Nervous System of Earthworm
Anatomy of Earthworm,Cockroach & Frog of Class 11
- Earthworm has a well developed nervous system; it has brainbut no head.
- Brain lies above pharynx, made up of a pair of supra-pharyngeal (cerebral) ganglia.
- A solid ventral nerve cord arises from supra-pharyngeal ganglion.
- Ventral nerve cord possesses segmental ganglia in each segment with three pairs of nerves.
- Structures typically represented in every body segment of earthworm are ganglia.
Fig. Nervous system of Pheretima
Nerves in earthworm are motor, sensory and adjustor (association neurons).
Sense organs in earthworm are quite simple. Three types are :
(a) Epidermal receptors (tangoreceptors)
(b) Buccal receptors (gustatory and olfactory) and
(c) Photoreceptors (with L-shaped lens or optic organelles or phaosome) on the surface of skin on dorsal side.
Fig. Receptors of Pheretima: A. Epidermal; B. Buccal; C. Photoreceptor
Earthworm has no eyes. Photoreceptors are used to judge intensity and duration of light, do not have the capacity of vision.