AP BIOLOGY

Detailed explanation-1: -In earthworm, cerebral ganglions function as a simple brain which is located above pharynx and is connected to the first ventral ganglion the removal of which would result in uncontrolled movement of the worm. Neuronal and reflex pathways control the coordinated movements and behavior of the worms.

Detailed explanation-2: -Central Nervous system: It includes following structures: Cerebral ganglia-There are two pear shaped cerebral ganglia fused together at 3rd segment called brain. Circumpharyngeal connective-Two circumpharyngeal connectives arise from each cerebral ganglion laterally.

Detailed explanation-3: -Insects typically contain segmented central nervous systems, with one ganglion per body segment. However, supraesophageal ganglia (brain), subesophageal ganglia and terminal ganglia consist of multiple neuromeres that arose from fusion of individual ganglia.

Detailed explanation-4: -Thus, a complete nerve ring is formed around the pharynx. ii. Ventral nerve cord. It is white rod like structure, which starts running from sub-pharyngeal ganglia towards posterior end. In each segment, ventral nerve cord swells which is called segmental ganglia.