Page:Life in Motion.djvu/202

terranean the electric organ takes the place of the outer gill muscles of the fifth gill arch. In ordinary rays, and their distant cousins the sharks, these muscles are powerful organs for moving the lower jaw, but in the torpedo for Fig. 73.—Attachment of the electric plates of torpedo to the sheath of the prism. d, sheath of prism v, ventral or nervous layer or plate; d (to the left), dorsal plate; e, fine layer of connective tissue; b, intermediate layer; n, nuclei of this layer; a, a portion reflected from the plate. these muscles electric organs have been substituted. At an early stage in the development of the torpedo the tissue of the electric organ is like that of an embryonic muscle, showing numerous nuclei, and even a distinct longitudinal and a more faint transverse striation