14
JERALD J . BERNSTEIN
Recent studies in mammals and in fish have demonstrated that areas
designated as limbic portions of the telencephalon may be involved in
emotion ( Segaar, 1965).
Carefully following the development of the telencephalon, Nieuwenhuys (1963, 1966, 1967b) has concluded that the telencephalon of actinopterygians only everts and thickens. Therefore, he has not homologized
the areas of the teleostian telencephalon to higher vertebrate nervous
systems ( Nieuwenhuys, 1967b), but has divided the telencephalon into
two principal regions, the area ventralis and the area dorsalis telencephali
(Fig. 4 ) . The ventral area of the telencephalon receives secondary olfactory fibers and is a rather constant structure throughout the whole subclass of bony fishes. However, there appears to be a progressive differentiation of the dorsal telencephalic area. In the Chondrostei, Holostci,
and Teleostei neurons are located throughout the entire mass of the
telencephalic wall. These neurons comprise the nuclear masses of telencephalic gray that are identified as the telencephalic nuclei. In the
Holostei the caudal area of the area dorsalis appears to receive secondary
olfactory fibers. However, in the higher teleost fishes these fibers can
be traced almost exclusively to the caudal ventral part of the area dorsalis. In the evolutionary sequence through Chondrostei, Holostei, and
Teleostei there appears to be a decrease in the influence of the olfactory
area on the area dorsalis of the telencephalon as sequentially increasing
connections of the dorsal area of the pars dorsalis of the telencephalon
with the ventral portion of the diencephalon are observcd. In the most
advanced bony fishes, the area dorsalis telencephali and the ventral
thalamus possess increasing numbers of connections. In the teleost we
also find an advance in differentiation by an increase in the mass of the
area dorsalis telencephali, the lateral forcbrain bundle, and other areas.
The forebrain of the bony fishes appears to have developed into a highly
differentiated complex center that processes much more than olfactory
information. These neural centers have developed strong diencephalic
connections ( Nieuwenhuys, 1963, 1967b).
C. Neurophysiological Studies of the Olfactory System
Neuroanatomical and bchavioral studies suggest that olfaction plays
a major role in the behavior of fishes (Kleerekoper, 1967; Hasler, 1957,
1966; Healey, 1957). It is obvious from the anatomical data that the
influence of the telencephalic and diencephalic areas subserving olfaction
is species dependent ( Nieuwenhuys, 1967b ) , The spontaneous activity
of the neural elements in the olfactory bulb of fish also appears to
JERALD J . BERNSTEIN
Recent studies in mammals and in fish have demonstrated that areas
designated as limbic portions of the telencephalon may be involved in
emotion ( Segaar, 1965).
Carefully following the development of the telencephalon, Nieuwenhuys (1963, 1966, 1967b) has concluded that the telencephalon of actinopterygians only everts and thickens. Therefore, he has not homologized
the areas of the teleostian telencephalon to higher vertebrate nervous
systems ( Nieuwenhuys, 1967b), but has divided the telencephalon into
two principal regions, the area ventralis and the area dorsalis telencephali
(Fig. 4 ) . The ventral area of the telencephalon receives secondary olfactory fibers and is a rather constant structure throughout the whole subclass of bony fishes. However, there appears to be a progressive differentiation of the dorsal telencephalic area. In the Chondrostei, Holostci,
and Teleostei neurons are located throughout the entire mass of the
telencephalic wall. These neurons comprise the nuclear masses of telencephalic gray that are identified as the telencephalic nuclei. In the
Holostei the caudal area of the area dorsalis appears to receive secondary
olfactory fibers. However, in the higher teleost fishes these fibers can
be traced almost exclusively to the caudal ventral part of the area dorsalis. In the evolutionary sequence through Chondrostei, Holostei, and
Teleostei there appears to be a decrease in the influence of the olfactory
area on the area dorsalis of the telencephalon as sequentially increasing
connections of the dorsal area of the pars dorsalis of the telencephalon
with the ventral portion of the diencephalon are observcd. In the most
advanced bony fishes, the area dorsalis telencephali and the ventral
thalamus possess increasing numbers of connections. In the teleost we
also find an advance in differentiation by an increase in the mass of the
area dorsalis telencephali, the lateral forcbrain bundle, and other areas.
The forebrain of the bony fishes appears to have developed into a highly
differentiated complex center that processes much more than olfactory
information. These neural centers have developed strong diencephalic
connections ( Nieuwenhuys, 1963, 1967b).
C. Neurophysiological Studies of the Olfactory System
Neuroanatomical and bchavioral studies suggest that olfaction plays
a major role in the behavior of fishes (Kleerekoper, 1967; Hasler, 1957,
1966; Healey, 1957). It is obvious from the anatomical data that the
influence of the telencephalic and diencephalic areas subserving olfaction
is species dependent ( Nieuwenhuys, 1967b ) , The spontaneous activity
of the neural elements in the olfactory bulb of fish also appears to