Are Eyes ever Autophanous?

Abstract

THOSE who read Colonel Herschel's letter in NATURE of January 18 may be interested in some observations which I made during the summer upon the sight and eyes of cats. Whereas in men and monkeys the retina is backed by black pigment, as a photographer backs a plate when his camera is to be directed towards a window, in almost all other mammals it rests on a brightly burnished layer of cellular or fibrous tissue, the tapetum. It is this mirror which throws the light back to an observer who stands-between the animal and the source of light. The eye is at the same time a camera focussed to form an image of the observer on its sensitive screen and a lantern focussed to project light upon the observer. Such an arrangement appears to a photographer fatal to the formation of an image sharp in line and dot.