ch seems to indicate a different kind of
operation carried on by the nervous system, but a moment's thought will
show that an instinctive act is simply a complex group of reflex acts. The
physical basis and ultimate unit is a cell, and the functional unit is
likewise a cell act; therefore the seeming difference proves to be one
merely of degree and not of kind. The greater complexity of the worm's
nervous system as compared with that of _Hydra_ gives to the whole
mechanism a plasticity that diverts the attention from the mechanical
nature of the entire instinctive act and of its basic cell elements.

The instinct, like the elementary reflex, is determined by heredity.
Because a certain configuration of the cells and fibers making up a
nervous system is inherited as well as the characters of the constituent
elements themselves, a worm or an insect is enabled to act as it does. A
butterfly does not have to learn how to fly, for it flies instinctively.
When it emerges from its chrysalis with its complete adult series of wings
and muscles, it has also the nervous mechanism by which these parts are
mechanically controlled. A ground-wasp deposits its eggs in a small burrow
in which it places also a caterpillar or a grasshopper paralyzed by
stinging, so that when the larva is hatched from an egg it finds an ample
supply of fresh food provided by a complex series of its mother's acts
that seem to be directed by conscious maternal solicitude. When the larva
passes through the later stages of development and makes its way to the
open air as a fully formed adult, it in its turn may go through the same
course of action as its parent, but it is clear that it cannot have any
remembrance of its mother's work or any personal knowledge of the value of
burying its own eggs in a chamber with a living prisoner to serve as food.
It was an egg when its parent did these things; as a parent itself it does
not remain on watch to see how beneficial or fruitless its acts may be. A
mechanism produced by nature's methods, the ground-wasp behaves as it is
capable of working with its inherited structure and its inherited
instinctive powers of cooerdination and sensation.

The complex lives of communal insects like ants and bees bring us to the
level of mentality where an understanding of causes and effects seems to
be the guide for conduct. Nevertheless the facts do not warrant the
assumption that reason and intelligence play any part in the mental li