ness use the observations made
on animals in our investigations of the human system.

[Sidenote: Three distinct parts of the nervous system of man.] In the
nervous system of man our attention is therefore especially demanded by
three essentially distinct parts--the spinal cord, the sensory ganglia,
and the cerebrum. [Sidenote: They are the automatic, the instinctive,
the intellectual.] Of the first, the spinal cord, the action is
automatic; by its aid we can walk, from place to place, without
bestowing a thought on our movements; by it we swallow involuntarily; by
it we respire unconsciously. The second portion, the sensory ganglia,
is, as we have seen, the counterpart of the cephalic ganglia of
invertebrates; it is the place of reception of sensuous impressions and
the seat of consciousness. To these ganglia instinct is to be referred.
Their function is not at all impaired by the cerebrum superposed upon
them. The third portion, the cerebrum, is anatomically distinct. It is
the seat of ideas. It does not directly give rise to motions, being
obliged to employ for that purpose its intermediate automatic associated
apparatus. [Sidenote: Dominating control of the latter.] In this realm
of ideas thoughts spring forth suggestively from one another in a
perpetual train or flux, and yet the highest branch of the nervous
mechanism still retains traces of the modes of operation of the parts
from which it was developed. Its action is still often reflex. Reason is
not always able to control our emotions, as when we laugh or weep in
spite of ourselves, under the impression of some external incident. Nay,
more; the inciting cause may be, as we very well know, nothing
material--nothing but a recollection, an idea--and yet it is enough. But
these phenomena are perhaps restricted to the first or anterior lobes of
the brain, and, accordingly, we remark them most distinctly in children
and in animals. As the second and third lobes begin to exercise their
power, such effects are brought under control.

[Sidenote: Progressive nervous development in the animal series.] There
is, therefore, a regular progression, a definite improvement in the
nervous system of the animal series, the plan never varying, but being
persistently carried out, and thus offering a powerful argument for
relationship among all those successively improving forms, an
observation which becomes of the utmost interest to us in its
application to the vertebrates. In the a