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worm lying beneath water in a saucer； and it instantly withdrew
into its burrow。 In all cases the duration of the light； unless
extremely feeble； made a great difference in the result； for worms
left exposed before a paraffin lamp or a candle invariably
retreated into their burrows within from five to fifteen minutes；
and if in the evening the pots were illuminated before the worms
had come out of their burrows； they failed to appear。
From the foregoing facts it is evident that light 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 burrowto use the expression employed by a friendwe 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 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
a table close to the keys of a piano； which was played as loudly as
possible； they remained perfectly quiet。
Although they are indifferent to undulations in the air audible by
us； they are extremely sensitive to vibrations in any solid object。
When the pots containing two worms which had remained quite
indifferent to the sound of the piano； were placed on this
instrument； and the note C in the bass clef was struck； both
instantly retreated into their burrows。 After a time they emerged；
and when G above the line in the treble clef was struck they again
retreated。 Under similar circumstances on another night one worm
dashed into its burrow on a very high note being struck only once；
and the other worm when C in the treble clef was struck。 On these
occasions the worms were not touching the sides of the pots； which
stood in saucers； so that the vibrations； before reaching their
bodies； had to pass from the sounding board of the piano； through
the saucer； the bottom of the pot and the damp； not very compact
earth on which they lay with their tails in their burrows。 They
often showed their sensitiveness when the pot in which they lived；
or the table on which the pot stood； was accidentally and lightly
struck； but they appeared less sensitive to such jars than to the
vibrations of the piano； and their sensitiveness to jars varied
much at different times。
It has often been said that if the ground is beaten or otherwise
made to tremble； worms believe that they are pursued by a mole and
leave their burrows。 From one account that I have received； I have
no doubt that this is often the case； but a gentleman informs me
that he lately saw eight or ten worms leave their burrows and crawl
about the grass on some boggy land on which two men had just
tramp