The developmental study on lamination of the optic tectum in relation to the retinotectal projection in chicks and chick embryos

The tectal lamination was investigated in the central part of the chick emb ryonic tectum. Two and 5 layers were observed above the neuroepithelium (NE ) on embryonic day 6 (E6) and E8, respectively. Optic fibers extended on th e surface of the tectum by E8. On E10-11, the outer tectum was composed of 2 layers, that is, a fibrous layer forming the optic fiber layer on the tec tal surface and a cellular layer showing the gradient of cell density. In t he inner tectum, the lamination was almost completed. On E12-13, the outer rectal layers, which showed the gradient of cell density, was divided into dark and light cellular layers. The dark cellular layer was divided into 2 layers on E14-15 and further into 4 layers (layer C-F in chick) on E18. On the other hand, the light cellular layer did not change until E18, but fina lly, it was divided into 2 layers (layer A and B in chick) by E20. Optic fi bers reached the bottom of the outer tectum by E14 showing different densit ies of terminals. Stratification by optic fibers was going to step into the final stage on Els. On E20, laminations according to cytoarchitectural fea tures and the optic fiber terminals were substantially completed. In the te ctum affected by destruction of the contralateral embryonic eye (E4), some cellular layers were incompletely discriminated by differences of cell dens ity.