Note 9 — Chapter XIII · THE SENSE OF SMELL

I make my experiments the same evening, filling a large earthen pan with fresh, sifted sand. With a stick as thick as my finger, I make six vertical tunnels in the sand, two decimetres9 deep and placed at a suitable distance apart. A hydnocystis is lowered to the bottom of each; and I insert a fine straw, to show me the exact position later. Lastly, I fill up the six cavities with caked sand. When this surface has been carefully smoothed, so that the level is everywhere the same, except for the six straws, landmarks that mean nothing to the Bolboceras, I let loose my captives, covering them with a wire-gauze cage. There are eight of them.