4. CHEMORECEPTION
89
chemosensory is based on their structural resemblance to the sensory cells
of the taste buds.
C. Free Nerve Endings
There are numerous free nerve endings in the skin of fishes; these
endings are presumed to serve the so-called common chemical sense.
The free fin rays of the gourami, Trichoguster, and hake, Urophycis,
possess taste buds which are innervated by cranial and spinal nerves,
whereas those of sea robins, Prionotus, lack taste buds and the epithelium
is richly innervated only by spinal nerves (Scharrer et al., 1947; Bardach
and Case, 1965). In behavioral experiments, Scharrer et al. (1947) could
not find a clear differentiation between the two; both showed similar positive reactions in response to chemical stimulation. Both the external taste
buds and the free nerve endings are sometimes regarded as taste receptors-referred to as taste bud type and free nerve ending type, respectively ( see Bardach, 1967). Electrophysiological evidence indicates that
there are two types of nerve discharges (fast- and slow-adapting) following chemical stimulation of hake fin rays; only the fast-adapting type is
seen in sea robin fin rays. These findings suggest that the slow-adapting
discharges are characteristic of taste buds while fast-adapting discharges
may originate from the free nerve endings around taste buds (Bardach
and Case, 1965).
Reactions following stimulation of the common chemical sense are
usually negative or defense reaction. However, there are exceptions and
the biological significance of the common chemical sense remains unexplained; some even deny its existence (von Buddenbrock, 1952).
D. Morphology of Brain and Feeding Habits
Developmentally, the teleost forebrain is basically different from that
of elasmobranchs and the higher vertebrates ( Aronson, 1963). Nevertheless, the morphology of the olfactory bulb and centers are essentially
similar throughout the vertebrates although there are minor variations,
especially in relative size and position of the different areas.
Olfactory nerve fibers (filu olfuctoriu) arise in the nasal mucosa
terminate in the olfactory bulb, where they make a special synaptic contact with the bulbar neurons in the glomerulus. The fibers themselves do
not branch until they terminate. The length of these olfactory nerves
varies greatly in different fishes. They may have either short olfactory
89
chemosensory is based on their structural resemblance to the sensory cells
of the taste buds.
C. Free Nerve Endings
There are numerous free nerve endings in the skin of fishes; these
endings are presumed to serve the so-called common chemical sense.
The free fin rays of the gourami, Trichoguster, and hake, Urophycis,
possess taste buds which are innervated by cranial and spinal nerves,
whereas those of sea robins, Prionotus, lack taste buds and the epithelium
is richly innervated only by spinal nerves (Scharrer et al., 1947; Bardach
and Case, 1965). In behavioral experiments, Scharrer et al. (1947) could
not find a clear differentiation between the two; both showed similar positive reactions in response to chemical stimulation. Both the external taste
buds and the free nerve endings are sometimes regarded as taste receptors-referred to as taste bud type and free nerve ending type, respectively ( see Bardach, 1967). Electrophysiological evidence indicates that
there are two types of nerve discharges (fast- and slow-adapting) following chemical stimulation of hake fin rays; only the fast-adapting type is
seen in sea robin fin rays. These findings suggest that the slow-adapting
discharges are characteristic of taste buds while fast-adapting discharges
may originate from the free nerve endings around taste buds (Bardach
and Case, 1965).
Reactions following stimulation of the common chemical sense are
usually negative or defense reaction. However, there are exceptions and
the biological significance of the common chemical sense remains unexplained; some even deny its existence (von Buddenbrock, 1952).
D. Morphology of Brain and Feeding Habits
Developmentally, the teleost forebrain is basically different from that
of elasmobranchs and the higher vertebrates ( Aronson, 1963). Nevertheless, the morphology of the olfactory bulb and centers are essentially
similar throughout the vertebrates although there are minor variations,
especially in relative size and position of the different areas.
Olfactory nerve fibers (filu olfuctoriu) arise in the nasal mucosa
terminate in the olfactory bulb, where they make a special synaptic contact with the bulbar neurons in the glomerulus. The fibers themselves do
not branch until they terminate. The length of these olfactory nerves
varies greatly in different fishes. They may have either short olfactory