that in most cases a certain time is requisite for its action.
These statements led me to watch on many successive nights worms
kept in pots, which were protected from currents of air by means of
glass plates. The pots were approached very gently, in order that
no vibration of the floor should be caused. When under these
circumstances worms were illuminated by a bull's-eye lantern having
slides of dark red and blue glass, which intercepted so much light
that they could be seen only with some difficulty, they were not at
all affected by this amount of light, however long they were
exposed to it. The light, as far as I could judge, was brighter
than that from the full moon. 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;