A histological study of the poison glands of the toad demonstrated that one of the components of their secretion is adrenalin or adrenalin precursor substances. The poison glands are arranged in aggregates of two or three making up the warts on the skin. Larger aggregates of poison glands on the head are the parotoid glands. Each poison gland is a large vesicle, deep in the corium of the skin, and opening through a pore in the skin by way of a conical duct. The glandular epithelium of the poison gland is a flat acellular layer of cytoplasm containing a large number of flattened nuclei. Forcibly discharged glands disintegrate, are resorbed, and are replaced by new glands regenerated from the Malpighian layer of the epidermis.