Q. Using examples of invertebrate nervous systems how can the process of evolutionary cephalization be described?

Considering the example of invertebrates it is observed that evolution makes the increasing of the complexity of the organisms to be accompanied by convergence of nervous cells to special structures for commanding and controlling the brain and the ganglia. In simple invertebrates, like cnidarians, the nervous cells aren't concentrated but they are found dispersed in the body. In platyhelminthes a beginning of cephalization with the anterior ganglion concentrating neurons is previously verified. In arthropods and annelids the existence of a cerebral ganglion is evident. In cephalopod the brain commands the nervous system and molluscs the cephalization is even greater.