| 1. | Numerous sense organs are closely associated with the nerve rings.
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| 2. | Nervous system consists of a nerve ring and many longitudinal nerve cords.
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| 3. | The nervous system is reasonably simple, consisting of a ganglionated nerve ring surrounding the pharynx.
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| 4. | Below this lies a second nerve ring, giving off two brachial nerves into each arm.
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| 5. | It consists of a central nerve ring surrounding the mouth, and radial nerves branching into the arms.
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| 6. | The nervous system usually consists of a distributed net of cells, although some species possess more organised nerve rings.
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| 7. | Two nerve rings lie close to the margin of the bell, and send fibres into the muscles and tentacles.
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| 8. | In species lacking nerve rings, the nerve cells are instead concentrated into small structures called " rhopalia ".
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| 9. | It appears quite structureless'in vivo', but histological staining makes its primitive gut, nerve ring and muscles apparent.
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| 10. | This arrangement means the brain, sub-pharyngeal ganglia and the circum-pharyngeal connectives form a nerve ring around the pharynx.
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