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other hand, similar parts in many of the Fig. 76.—Portion of electric organ of gymuotus magnified 400 diameters. p, Pacini's line; a a, anterior papillæ; b b, posterior papillæ, sometimes called thorn papillæ. They contain cells that move (amœboid movements). n, nerve-fibres entering papillæ; x x, connective tissue. The plates sometimes cleave transversely along Pacini's line, a division analogous to the cleavage of muscle into Bowman's discs. Fig. 77.—Semi-diagrammatic view of a disc from the electric organ of the skate (Raia batis). a a, connective tissue with capillaries; b, nerve layer, nerve endings branching; c, striated layer; d d, processes of transparent structureless material containing numerous nuclei corresponding to the thorn papillæ of gymnotus. Crustacea (crabs, lobsters, etc.) may become