Fig. 6

Neurons and nervous system under various stainings. A, BLineus viridis (Nemertea), medullary cord. Silver impregnation. Note that not all neurons of a neuropile (NP) are stained (B). C, DCapitella teleta (Annelida). Anti 5HT with fluorescent secondary antibody. Note that perikaryon and neurite are stained (green). Terminal section of neurites is branched (D). E, FTetrastemma melanocephala (Nemertea), medullary cord. Azan staining (E) and Masson-Goldner-trichrome staining (F). Single neurons cannot be discriminated; perikarya of the neurons group mostly dorsal and ventral of the neuropile (NP). Neuropile and perikarya are separated by an ecm (extracellular matrix) called inner neurilemma (small arrows); groups of neurites can be seen piercing the inner neurilemma (asterisk). G-ICarinina ochracea (Nemertea), TEM. G Transverse section of several neurites. Note small spherical mitochondria (mi), neurofilaments (arrow), and dense core vesicles (v), probably containing serotonin (Trueta et al. 2012). H Sagittal section of the cephalic nerve with several neurites. Electron-density of neurites is slightly higher than in surrounding tissue. I Perikaryon with large euchromatic nucleus, peripheral neurosecretory vesicles, and large mitochondria. Perikarya are often surrounded by glial cells that are interconnected by desmosomes (arrow). gt glandular tissue, p perikaryon