Elementary lessons on insects elementarylesson00need Year: 1928 18 ELEMENTARY LESSONS ON INSECTS few at the rear end), extended lengthwise beneath the food tube on the ventral side. In the top of the head there is a brain from wh,ich two nerve bundles descend, surrounding the front end of the food tube, to join the foremost of the ventral ganglia. So much of structure insects have in com- mon with other Arthropods. The food tube or alimentary canal begins at the mouth. Here there are minute paired salivary glands opening into it. It soon narrows down to a slender tubular esophagus or Head
Elementary lessons on insects elementarylesson00need Year: 1928 18 ELEMENTARY LESSONS ON INSECTS few at the rear end), extended lengthwise beneath the food tube on the ventral side. In the top of the head there is a brain from wh,ich two nerve bundles descend, surrounding the front end of the food tube, to join the foremost of the ventral ganglia. So much of structure insects have in com- mon with other Arthropods. The food tube or alimentary canal begins at the mouth. Here there are minute paired salivary glands opening into it. It soon narrows down to a slender tubular esophagus or Head Fig. 6.—Diagram of the internal plan of structure of a stonefly. Body wall marked as before Head, thorax (I, II, III) and abdomen (1 to 10), with antennae (a) at the front and tails or cerci— (/) at the rear—the inner food tube or alimentary canal begins at the mouth (m) and extends to rearward in esophagus (e), crop (c), proventriculus or gizzard (p), stomach (s) with a whorl of renal or Malpighian tubules at its rear end), intestine, (i) and rectum (r) to end at the anus (an). Underneath the intestine lie the paired reproductive organs (ovaries or spermaries, according to sex) opening to rearward at gn. Opening into the mouth are paired salivary glands (gl). jAbove the food tube lies the dorsal vessel or heart (). The central parts of the nervous system are shown in solid black; brain or cerebral ganglion (br) above the esophagus, and chain of ventral ganglia () on the floor of the body cavity. gullet. It widens again sometimes into a thin-walled food receptacle called a crop, or into a thick-walled chewing stomach called a gizzard, or both. So far it is lined with chitin, mostly thin, but in the gizzard the chitin often forms teeth or ridges that are useful for grinding and mixing the food. Then comes the stomach proper, whose naked walls are
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