sensitiveness to light enables them to distinguish between day and
night; and they thus escape extreme danger from the many diurnal
animals which prey on them. Their withdrawal into their burrows
during the day appears, however, to have become an habitual action;
for worms kept in pots covered by glass plates, over which sheets
of black paper were spread, and placed before a north-east window,
remained during the day-time in their burrows and came out every
night; and they continued thus to act for a week. No doubt a
little light may have entered between the sheets of glass and the
blackened paper; but we know from the trials with coloured glass,
that worms are indifferent to a small amount of light.

Worms appear to be less sensitive to moderate radiant heat than to
a bright light. I judge of this from having held at different
times a poker heated to dull redness near some worms, at a distance
which caused a very sensible degree of warmth in my hand. One of
them took no notice; a second withdrew into its burrow, but not
quickly; the third and fourth much more quickly, and the fifth as
quickly as possible. The light from a candle, concentrated by a
lens and passing through a sheet of glass which would intercept
most of the heat-rays, generally caused a much more rapid retreat
than did the heated poker. Worms are sensitive to a low
temperature, as may be inferred from their not coming out of their
burrows during a frost.

Worms do not possess any sense of hearing. They took not the least
notice of the shrill notes from a metal whistle, which was
repeatedly sounded near them; nor did they of the deepest and
loudest tones of a bassoon. They were indifferent to shouts, if
care was taken that the breath did not strike them. When placed on