Figure 16. Tubulanus polymorphus, drawing of a dorsal view on the central nervous system, based on 3D-reconstruction of 173 aligned 0.5 µm sections.

The nervous system is composed of neuropil (np, gray) which may be surrounded by cell somata (cs, blue). Cephalic nerves (cn) are circularly arranged around the animal's head, and the paired proboscidial (pn, yellow) nerves originate from the ventral commissural tract (vct). A dorsal nerve (dn) originates from the dorsal commissural tract (dct). The cerebral organs (co, green) contact to the environment via small canals (ca) which open laterally. The cerebral organ is connected to the dorsal lobe of the brain. The branching esophageal nerves (en) originate from the ventral commissural tract. The lateral medullary cords (mc) originate in the ventral lobes of the brain. The letters on the right (a–d) refer to the histological sections in figure 17 .