The elementary nervous system elementarynervou00park Year: [c1919] 18 THE ELEMENTARY NERVOUS SYSTEM neurones, whose cell-bodies are situated in the integu- ment instead of being gathered into special ganglia, ex- tend, as in the vertebrates, from the skin to the central nervous organs, the brain or the ventral ganglionic chain. The motor neurones are essentially duplicates of those in the vertebrates in that their cell-bodies lie within the cen- tral organ whence their fibers extend to the appropriate FIG. 2.—Diagram of the primary sensory s and motor m neurones of the ventral gan- glioni
The elementary nervous system elementarynervou00park Year: [c1919] 18 THE ELEMENTARY NERVOUS SYSTEM neurones, whose cell-bodies are situated in the integu- ment instead of being gathered into special ganglia, ex- tend, as in the vertebrates, from the skin to the central nervous organs, the brain or the ventral ganglionic chain. The motor neurones are essentially duplicates of those in the vertebrates in that their cell-bodies lie within the cen- tral organ whence their fibers extend to the appropriate FIG. 2.—Diagram of the primary sensory s and motor m neurones of the ventral gan- glionic chain of the earthworm showing their connections with the integument i and with the muscles ms. (Modified from Retzius.) musculature. Intemuncial neurones are also abundantly present in the earthworm, though their function here, in contrast with that in the higher vertebrates, is pure nerv- ous intercommunication, for it is very unlikely that the earthworm possesses what in any strict sense of the word can be called intelligence. Thus from a morphological standpoint, the nervous systems of the higher annuals, even including such forms as the earthworm, have much in common, their three sets of interrelated neurones, sensory, motor, and internuncial, being arranged upon what is in the main a uniform plan. Considered from a physiological standpoint, the nerv- ous system with its appended parts as just sketched falls in the higher animals into three well-marked categories. On the exterior of these animals are to be found sense or receptors such as the free-nerve terminations
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