Figure 17. Tubulanus polymorphus, light micrographs of Azan stained transverse sections of the brain.

a: The cephalic nerves (cn) are circularly arranged around the tip of the head. b: The brain (br) is composed of a central neuropil (np) which is surrounded by cell somata (cs), the ventral commissural tract (vct) connects the two halves of the brain below the rhynchocoel (ry). c: The canals (ca) of the cerebral organ (co) open ventro- laterally to the environment. The esophageal nerves (en) originate in the ventral commissural tract and are connected again shortly in front of the mouth opening (mo). Two proboscidial nerves (pn) are present. d: The ventral lobes of the brain are confluent with the lateral medullary cords. mo mouth opening, vl ventral lobes of brain.