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The author stresses the importance of the size and myelinization of nerve fibers as indexes of their functional significance and connections. One must be on guard, however, against relying too implicitly on such histologic characteristics and attempting to determine functional significance solely on this basis. The attempt to do so has led Professor Kiss into error. He states that all unmyelinated fibers are sympathetic; that there is no evidence that any sympathetic fibers are myelinated. His assumption that all somatic motor fibers are large leads him to the conclusion that the small myelinated fibers in the ventral roots of the cervical nerves belong to the parasympathetic group. Although it is well known that the largest sensory fibers are those which supply the skeletal muscle, their histologic resemblance to somatic motor fibers causes him to question their sensory nature when he sees them in the dorsal root. The idea that all