The skin of earthworms is kept very moist because of the secretion of mucus from its epidermis and also it possesses excretory pores that release body fluids. These body fluids mixed with plasma act as respiratory pigments. Moist skin helps in picking up oxygen from the air thus playing an important role in the earthworm respiratory system. Oxygen diffuses in and Carbon dioxide diffuses out of the moist skin to complete the process of respiration in earthworms.