Nevertheless it is
incredible that instincts should have been developed in reference
to objects, such as the leaves of petioles of foreign plants,
wholly unknown to the progenitors of the worms which act in the
described manner. Nor are their actions so unvarying or inevitable
as are most true instincts.
As worms are not guided by special instincts in each particular
case, though possessing a general instinct to plug up their
burrows, and as chance is excluded, the next most probable
conclusion seems to be that they try in many different ways to draw
in objects, and at last succeed in some one way. But it is
surprising that an animal so low in the scale as a worm should have
the capacity for acting in this manner, as many higher animals have
no such capacity. For instance, ants may be seen vainly trying to
drag an object transversely to their course, which could be easily
drawn longitudinally; though after a time they generally act in a
wiser manner, M. Fabre states {33} that a Sphex--an insect
belonging to the same highly-endowed order with ants--stocks its
nest with paralysed grass-hoppers, which are invariably dragged
into the burrow by their antennae. When these were cut off close
to the head, the Sphex seized the palpi; but when these were
likewise cut off, the attempt to drag its prey into the burrow was
given up in despair.
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