Amphioxus. The Amphioxus or Lancelet is a small worm or fish-like animal about two inches long, which lives half buried in the sand banks of the Mediterranean, round the Channel Islands, etc. It belongs to the phylum Chordata, and is of great interest, owing to the light it throws on the evolution of the vertebrata. It has neither skull, jaws, limbs, brain, heart, nor kidney. The possession, however, of a cartilaginous rod (the notochord), homologous (q.v.) to the vertebral column of the vertebrates, shows that it is most nearly allied to this group. The nervous cord immediately overlies the notochord, and is specialised in places to serve as organs of sight and smell. It has affinities with the Ascidians, which it connects with the vertebrate division of the chordata.