The center of the neural tube becomes ___________ whereas the outside tissue becomes ___________.

During the embryonic development, the center of the neural tube becomes ventricles of the brain, and the outside tissues becomes the brain tissues.  

The ventricles of the brain are the communication network composed of cerebrospinal fluid filled cavities located in the parenchyma of the brain. It is composed of 2 lateral ventricles, third and fourth ventricle.