Respiration takes place through the skin in Leech. Dense, network to tiny blood vessels called Capillaries, containing haemocoel fluid extend, in between the cells of the epidermis. The exchange of respiratory gases takes place by diffusion. Oxygen dissolved in water diffuses through the skin, into haemocoel fluid, while Carbon dioxide, diffuses out. The skin is kept moist and slimy, due to the secretion of mucus, which prevents the skin from drying.
