Figure 1.

Invertebrate chordate notochords. (a) Expression of the gene brachyury (Odi-T) in the developing notochord of Oikopleura dioica (image courtesy of Cristian Cañestro and Susan Bassham). (b) The Ciona intestinalis notochord visualized with a brachyury LacZ reporter gene (image courtesy of Peter Osborne). (c) The head of a juvenile amphioxus (Branchiostoma lanceolatum), with the notochord distinguishable up to the anterior-most tip of the animal's head and indicated by the arrow (image by the author).