deoxyribonucleic acid, desoxyribonucleic acid, DNA(noun) (biochemistry) a long linear polymer found in the nucleus of a cell and formed from nucleotides and shaped like a double helix; associated with the transmission of genetic information.
But even adults don't often know what a notochord is. A notochord is a primitive beginning to the backbone. It appears in embryos as a small flexible rod made from cells from the mesoderm, which is one of the three layers of cells of embryos. Notochords are only found in the phylum chordata, a group of animals that includes humans.
This tube is the cartilaginous tube spoken of above and is known as the cartilaginous sheath of the notochord. The Works of Francis Maitland Balfour, Volume III (of 4) Francis Maitland Balfour. This structure is called the notochord (a string down the back).