Procephalothrix filiformis, light micrographs of Azan stained neurons.

a: Transverse section, overview of the brain, position of the three different types of neurons (S1–S3). b: Higher magnification of somata of type 1 and 2 neurons (S1, S2). Nuclei of S1 dye orange and the cell bodies are beak shaped. Cell bodies of S2 are circular and enlarged. Nuclei dye orange. c: The nuclei of cell somata type 3 (S3) also stain orange. The cell bodies are circular but more prominent than in S1–S2. in inner neurilemma, np neuropil.