part_of part of part of bounding layer of adjacent to neural tube neural tube lumen germinal neuroepithelium As the cells adjacent to the lumen continue to divide, the migrating cells form a second layer around the original neural tube. This layer becomes progressively thicker as more cells are added to it from the germinal neuroepithelium. This new layer is called the mantle (or intermediate) zone, and the germinal epithelium is now called the ventricular zone (and, later, the ependyma)[NCBIBook:NBK10047] embryonic tissue sensory epithelium ecto-epithelium proliferating neuroepithelium