The Formation of Vegetable Mould Through the Action of Worms | Page 8

affects worms by its
intensity and by its duration. It is only the anterior extremity of the
body, where the cerebral ganglia lie, which is affected by light, as
Hoffmeister asserts, and as I observed on many occasions. If this part is
shaded, other parts of the body may be fully illuminated, and no effect
will be produced. As these animals have no eyes, we must suppose that
the light passes through their skins, and in some manner excites their
cerebral ganglia. It appeared at first probable that the different manner
in which they were affected on different occasions might be explained,
either by the degree of extension of their skin and its consequent
transparency, or by some particular incident of the light; but I could
discover no such relation. One thing was manifest, namely, that when

worms were employed in dragging leaves into their burrows or in
eating them, and even during the short intervals whilst they rested from
their work, they either did not perceive the light or were regardless of it;
and this occurred even when the light was concentrated on them
through a large lens. So, again, whilst they are paired, they will remain
for an hour or two out of their burrows, fully exposed to the morning
light; but it appears from what Hoffmeister says that a light will
occasionally cause paired individuals to separate.
When a worm is suddenly illuminated and dashes like a rabbit into its
burrow--to use the expression employed by a friend--we are at first led
to look at the action as a reflex one. The irritation of the cerebral
ganglia appears to cause certain muscles to contract in an inevitable
manner, independently of the will or consciousness of the animal, as if
it were an automaton. But the different effect which a light produced on
different occasions, and especially the fact that a worm when in any
way 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
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