How does cephalization work with a few animals? But also which is the most complex nerves?

Cephalization is the concentrated nerves in which it is at the front end. Aka the brain in which it is nerves throughout the brain and connects with the lining body of an organism. Furthermore organisms such as worms have small brain, of concentrated nerves. Primate is the most complex aka human since we have big and fragile cephalization at the head.