they may occur only once in a
lifetime. The female Yucca Moth emerges from the cocoon when the Yucca
flower puts forth its bell-like blossoms. She flies to a flower,
collects some pollen from the stamens, kneads it into a pill-like ball,
and stows this away under her chin. She flies to an older Yucca flower
and lays her eggs in some of the ovules within the seed-box, but before
she does so she has to deposit on the stigma the ball of pollen. From
this the pollen-tubes grow down and the pollen-nucleus of a tube
fertilises the egg-cell in an ovule, so that the possible seeds become
real seeds, for it is only a fraction of them that the Yucca Moth has
destroyed by using them as cradles for her eggs. Now it is plain that
the Yucca Moth has no individual experience of Yucca flowers, yet she
secures the continuance of her race by a concatenation of actions which
form part of her instinctive repertory.

From a physiological point of view instinctive behaviour is like a chain
of compound reflex actions, but in some cases, at least, there is reason
to believe that the behaviour is suffused with awareness and backed by
endeavour. This is suggested in exceptional cases where the stereotyped
routine is departed from to meet exceptional conditions. It should also
be noted that just as ants, hive bees, and wasps exhibit in most cases
purely instinctive behaviour, but move on occasion on the main line of
trial and error or of experimental initiative, so among birds and
mammals the intelligent behaviour is sometimes replaced by instinctive
routine. Perhaps there is no instinctive behaviour without a spice of
intelligence, and no intelligent behaviour without an instinctive
element. The old view that instinctive behaviour was originally
intelligent, and that instinct is "lapsed intelligence," is a tempting
one, and is suggested by the way in which habitual intelligent actions
cease in the individual to require intelligent control, but it rests on
the unproved hypothesis that the acquisitions of the individual can be
entailed on the race. It is almost certain that instinct is on a line of
evolution quite different from intelligence, and that it is nearer to
the inborn inspirations of the calculating boy or the musical genius
than to the plodding methods of intelligent learning.

Animal Intelligence

The higher reaches of the inclined plane of behaviour show intelligence
in the strict sense. They include those kinds of behaviour which