autumn bees lengthen their existing honey cells if these are
insufficient, but in the ensuing spring they again shorten them in
order to get greater roadway between the combs. When the full combs
have become too heavy, they strengthen the walls of the uppermost or
bearing cells by thickening them with wax and propolis. If larvae of
working bees are introduced into the cells set apart for drones, the
working bees will cover these cells with the flat lids usual for this
kind of larvae, and not with the round ones that are proper for
drones. In autumn, as a general rule, bees kill their drones, but
they refrain from doing this when they have lost their queen, and
keep them to fertilise the young queen, who will be developed from
larvae that would otherwise have become working bees. Huber observed
that they defend the entrance of their hive against the inroads of
the sphinx moth by means of skilful constructions made of wax and
propolis. They only introduce propolis when they want it for the
execution of repairs, or for some other special purpose. Spiders and
caterpillars also display marvellous dexterity in the repair of their
webs if they have been damaged, and this requires powers perfectly
distinct from those requisite for the construction of a new one.

The above examples might be multiplied indefinitely, but they are
sufficient to establish the fact that instincts are not capacities
rolled, as it were, off a reel mechanically, according to an
invariable system, but that they adapt themselves most closely to the
circumstances of each case, and are capable of such great
modification and variation that at times they almost appear to cease
to be instinctive.

Many will, indeed, ascribe these modifications to conscious
deliberation on the part of the animals themselves, and it is