The Animal Self: Neurobehavioral Correlates 139“9x6” b2726 Self and the Phenomenon of Life: A Biologist Examines Life from Molecules to Humanitysense organs and the oral opening are situated. Thus, ganglionization
is accompanied by centralization, encephalization and hierarchization,
and results in improved locomotion and feeding activities. In terms of
behavior, these animals exhibit not only habituation but also simple con-
ditioning.
As evolution proceeded and the head ganglion increased in size,
the brain was formed. In the octopus, the brain has 168 million cells
contained in fourteen distinctive lobes. The octopus brain is compart-
mentalized, allowing a high degree of division of labor. The octopus is
unusually clever among invertebrates, possessing a large behavioral rep-
ertoire that includes elaborate posturing, sexual display and copulation;
they have good visual acuity and are capable of maze learning, home
construction, and territorial defense.
Insects are the other invertebrates that have a well-formed ner-
vous system that includes a primitive brain. They have good visual,
olfactory (smell) and tactile (touch) senses. Their compound eyes are
good at detecting flickers of light. Their sense of smell matches the best
seen in vertebrates. Their sense of touch makes possible a meticulous
exploration of the environment. A good position sense enables them to
orient their body. These, combined with their articulated appendages
with reciprocal innervations, endow them with agility of movement and
rapidity of response, greatly enhancing the chance of survival in a dan-
gerous environment.
7.3 Nervous System of the Vertebrates
With the advent of vertebrates in the evolutionary scene, one sees enor-
mous changes in the nervous system, most of which occurred in the
brain. There was over a thousand-fold explosion in brain size, from a
centimeter in fish to 15 cm in man, and from a few grams to one and a
half kilograms. Commensurate with this is the great increase in complex-
ity of the neuronal network. Some features of the vertebrate brain and
how they evolved are shown in Figs. 7.8 and 7.9.