Previously, we discussed the advantages and disadvantages of asexual and sexual reproduction. We found the primary evolutionary advantage to sexual reproduction, by a halving of the chromosome number in the gametes, was genetic recombination so to form somatic cells behaving in new and unique ways. However, this selective advantage did not allow evolution to move beyond simple multicellular animals, such as sponges.
What was needed to generate more organized bodies was a nervous and circulatory system allowing  sensory information and motor commands to be transmitted over long distances via nerves,  a heart to pump nutrients to and remove wastes from organized tissues, and  an extended hormonal system.
As I am extremely busy this week, I am going to ask the serious seekers to read two good articles. Consider it as an occasional exercise of good faith!
 Evolution of the Nervous System and Brain by Gerhard Roth and Ursula Dicke at
 Evolution of Circulatory System