label: visual primordium
label_lc: visual primordium
description: "Primordium that develops from the posterior procephalic region of the embryo and gives rise to visual structures of the larva and adult (Green et al., 1993; Chang et al., 2001). An optic placode forms from cells of the visual primordium when they become columnar in shape towards the end of stage 11 (Green et al., 1993; Chang et al., 2001). This placode invaginates during stages 12-13, forming a deep pouch of approximately 85 cells (Green et al., 1993). Its ventral lip segregates from the rest of the primordium and develops into the Bolwig organ (Green et al., 1993). The remainder of the placode, which will form the optic lobe, detaches from the surface of the embryo and attaches to the lateral brain, maintaining a tubular appearance until larval hatching (Green et al., 1993). Its anterior and posterior domains will become the larval inner and outer optic anlage, respectively (Chang et al., 2001). The cells that will become the eye disc are anterior and dorsal to the optic lobe placode cells (Chang et al., 2001). They move into the interior of the embryo during head involution, when they are pushed under the dorsal ridge (Huang et al., 2017)."