Physiology and biochemistry in modern medicine . gang Simple form Inearthworm. J 6 Addition of association neuronsin earthworm 9anS\ Fig. 201.—Diagram to show gradual evolution of nervous system from an epithelial cell (e)and muscle fiber (m) in the sponge (/) to a specialized epithelial cell or receptor O) and musclecell in the sea anemone {2); then to a receptor and motor neuron joining in a ganglion {Gang.),in simple form seen in the earthworm (3). Most of the ganglia in this and other segmentedinvertebrates show also the internuncial or association neurons as indicated in 4. but also of im
Physiology and biochemistry in modern medicine . gang Simple form Inearthworm. J 6 Addition of association neuronsin earthworm 9anS\ Fig. 201.—Diagram to show gradual evolution of nervous system from an epithelial cell (e)and muscle fiber (m) in the sponge (/) to a specialized epithelial cell or receptor O) and musclecell in the sea anemone {2); then to a receptor and motor neuron joining in a ganglion {Gang.),in simple form seen in the earthworm (3). Most of the ganglia in this and other segmentedinvertebrates show also the internuncial or association neurons as indicated in 4. but also of imprinting on the impulse a characteristic rhythmic activitywhich brings about the contraction of the bell and the swimming movementof the animal. The network now assumes the function of an adjusteras Avell as a transmitter of impulses. So far the adjuster is an extremely simple structure, and it is possiblethat the effector and receptor organs are directly connected by fibersrunning through it. When we come to the segmented invertebrates 784 THE CENTRAL NKRVOUS SYSTEM (suc
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