MOST people are familiar with the greenish gleam which shines from the eyes of a cat when a beam of light is directed upon them at night, and are aware that the glow can be seen only when the observer's line of vision is closely parallel with the beam of light. The phenomenon has been investigated in many animals by E. P. Walker, assistant director of the National Zoological Park of the Smithsonian Institution, and his results are referred to in the current Year Book of the Institution. The apparatus used in the tests was a reflecting head lamp, similar to a hand torch, worn on the forehead and connected with a three-cell battery in his pocket. The best results were obtained with a beam of moderate intensity, the effect of an intense beam being to make the glow less conspicuous or entirely to prevent its appearance. The shining is due to reflection from some surface in the eye, but its colour and character vary with the kind of animal. Colour ranges ran from silvery to blue-green, pale gold, reddish-gold, brown, amber and pink, and while most resembled reflection from a burnished metal surface, those of crocodiles and alligators gave the observer the impression of gazing into “a brilliantly glowing pinkish opening in a dull-surfaced bed of coal”.