employed and in the intervals of such employment, whatever set of muscles
and ganglia may then have been brought into play, is often regardless of
light, are opposed to the view of the sudden withdrawal being a simple
reflex action. With the higher animals, when close attention to some
object leads to the disregard of the impressions which other objects must
be producing on them, we attribute this to their attention being then
absorbed; and attention implies the presence of a mind. Every sportsman
knows that he can approach animals whilst they are grazing, fighting or
courting, much more easily than at other times. The state, also, of the
nervous system of the higher animals differs much at different times, for
instance, a horse is much more readily startled at one time than at
another. The comparison here implied between the actions of one of the
higher animals and of one so low in the scale as an earth-worm, may
appear far-fetched; for we thus attribute to the worm attention and some
mental power, nevertheless I can see no reason to doubt the justice of
the comparison.
Although worms cannot be said to possess the power of vision, their
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
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