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front portion of this tube arise several large tubular rings or "hearts" which are contractile and serve to keep the blood circulating. They lead to a ventral vessel below the food tube (Fig. 74). The blood is red, but the coloring matter is in the liquid, not in the blood cells.

Nervous System.—Between the ventral blood vessels is a nerve cord composed of two strands (see Fig. 75). There is a slight swelling, or ganglion, on each strand, in each segment (Fig. 75). The strands separate near the front end of the worm, and a branch goes up each side of the gullet and enters the two pear-shaped cerebral ganglia, or "brain" (Fig. 75).

Fig. 75.—Ganglia Near Mouth and part of nerve chain of earthworm.

Food.—The earthworm eats earth containing organic matter, the inorganic part passing through the vent in the form of circular casts found in the morning at the top of the earthworm's hole. What else does it eat?

The earth worm needs no teeth, as it excretes through the mouth an alkaline fluid which softens and partly digests the food before it is eaten. When this fluid is poured out upon a green leaf, the leaf at once turns brown. The starch in the leaf is also acted upon. The snout aids in pushing the food into the mouth.

Kidneys.—Since oxidation is occurring in its tissues, and impurities are forming, there must be some way of removing impurities from the tissues. The earthworm does not possess one-pair organs like the kidneys of higher animals to serve this purpose, but it has numerous pairs of small tubular organs called nephridia which serve the purpose. Each one is simply a tube with several coils (Fig. 76). There is a pair on the floor of each segment