<i>Callinera grandis</i>, schematic drawing of a dorsal view on the central nervous system, based on 3D-reconstruction of 140 aligned 0.5 µm sections.

<p>The central nervous system is composed of neuropil (<i>np</i>, <i>gray</i>), which is surrounded by cell somata (<i>cs</i>, <i>blue</i>). Cephalic nerves (<i>cn</i>) are circularly arranged; the paired proboscidial nerves (<i>pn</i>, <i>yellow</i>) originate from the ventral commissural tract (<i>vct</i>). A dorsal nerve strand (<i>dn</i>) originates from the dorsal commissural tract. The branching esophageal nerves (<i>en</i>) originate from the ventral commissural tract. The lateral medullary cords (<i>mc</i>) originate ventro-caudally in the brain. The letters on the right (<b>a</b>–<b>f</b>) refer to the histological sections in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0066137#pone-0066137-g022" target="_blank">figure <b>22</b></a>.