The ventral nerve cord is a chain of ganglia running posteriorly. The last ganglion is the preanal ganglion that give rise to two branches that pass dorsally into the pseudocoel to encircle the rectum forming the rectal commissure or posterior nerve ring (Figure 22.12). Peripheral nerves form a latticework of fibers that join with small commissures to supply nerves endings to sensory structures in the cuticle.