Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 NERVOUS SYSTEM. 537 The ventral chain, which with its lateral nerves may be compared to the spinal cord and the spinal nerves, preserves the primitive uniform segmentation in most larvse, and is the least modified in insects with a free prothorax and long abdomen. In such insects, not only do the three large thoracic ganglia, which supply the wings and legs with nerves, remain separate, though certainly they are often
Elementary text-book of zoology, tr Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote elementarytextbo01clau Year: 1892-1893 NERVOUS SYSTEM. 537 The ventral chain, which with its lateral nerves may be compared to the spinal cord and the spinal nerves, preserves the primitive uniform segmentation in most larvse, and is the least modified in insects with a free prothorax and long abdomen. In such insects, not only do the three large thoracic ganglia, which supply the wings and legs with nerves, remain separate, though certainly they are often strengthened by the anterior abdominal ganglia, but also a larger number of abdominal ganglia. Of the latter, the last, which is formed by the fusion of several ganglia and gives off numerous nerves to the ducts of the generative apparatus and to the rectum, is always distinguished by its considerable size. The gradually progressing concentration of the ventral cord, which may be followed out in the larval and pupal development,* is ex- plained by the crowding together of the abdominal ganglia, as well as by the fusion of the thoracic ganglia. Of the latter, those of the meso- and meta-thorax first fuse to a large pos- terior thoracic mass, which then fuses with that of the prothorax to form a common thoracic mass. When the latter is finally united to the fused mass of the abdominal ganglia, the highest grade of concentration, which is found in the Diptera and Hemip- tera, is reached. The visceral nervous system is divided into the system of the Cesophageal FlG- ganglion and ceso- phageal nerve ganglia of Sphinx nerves and the true sympathetic. In ngustri(after Newport). Gfr., Frontal the former we can distinguish unpaired &*&'*•. a', /• eanslia of the paired cesophageal nerves. ' and paired oesophageal nerves. The unpaired system springs from the anterior surface of the brain by two roots, which unite in front to form the so-called frontal ganglion (fig. 445
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