Most animals have three major pairs of salivary glands that differ in the type of secretion they produce: 1  parotid glands produce a serous, watery secretion. 2  submaxillary (mandibular) glands produce a mixed serous and mucous secretion.3  sublingual glands secrete a saliva that is predominantly mucous in character.cini in the parotid glands are almost exclusively of the serous type, while those in the sublingual glands are predominantly mucus cells. In the submaxillary glands, it is common to observe acini composed of both serous and mucus epithelial cells.