threads for certain parts of the webs, nests, or cocoons.

In front of the spinnerets on the under side is a small opening to the tracheæ, or air-tubes (fig. 1). At the front of the abdomen on the under side is a transverse fold of the skin, at the ends of which are the openings of the air-sacs or lungs, and between them the opening of the reproductive organs (fig. 1). The latter is covered in females by an apparatus, sometimes large and complicated, called the epigynum. Its presence shows that the female is full grown. Young spiders do not have it. Male spiders have the ends of the palpi enlarged, and under the terminal joint what is known as the palpal organ, sometimes very complicated in shape. The presence of these organs shows that the male is full grown. Young males that have nearly reached maturity have the ends of the palpi simply enlarged. Male spiders almost always have the body smaller and the legs longer than females of the same species.

The colors of spiders are partly in the skin itself and partly in the hairs and scales that cover it. Almost all spiders are covered with hair of some kind, but in some species it is so fine and short that it has little effect on the color. In others the skin is entirely covered with hairs of various lengths and sometimes with scales somewhat like those of butterflies, flattened and feathered or toothed on the edges. The colors of spiders are very varied, and in many species, especially of the jumping spiders, as brilliant as those of butterflies. The most common colors are grays and browns, resembling the ground or plants and stones among which the spiders live. Sometimes the color is uniform all over the body, except that it is a little darker toward the head and the ends of the feet. The most common marking is a spot on the front of the abdomen over the spider's heart, sometimes merely a translucent part of the skin and sometimes a definite color spot darker in the middle and outlined with a lighter shade or white. The hinder half of the abdomen is often marked with several pairs of spots, becoming smaller toward the end, and these spots may be united into a pair of stripes or a more complicated pattern. (See figures.) The legs are often marked with rings of color, almost always at the ends of the joints. Besides these common markings there are in some spiders strong contrasts of color, such as bright red or yellow spots on a black ground. In the males, especially among the Attidæ, there are often shining scales that reflect different colors in a bright light, and tufts of black or white hairs about the head and front legs.

Spiders live in all kinds of places. Certain species are attached to houses and seldom found far from them, and many of these occur over a large part of the world. The light webs in the corners of rooms are