mud, behind which it hid until it devoured its tender morsel. Again it
swam back to the hydra and plucked from it one of its young; again it
swam back to the little mud heap, behind which it once more ensconced
itself until it was through with its meal. When we remember that this
little creature was among entirely new surroundings (for I dipped it
from a pond in a tablespoon full of water which I had poured into a
saucer), we will appreciate the fact that the water-louse evinced
conscious determination and no little memory. It probably discovered the
hydra accidentally; it then, as soon as it had secured its prey, swam
away, seeking some spot where it could eat its food without molestation.
But when it sought the hydra again and swam back to its sheltering mud
heap, it showed that it remembered the route to and from its source of
food supply and its temporary hiding-place.

At the base of a large terminal ganglion in the neuro-cephalic system of
the common garden snail, lying immediately below and between its two
"horns," will be found, I am satisfied, the centre governing its sense
of direction. For, when this portion of this ganglion is destroyed, the
snail loses its ability of returning to its home when carried only a
short distance away; otherwise, it can find its way back to its domicile
when taken what must be to it a very great distance away, indeed.
Beneath the stone coping of a brick wall surrounding the front of my
lawn, and which, on the side toward my residence, is almost flush with
the ground, many garden snails find a cool, moist, and congenial home.
Last summer I took six of these snails, and, after marking them with a
paint of zinc oxide and gum arabic, set them free on the lawn. In time,
four of these marked snails returned to their home beneath the stone
coping; two of them were probably destroyed by enemies. Again, the same
number of snails were marked, after the base of the above-mentioned
ganglion had been destroyed, and likewise set free. Although they lived
and were to be observed now and then on the trees and bushes of the
lawn, none of them ever returned to the place from which they were taken
beneath the stone coping. I have performed this experiment repeatedly,
always with like results.

These experiments show that the snail is capable of conscious effort;
furthermore, they indicate that this little animal is the possessor of a
special sense which many of the higher animals have lost in the pr