some insects consists of two long, white cords,
which run longitudinally through the abdomen, and are dilated at
intervals into knots, consisting of collections of nerve-cells, called
ganglia. They are really nerve-centers, which receive and transmit
impulses, originate and impart nervous influence according to the nature
of their organic surroundings. The ganglia situated over the esophagus
of insects correspond to the medulla oblongata in man, in which
originate the spinal accessory, glosso-pharyngeal, and pneumogastric
nerves. The latter possess double endowments, and not only participate
in the operations of deglutition, digestion, circulation, and
respiration, but are also nerves of sensation and instinctive motion.
The suspension of respiration produces suffocation. In insects, these
ganglia are scarcely any larger than those distributed within the
abdomen, with which they connect by means of minute, nervous filaments.
Insects are nimble in their movements, and manifest instinct,
corresponding to the perfection of their muscular and nervous systems.
When we ascend to vertebrates, those animals having a backbone, the
amount of the nervous substance is greater, the organic functions are
more complex, and the actions begin to display intelligence.

Man possesses not only a complete sympathetic system, the rudiments of
which are found in worms and insects, and a complete spinal system, less
perfectly displayed in fishes, birds, and quadrupeds, but, superadded to
all these is a magnificent cerebrum, and, as we have seen, all parts of
the body are connected by the nervous system. The subtle play of sensory
and motor impulses, of sentient and spiritual forces, indicates a
perfection of nervous endowments nowhere paralleled, and barely
approached by inferior animals. This meager reference to brainless
animals, whoso knots of ganglia throughout their bodies act
automatically as little brains, shows that instinct arises
simultaneously with the development of the functions over which it
presides. Here begins rudimentary, unreasoning intelligence. It
originates within the body as an inward, vital impulse, is manifested in
an undeviating manner, and therefore displays no intention or
discretion. While Dr. Carpenter likens the human organism "to a keyed
instrument, from which any music it is capable of producing can be
called forth at the will of the performer," he compares "a bee or any
other insect to a barrel organ, which p