Fig. 47.—A, The Formation of the Retina of the Eye of Ammocœtes (after Scott); B, The Formation of the Retina of the Eye of Ammocœtes, on my theory. "R.", retina; "l.", lens; "O.n.", optic nerve fibres; "Al.", cephalic end of invertebrate alimentary canal; "V.", cavity of ventricles of brain; "Al.d.", anterior diverticulum of alimentary canal; "op.d.", optic diverticulum.