. Elementary entomology. Insects. ANATOMY OF INSECTS- -INTERNAL 31 Stomach. The stomach (ventriculus) is usually a simple tube somewhat larger in diameter than the esophagus or intestine, but of variable size and strength. As the food passes into the stomach it is acted upon by the secretions of the ccecal tubes (gastric cceca) which are glandular pouches, or tubes, opening into the anterior end of the stomach. Their number, size, and shape are quite vari- able, and they secrete a weak acid which emulsifies fats and con- verts albuminoids into peptones. The stomach is not lined with chitin, as
. Elementary entomology. Insects. ANATOMY OF INSECTS- -INTERNAL 31 Stomach. The stomach (ventriculus) is usually a simple tube somewhat larger in diameter than the esophagus or intestine, but of variable size and strength. As the food passes into the stomach it is acted upon by the secretions of the ccecal tubes (gastric cceca) which are glandular pouches, or tubes, opening into the anterior end of the stomach. Their number, size, and shape are quite vari- able, and they secrete a weak acid which emulsifies fats and con- verts albuminoids into peptones. The stomach is not lined with chitin, as is the rest of the alimentary tract, but is glandular and secretes a neutral or alkaline fluid which aids in the further diges- tion of the food. The chief function of the stomach, however, is to absorb the digested food and pass it into FIG. 35. Digestive canal of a carabid beetle A, esophagus ; c, crop ; d, proventriculus ; /, stomach with its caeca ; g, posterior portion of stomach ; //, intestine; /, two pairs of Malpighian tubes; /£, rectum; /, anal glands. (After Dufour) Intestine. The food passes from the stomach into the intestine through a pyloric valve which prevents its passage backward. The intestine is divided into three fairly distinct parts, the ilcnin, colon, and rectum. The length and size of these parts varies greatly ac- cording to the food of the insect, the ileum often being considerably coiled. In the ileum the digested food materials are absorbed and passed into the blood circulation ; the colon, which is often absent, contains undigested matter and waste products ; while the rectum has thick, muscular walls and expels the feces through the anus, which opens through the last segment of the abdomen. Malpighian tubes. Opening into the intestine, just back of the stomach, are several small, slender tubes, variable in number, in which uric acid is found, and which are considered to be excretory organs similar in function to the kidneys of high
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