300
G. SHELTON
tion by variation of the cross sectional area of mouth, buccal cavity,
and opercular openings.
Fish in the second group of Baglioni’s classification are largely bottom-living animals in which the branchiostegal apparatus is of greater
importance in breathing. In general there is a relative increase in the
size of the opercular cavity and in the predominance of the opercular
pump in fish of this group (Fig. 3b). There is also a tendency to reduce
the size of the exhalent openings, to increase the duration of the inspiratory phase, and therefore to eject water over a short period of
time and at high velocity. These features can be seen in several fish
(Henschel, 1941; Willem, 1947; Hughes, 1960b); Callionymus is a good
example (Fig. 3b).
Baglioni’s group I11 animals are those in which the branchiostegal
apparatus is best developed and are true benthic forms. Hughes (1960b)
examined two pleuronectid fish and again found a dominant opercular
pump, although it was not obviously, different from that of group I1
fish. The main point of interest was the absence of a reversed differential
pressure in phase 4 (Fig. 3d and 3e), and Hughes attributed this to an
active branchiostegal valve mechanism. However, a number of types of
fish have been found to possess patterns of this sort (Hughes, 1960b;
Saunders, 1961; Muir and Buckley, 1967), and it may be that timing of
the movements is of more significance than active valve mechanisms.
The relative importance of upper and lower opercular cavities in
pleuronectids is a matter of some interest. Hughes (1960b) cited the
earlier work and concluded from his own experiments that water left
through both opercular openings. He also demonstrated that the gill
area was identical on the two sides. A channel connecting the two
opercular cavities was described by Yazdani and Alexander (1967) who
found that, although both gills were ventilated, water left only from
the upper operculum. This view was corroborated by Arnold (1967)
who observed the respiratory currents when the fish were in still and in
moving water. He found that water left only from the upper operculum
even when the ventilation movements were large, provided the fish was
in contact with the substrate. Actively swimming plaice, observed in
a flume, breathed through both opercular openings.
The fish in group IV are a heterogenous collection of families between which there is no clear ecological relationship. They are characterized by the loss of the branchiostegal apparatus, but this is not sufficient
to impose any uniformity in breathing mechanism. The buccal pump
(Fig. 3c) or opercular pump may be dominant in different species.
c. The G i l l Resistance. It was suggested that the concept of the dual
pump rests on a gill curtain offering appreciable resistance to water
G. SHELTON
tion by variation of the cross sectional area of mouth, buccal cavity,
and opercular openings.
Fish in the second group of Baglioni’s classification are largely bottom-living animals in which the branchiostegal apparatus is of greater
importance in breathing. In general there is a relative increase in the
size of the opercular cavity and in the predominance of the opercular
pump in fish of this group (Fig. 3b). There is also a tendency to reduce
the size of the exhalent openings, to increase the duration of the inspiratory phase, and therefore to eject water over a short period of
time and at high velocity. These features can be seen in several fish
(Henschel, 1941; Willem, 1947; Hughes, 1960b); Callionymus is a good
example (Fig. 3b).
Baglioni’s group I11 animals are those in which the branchiostegal
apparatus is best developed and are true benthic forms. Hughes (1960b)
examined two pleuronectid fish and again found a dominant opercular
pump, although it was not obviously, different from that of group I1
fish. The main point of interest was the absence of a reversed differential
pressure in phase 4 (Fig. 3d and 3e), and Hughes attributed this to an
active branchiostegal valve mechanism. However, a number of types of
fish have been found to possess patterns of this sort (Hughes, 1960b;
Saunders, 1961; Muir and Buckley, 1967), and it may be that timing of
the movements is of more significance than active valve mechanisms.
The relative importance of upper and lower opercular cavities in
pleuronectids is a matter of some interest. Hughes (1960b) cited the
earlier work and concluded from his own experiments that water left
through both opercular openings. He also demonstrated that the gill
area was identical on the two sides. A channel connecting the two
opercular cavities was described by Yazdani and Alexander (1967) who
found that, although both gills were ventilated, water left only from
the upper operculum. This view was corroborated by Arnold (1967)
who observed the respiratory currents when the fish were in still and in
moving water. He found that water left only from the upper operculum
even when the ventilation movements were large, provided the fish was
in contact with the substrate. Actively swimming plaice, observed in
a flume, breathed through both opercular openings.
The fish in group IV are a heterogenous collection of families between which there is no clear ecological relationship. They are characterized by the loss of the branchiostegal apparatus, but this is not sufficient
to impose any uniformity in breathing mechanism. The buccal pump
(Fig. 3c) or opercular pump may be dominant in different species.
c. The G i l l Resistance. It was suggested that the concept of the dual
pump rests on a gill curtain offering appreciable resistance to water