Fig. 11. Transmission electron micrographs of radial nerve pathways. (A) Transverse section across a radial strand as in Fig. 6. The scale bar lies within the lumen of the radial canal. The inset shows a gap junction in the endoderm of the radial canal. (B) Enlarged portion of A to show small axon bundle (sab). (C) Transverse section through a longitudinal muscle bundle in the ectoderm of the manubrium. ec, ectoderm; en, endoderm; ga, giant axon; lmb, longitudinal muscle bundle; mes, mesogloea; sab, small axon bundle; sm striated swimming muscle.