User:Jtwsaddress42/Projects/Project 3/Sections/Chapter 6/The Sensori-secretory ANS & Contractile-motor BNS systems

Detlev Arendt and others have proposed on the basis of molecular data that the nervous system of bilaterians evolved from two distinct organizing centers that formed from condensations of neurons at opposite ends of the common ancestor of cnidarians and bilaterians. The apical nervous system (ANS) is associated with "sensory-neurosecretory protoneurons", while the blastoporal nervous system (BNS)is a "contractile-motor system based on axonal connections". They propose that the two systems fused in the ancestor of bilaterians to form the central nervous system.