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The specialized gland of certain fishes, as well as the granular glands and some mucous glands of many aquatic and terrestrial Amphibia. The poison glands of fishes are simple or slightly branched acinous structures which use the holocrine method of secreting a mucuslike substance. The poison glands of snakes are modified oral or salivary glands. Amphibian glands are simple, acinous, holocrine, with granular secretion. In some cases these amphibian poison glands produce mucus by a merocrine method of secretion. These glands function as protective devices. See Gland