Its colour apparently made no
difference in the result. When they were illuminated by a candle,
or even by a bright paraffin lamp, they were not usually affected
at first. Nor were they when the light was alternately admitted
and shut off. Sometimes, however, they behaved very differently,
for as soon as the light fell on them, they withdrew into their
burrows with almost instantaneous rapidity. This occurred perhaps
once out of a dozen times. When they did not withdraw instantly,
they often raised the anterior tapering ends of their bodies from
the ground, as if their attention was aroused or as if surprise was
felt; or they moved their bodies from side to side as if feeling
for some object. They appeared distressed by the light; but I
doubt whether this was really the case, for on two occasions after
withdrawing slowly, they remained for a long time with their
anterior extremities protruding a little from the mouths of their
burrows, in which position they were ready for instant and complete
withdrawal.
When the light from a candle was concentrated by means of a large
lens on the anterior extremity, they generally withdrew instantly;
but this concentrated light failed to act perhaps once out of half
a dozen trials. The light was on one occasion concentrated on a
worm lying beneath water in a saucer, and it instantly withdrew
into its burrow.
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