sical and spiritual elements of man's
being. Even the minutest nerve-rootlets convey impressions to the dome
of thought and influence the intellectual faculties. We recognize
_muscular_ force, the strength of the body, _molecular_ force, molecules
in motion, as heat, light, chemical force, electricity, and _nervous_
force, a certain influence which reacts between the animal functions and
the cerebrum, thus connecting the conditions of the body with those of
the mind. We cannot speak of the effects of mind or body separately, but
we must consider their action and reaction upon each other, for they are
always associated. There are many difficulties in understanding this
relationship, some of which may be obviated by a study of the
development of nervous matter, and its functions in the lower orders of
organization.

Within the plant-cells is found a vital, vegetable substance termed
bioplasm, or protoplasm; which furnishes the same nutritive power as the
tissues of the polyp and jelly fish. Many families of animals have pulpy
bodies, and slight instinctive motion and sensibility, and in proportion
as the nervous system is developed, both of these powers are unfolded.
Plants have a low degree of sensibility, limited motion, respiratory and
circulatory organs. Animals possess quicker perceptions and
sensibilities, the power of voluntary motion, and, likewise a rudimental
nervous system. Some articulates have no bony skeleton, their muscles
being attached to the skin which constitutes a soft contracting
envelope. One of the simplest forms of animal life in which a nervous
system is found, is the five-rayed star-fish. In each ray there are
filaments which connect with similar nerve-filaments from other rays,
and form a circle around the digestive cavity. It probably has no
conscious perception, and its movements do not necessarily indicate
sensation or volition. In some worms a rudimentary nervous system is
sparingly distributed to the cavities of the thorax and abdomen, and, as
in the star-fish, the largest nerve-filament is found around the
esophagus, presiding over nutrition.

[Illustration: Fig. 66.]

A higher grade of organization requires a more complete arrangement of
nervous substance. Stimulus applied to one organ is readily communicated
to, and excites activity in another.

[Illustration: Fig. 67.
A. Nervous system of a Crab, showing its
ganglia. B. The nervous system of a Caterpillar.]

The nervous system of