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.
The nervous system has a large ganglion, J, in the thorax, from which branches, i, pass to the limbs and abdomen. At the front end two branches extend upward, each side of the œsophagus, to two smaller ganglia, k, from which pass nerves to the mandibles and eyes.
The reproductive organs, S, lie along the under side of the abdomen, and open between the two air-sacs.