The mucopolysaccharide content of different epidermal structures in Gymnarchus niloticus has been demonstrated by two histochemical methods, periodic acid Schiff (P.A.S.) and toluidine blue. Mucopolysaccharides are present in the cytoplasm of the superficial cells and in the three specific cutaneous sensory organs of the lateral line system, type A, B and C. The superficial epidermal cells contain only neutral mucopolysaccharide. The mucopolysaccharides of the intraepidermal cavities in the type B and C organs as well as in the pores of the type A organ are acid; the metachromatic reaction of the toluidine blue demonstrates the presence of an acid carboxylic radicle. Histochemical analysis of the pore contents of the type A organ reveals that the mucus in the pore is acid while that of the sensory cell invagination is neutral. Histochemical differences were determined between the two sensory cells of the organ type C: the cytoplasm of the small sensory cell contains acid mucopolysaccharides while that of the large sensory cell is free of it, although the cytoplasmic invagination (extracellular) of the latter is filled with acid mucus. The results suggest that the mucus in each organ type is produced by the supporting cells surrounding the sensory cells. © 1969 Springer-Verlag.
