Digestive System

The earthworm's alimentary canal runs as a single straight tube from the mouth to the anus, so digestion proceeds through clearly zoned regions rather than looping organs. Ingested soil first enters the buccal cavity (occupying the first two segments), then the thick, muscular pharynx (segments 3-4), which is surrounded by pharyngeal glands that secrete digestive fluid. A narrow oesophagus in segment 5 leads into a muscular gizzard in segment 6, whose job is purely mechanical - grinding the swallowed soil particles and decaying leaves. From segment 7 onward, the long intestine carries out chemical digestion and absorption; its dorsal wall is folded inward as the typhlosole, a structure that carries blood vessels and greatly increases the surface area available for absorbing digested nutrients. The undigested soil, minerals and organic residue finally leave through the anus as w …