4. CHEMORECEPTION
87
though the functional significance of the trigeminal nerve is not understood, the concept of a central regulatory control over olfactory afferent
inputs has been suggested in rabbits ( Stone et ul., 1968).
The olfactory mucosa appears yellow to dark brown or black. Some
authors assume that the pigment responsible for this color has a function
in olfaction (cf. Moulton and Beidler, 1967; Moncrieff, 1967). However,
there is no report on the occurrence of pigments in the olfactory epithelium of fishes. It is, therefore, difficult to assess the role of the olfactory
pigment in the function of the olfactory membrane until we know more
about pigment location, distribution, and biochemical properties.
B. Gustatory Organ
Taste buds of elasmobranchs are restricted to the mouth and pharynx.
In teleosts they are also located on the gill rakers and gill arches, on appendages such as barbels and/or fins, and also, in some fishes, on the
entire surface of the body (Herrick, 1904). In the roof of the mouth, taste
buds are densely packed to form the palatal organ, which is innervated
by the palatine nerve in the cyprinids.
Based on the histology of the taste buds on the gill rakers and gill
arches of 24 species of teleosts, Iwai (1964) concluded that the taste
buds are more conspicuous in branchial regions of freshwater fishes than
in marine fishes. In some species of hake, Urophycis, and sea robin,
Prionotus, taste buds are on the specialized pectoral fin rays, which are
often modified into feelers (Scharrer et al., 1947; Bardach and Case, 1965;
Bardach, 1967). Taste buds are normally innervated by branches of the
n. facialis (VII), n. glossophuryngeus (IX), and n. vugus (X), which
terminate in enlarged vagal lobes. Taste buds on the modified fin rays of
the hakes are also innervated by spinal nerves.
The vertebrate taste bud is typically composed of elongated sensory
cells arranged like segments of an orange ( Fig. 4). Recent electron microscopic examination of fish taste buds has revealed the existence of three
different cell types: receptor cells, supporting cells, and basal cells
( Trujillo-Cen6z7 1961; Cordier, 1964; Desgranges, 1965; Hirata, 1966).
There are also transitional or intermediate forms of cells which may become either sensory or supporting cells. The receptor cell of Corydorar
is pear-shaped and occasionally bears few thin and short microvilli
( Trujillo-Cen6z, 1961). Desgranges ( 1965) described various types of
microvilli at the apexes of taste receptor cells in the barbels of Ameium;
these suggest different functional stages. Hirata (1966) also observed the
receptor cells with single or two apical processes of different appearance
87
though the functional significance of the trigeminal nerve is not understood, the concept of a central regulatory control over olfactory afferent
inputs has been suggested in rabbits ( Stone et ul., 1968).
The olfactory mucosa appears yellow to dark brown or black. Some
authors assume that the pigment responsible for this color has a function
in olfaction (cf. Moulton and Beidler, 1967; Moncrieff, 1967). However,
there is no report on the occurrence of pigments in the olfactory epithelium of fishes. It is, therefore, difficult to assess the role of the olfactory
pigment in the function of the olfactory membrane until we know more
about pigment location, distribution, and biochemical properties.
B. Gustatory Organ
Taste buds of elasmobranchs are restricted to the mouth and pharynx.
In teleosts they are also located on the gill rakers and gill arches, on appendages such as barbels and/or fins, and also, in some fishes, on the
entire surface of the body (Herrick, 1904). In the roof of the mouth, taste
buds are densely packed to form the palatal organ, which is innervated
by the palatine nerve in the cyprinids.
Based on the histology of the taste buds on the gill rakers and gill
arches of 24 species of teleosts, Iwai (1964) concluded that the taste
buds are more conspicuous in branchial regions of freshwater fishes than
in marine fishes. In some species of hake, Urophycis, and sea robin,
Prionotus, taste buds are on the specialized pectoral fin rays, which are
often modified into feelers (Scharrer et al., 1947; Bardach and Case, 1965;
Bardach, 1967). Taste buds are normally innervated by branches of the
n. facialis (VII), n. glossophuryngeus (IX), and n. vugus (X), which
terminate in enlarged vagal lobes. Taste buds on the modified fin rays of
the hakes are also innervated by spinal nerves.
The vertebrate taste bud is typically composed of elongated sensory
cells arranged like segments of an orange ( Fig. 4). Recent electron microscopic examination of fish taste buds has revealed the existence of three
different cell types: receptor cells, supporting cells, and basal cells
( Trujillo-Cen6z7 1961; Cordier, 1964; Desgranges, 1965; Hirata, 1966).
There are also transitional or intermediate forms of cells which may become either sensory or supporting cells. The receptor cell of Corydorar
is pear-shaped and occasionally bears few thin and short microvilli
( Trujillo-Cen6z, 1961). Desgranges ( 1965) described various types of
microvilli at the apexes of taste receptor cells in the barbels of Ameium;
these suggest different functional stages. Hirata (1966) also observed the
receptor cells with single or two apical processes of different appearance