. Animal physiology. Physiology, Comparative; Physiology, Comparative. NERVOUS SYSTEM OF INSECTS. 337 the insect, as in the Centipede, or Nereis; but in the perfect Insect the case is different; for the apparatus of locomotion is confined to the thorax (§. 103), and the segments of the abdomen have no members. We accordingly find that the ganglia of the thorax, from which the legs and wings are supplied, are very much increased in size, and are sometimes concentrated into one mass ; whilst those of the abdomen are very small, one or two of them occasionally disappearing altogether. 441. A good
. Animal physiology. Physiology, Comparative; Physiology, Comparative. NERVOUS SYSTEM OF INSECTS. 337 the insect, as in the Centipede, or Nereis; but in the perfect Insect the case is different; for the apparatus of locomotion is confined to the thorax (§. 103), and the segments of the abdomen have no members. We accordingly find that the ganglia of the thorax, from which the legs and wings are supplied, are very much increased in size, and are sometimes concentrated into one mass ; whilst those of the abdomen are very small, one or two of them occasionally disappearing altogether. 441. A good example of this curious change in the nervous system of Insects is seen in the Sphinx ligustri, or Privet Hawk- Moth, as shown in the accompanying diagrams. In Fig. 174 the nervous system of the Caterpillar is represented ; this con- sists of a pair of cephalic ganglia (1); from which proceeds, on each side, a cord of communication to the first ganglion of the trunk (2), and thence to the other ganglia (3 — 13). No difference is seen in these ganglia, except that the two last are more closely connected than the rest. The cephalic ganglia, with their cords of communication, form a ring, through which the oesophagus passes; they are situated above it; but in consequence of the reversed position of Articulated animals, the whole chain of ganglia of the trunk is situated beneath the alimentary canal (§-72).—In Fig. 175 is shown the Nervous System of the perfect Insect; in which it is seen that the whole is considerably shortened (the body of the Moth being much shorter than that of the Caterpillar), and that great changes have taken place in the relative sizes of the ganglia. The cephalic ganglia, being now connected with much more perfect eyes and other organs of sense, are greatly enlarged ; the thoracic ganglia, from. Fig. 174.—Ner- vous System of Larva of Sphinx ltgustri. Fig. 175.—Ner- vous System of Sphinx Please note that these images are extracted from
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