Schemes of the sensory pathways and the differentially specialized protection systems. In contrast to the primary sensory cells situated on the epidermis, the sensory neurons are multiply covered by glial wrappers. The myelin-like repeats are only formed in the head ciliary lines and not in the ventral nerve cords. Insets: the schemes show two distinct structural types of primary sensory receptor cells of epidermis and neuronal cells of the brain and ventral nerve cords. ax, axonal fiber; ct, cuticle; gc, glial cell membranes; gry, yellow color granule; lt, line type cell; mt, mitochondrion; ss, sensilla type cell; tt1 an tt2, tuft type cell 1 or 2.