Digestive Systems of Humans, Earthworms, and Grasshoppers The human, earthworm, and grasshopper digestive systems all have some similarities, as well as some differences. In the human digestive system, the process begins at the oral cavity (mouth). The mouth contains the teeth, tongue, and the salivary glands. The salivary glands contain saliva, salivary amylase, which breaks down starches into maltose, and mucus, which mixes with the food to form bolus. Chemical breakdown begins in the mouth. The bolus is then swallowed and passes into the pharynx. The pharynx is the structure that contains the e