1. Hay.-Trans. Ophthal. Soc. U.K., Vol. XXXIX, p. 240.
2. Sheard.-Amer. Ji. of Phys. Optics., Vol. II, p. 168.
3. Hartrdie ai,d Owen.-Brit. Jl. of Ophthal., Vol. VI, p. 543.
4. Banister; Hartridge and Lythgoe.-Proc. Optical Convention, part ii, 1926.
5. Put a nose on this face: 2. Put a dot below this line: 3. Write g on the egg-shaped figure: CQ Q @3