Hirudo medicinalis·Fig. 2. Hirudo medicinalis, the medical leech. A, ventral aspect; the outer annulation does not confer to the inner segments (1–33). B, inner structure. After copulation and transfer of so-called double spermatophores, fertilized eggs are packed together into slime () deriving from the and are deposited on plants. After a period depending on the temperature of the water, the young worms hatch from the eggs and reach maturity within 5–6 months. A, anus; B, ventral nerve cord; BS, last intestinal caecum; C, D, intestinal caeca; DG, dorsal blood vessel; E, = openings of the 17 pairs of ED, rectum; G, genital porus; H, HD, hind gut; HS, posterior ; NE, nephridium; O, ovary; P, penis; PH, pharynx; S, sensory papillae; SD, salivary glands; V, vagina; VS, apical sucker
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