Fig. 1

Chordate notochords in side views, cross sections (through the dotted line in each side view), and diagrams of the cross sections. Structures shown in the diagrams include the nerve cord (blue), notochord (red), axial musculature (green), endoderm (yellow), and gonads (purple). a–f Amphioxus, Branchiostoma lanceolatum, a–c 3-day larva and d–f adult. Tunicates: g–i late tailbud larva of an ascidian, Ciona intestinalis, and j–l an adult appendicularian, Oikopleura dioica. m–o Stage 26 larval lamprey, Petromyzon marinus. p–r Stage 24 embryonic shark, Scyliorhinus canicula. s–u) Pharyngula stage embryo of teleost, Danio rerio