Page:The Zoologist, 4th series, vol 5 (1901).djvu/363

Rh therefore believe to exist. The Baboon could only represent the phenomenon under the colours as they appeared to him, but if such colours have a different appearance to me, both picture and subject would still be identical, and prove absolutely nothing. To take an extreme illustration. Suppose what is white to me is black to my Baboon, and vice versâ. If my animal faithfully paints a white flower as black, as it sees it, the picture must still show a white flower to me, because of our different sense appreciations.

Leeches (Clepsine) afford a good instance of the variety in sense perception. Prof. Whitman has paid much attention to these animals, and writes:—"Pass the hand over a dish in which a number of Clepsines are resting quietly on the bottom, and at a distance of a few inches above the animals, taking care not to make the least jar or other disturbance. If the animals are quite hungry, the slight shadow of the hand, imperceptible though it be to our eyes, will be instantly recognized by them, and a lively scene will follow, every Leech rising up, supported on its posterior sucker, and swinging at full length back and forth, from side to side, round and round, as if intensely eager to reach something. Put a Turtle in the dish, and see what a scramble there will be for a bloody feast. The shadow of the hand was to these creatures like the shadow of a Turtle swimming or floating over them in their natural haunts, and hence their quick and characteristic response. A piece of board floating over them would have the same effect. Although so sensitive to a small difference in light, the Clepsine eyes can give