Page:Popular Science Monthly Volume 10.djvu/45

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35
NATURE OF THE INVERTEBRATE BRAIN.

One of the most striking characteristics of the principal nerve-centres of the cuttle-fish is the fact of the existence of a very large optic ganglion (Fig. 13, 2), in connection with a well-developed eye, on each side. Each optic lobe, according to Lockhart Clarke, is "as large as the rest of the cephalic ganglia on both sides taken together." From each of these lobes an optic peduncle passes inward to join a supra-œsophageal ganglionic mass, which bears on its surface a large bilobed ganglion (1), thought by Clarke to be homologous with the cerebral lobes of fishes. It is connected, by means of two short cords,

PSM V10 D045 Nervous system of the cuttle fish.jpg
Fig. 13. Nervous System of the Common Cuttle-fish (Sepia officinalis).

with a much smaller bilobed ganglion, known as the pharyngeal (7). This double ganglion receives nerves from what are presumed to be the organs of taste and smell, and gives off nerves to the tongue and powerful parrot-like jaws with which the creature is provided.

The supra-œsophageal mass is connected, by cords at the sides of the œsophagus, with a very large ganglion lying beneath it (4), which is partially divided into an anterior and a posterior division. The anterior division is in relation, by means of large nerves (6), with the feet and tentacles. A commissure also unites it with the pharyngeal ganglion, so that the tentacles and arms are thus able to be brought