The degree of cephalization shown by Cnidarians, flatworms, octopi, and vertebrates;
Cnidarians have no cephalization (nerve net); flatworms have some cephalization (ganglia); Octopi and vertebrates have higher degrees of cephalization (ganglia and brain). Cephalization is an evolutionarytrend in which, over many generations, the mouth, sense organs, and nerve ganglia become concentrated at the front end of an animal, producing a head region.
