part of develops from develops into mesectoderm anlage ectoderm mesectoderm mesectoderm anlage fly_anatomy.ontology FBbt:00000136 A double row of cells located at the midline from the end of gastrulation when the mesectoderm anlage of either side meet at the midline (Campos-Ortega and Hartenstein, 1997). Initially there are approximately eight cells per segment, which soon divide to become approximately 16 cells, but these do not have a clear metameric organization at this stage (Campos-Ortega and Hartenstein, 1997; Kearney et al., 2004). These cells become elongated during stage 8, so that one end remains exposed to the outside of the embryo at the midline, in line with the ectoderm, while the other end maintains contact with the mesoderm (Campos-Ortega and Hartenstein, 1997). MesEc UBERON:0000927 developing embryonic structure primordium mesectodermal derivative