Fig. 5 is a section of the same spider. The mouth is at _a b_, just under and behind the mandibles, and between the maxillæ. It has an upper, _a_, and under lip, _b_, each lined with a horny plate, in the middle of which runs a groove. When the lips are closed, the two grooves form a tube, which leads to the œsophagus, _c_, and so into the stomach. At the end of the œsophagus is the sucking-stomach. This consists of a flattened tube, to the top of which is attached a muscle, _d_, connected with the groove in the back; and to the bottom, muscles, _f_, attached to a tough diaphragm spreading across the thorax, and fastened between the legs on each side at _g g_. When these muscles contract, the top and bottom of the sucking-stomach are drawn apart, and whatever is in the œsophagus sucked in. By this pumping motion the spider is supposed to take liquid food from the mouth, and drive it backward into the abdomen. Just behind the sucking-stomach, the intestine gives off two branches, _e e_, which extend forward around the stomach muscle, and meet over the mouth. Each of these branches gives off on the outer side four smaller branches, _m m m m_, which extend downward,—one in front of each leg,—and unite on the under side of the thorax. [Illustration: Fig. 5. Section of a spider to show the arrangement of the internal organs: _a_, _b_, upper and under lips of the mouth; _c_, _c_, the œsophagus; _d_, _f_, upper and under muscles of the sucking-stomach; _e_, stomach; _g_, _g_, ligaments attached to diaphragm under the stomach; _J_, lower nervous ganglion; _k_, upper ganglion; _l_, _l_, nerves to the legs and palpi; _m_, branches of the stomach; _n_, poison-gland; _o_, intestine; _p_, heart; _R_, air-sac; _S_, ovary; _t_, air-tube; _u_, spinning-glands. ] The intestine, _o_, continues backward through the abdomen to the anus, in the little knob behind the spinnerete. The brown mass which surrounds the intestine, and fills the abdomen above it, is supposed to be a secreting-organ discharging into the intestine at several points. HEART. Over the intestine, and parallel with it, is the heart, _p_, a muscular tube, with openings along the sides to receive the blood, and branches through which it flows to different parts of the body. The greater part of the blood enters at the front of the heart, and passes backward into the abdomen, or forward into the thorax. BREATHING-ORGANS. In the front of the abdomen are the principal breathing-organs,—a pair of sacs, R, containing a number of thin plates, through which the blood passes on its way to the heart. Besides these, there is a pair of branching air-tubes, _t_, opening near the spinnerets. NERVOUS SYSTEM.