. Elementary entomology . m FIG. 33. Digestive and excretory system of a grasshopper r, crop; g, gizzard, or proventriculus concealed by caeca; , gastric caeca; /.*', large intes- tine ; m, mouth ; , Malpighian tubes ; o, esophagus ; r, rectum ; s, stomach ; , salivary glands ; , small intestine mouth), lying within the head, and in which it is acted upon by the saliva. In sucking insects the pharynx acts as a pumping organ, as already described. The saliva is secreted by the salivary glands, which lie along the esophagus in the thorax, whose ducts open at the base of the tongue
. Elementary entomology . m FIG. 33. Digestive and excretory system of a grasshopper r, crop; g, gizzard, or proventriculus concealed by caeca; , gastric caeca; /.*', large intes- tine ; m, mouth ; , Malpighian tubes ; o, esophagus ; r, rectum ; s, stomach ; , salivary glands ; , small intestine mouth), lying within the head, and in which it is acted upon by the saliva. In sucking insects the pharynx acts as a pumping organ, as already described. The saliva is secreted by the salivary glands, which lie along the esophagus in the thorax, whose ducts open at the base of the tongue (hypopharynx). The saliva acts on starch, changing it into glucose as in the vertebrates ; in some carnivorous insects it acts on the proteids and is sometimes used to poison the prey; in mosquitoes the poisonous saliva prevents the coagu- lation of the blood of animals, though its original function may
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