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This illustration shows a representation of the circulation of the blood, in its essential features. The arrows indicate the course of the blood. a, arteries; aur., auricle or receiving portion of the heart; d, digestive tract; c. d., capillaries of the digestive tract; c.r., capillaries of the respiratory organs; c.s., capillaries of the system; va., valves; ve, veins; vt, ventricle.

Nephridium

This illustration shows a representation of the circulation of the blood, in its essential features.…