English: Fig 1. a Living adult Bahamas lancelet (Asymmetron lucayanum) with head toward right and the anus indicated by the arrowhead. The tail terminates as a slender caudal process (cp); the 0.56-mm region reconstructed by SBSEM is indicated. Scale bar = 2 mm. b Reconstructions of all the CNS cell nuclei (turquoise) in the notochord region studied. The CNS terminates (arrowhead) just ventral to notochordal tip. The yellow area indicates where about 20 CNS cells were trimmed awafy during specimen orientation. Scale bar (also applicable to c) = 50 μm. c Reconstructions of all the notochord cell nuclei in the region studied: putative stem cell nuclei are blue, Müller cell nuclei are dark yellow, and lamellar cell nuclei are red. Brackets a, b, and c indicate zones shown in detail in subsequent figures