<i>Carinoma mutabilis</i>, light micrographs of Azan stained transverse sections of the brain.

<p><b>a</b>: The cephalic nerves (<i>cn</i>) are circularly arranged around the inner margins of the head. <b>b</b>: The brain (<i>br</i>) is composed of a central neuropil (<i>np</i>) surrounded by cell somata (<i>cs</i>). The whole brain is encircled by an outer neurilemma (<i>on</i>). The two proboscidial nerves (<i>pn</i>) originate from the ventral commissural tract (<i>vct</i>). <b>c</b>: A dorsal nerve (<i>dn</i>) arises from the dorsal commissural tract, the esophageal nerves (<i>en</i>) originate from the ventral commissural tract, the brain is in its posterior part divided into a dorsal (<i>dl</i>) and ventral (<i>vl</i>) lobe. Dorso-lateral nerves (<i>dln</i>) arise from the dorsal commissural tract and merge with the dorsal lobes. d: The ventral lobes are confluent with the lateral medullary cords (<i>mc</i>), two proboscidial nerves are present (<i>pn</i>). Note the different positions of the dorsal nerve (<i>dn1–dn3</i>). e: Higher magnification of the anterior head region, showing the location of the cephalic nerves (<i>cn</i>). <i>dn</i> dorsal nerve, <i>mo</i> mouth opening.