do not build so
well, no doubt, nor in so complex a fashion as modern architects and
engineers, but they work in the same way. All these ingenious artisans
operate without organs specially adapted to accomplish the effect
which they reach. It is with such genuine industries that we have to
deal, for the most part neglecting other productions, more marvellous
in certain ways, which are formed by particular organs, or are
elaborated within the organism, and are not the result of the
intelligent effort of the individual. To this category belong the
threads which the Spider stretches, and the cocoon with which the
Caterpillar surrounds himself to shelter his metamorphosis.

_Intelligence and instinct._--By attentive observation it is possible
to find in animals all the intermediate stages between a deliberate
reflective action and an act that has become instinctive and so
inveterate to the species that it has re-acted on its body, and thus
profoundly modified it so as to produce a new organ in such a way that
the phenomena are accomplished as a simple function of vegetative
life, in the same way as respiration or digestion.

If an individual is led to reproduce often the same series of actions
it contracts a _habit_; the repetition may be so frequent that the
animal comes to accomplish it without knowing it; the brain no longer
intervenes; the spinal cord or the chain of ganglia alone govern this
order of acts, to which has been given the name of _reflex actions_. A
reflex may be so powerful as to be transmitted by heredity to the
descendants; it then becomes an _instinct_.

Thus by its nature instinct does not differ from intelligence, but is
intimately connected with it by a chain of which all the links may be
counted. The most intelligent of beings, Man, performs actions that
are purely mechanical; many indeed can with justice be called
instinctive; and, on the other hand, an animal for whom an innate
hereditary instinct is sufficient in ordinary life will give proof of
intelligence and reflection if circumstances in which his instinct is
generally efficacious become modified so that he can no longer profit
by them. Among other ingenious experiments to show the supposed
difference between instinctive and reflective acts, Fabre brings
forward the following[5]:--The _Chalicodoma_, a hymenopterous relative
of the Bees, constructs nests composed of cells formed of mud
agglutinated with saliva. The cell once constructed, t