1!)8
WILLIAM MACNAE
and Periophthalwms have a thick cornea, and a slight hypermetropia
(Hein, 1913; Karsten, 1923; Walls, 1942). Walls has pointed out that
the retina is rich in cones, the lower half having many cones and the
upper half more rods. The upper half would be more frequently used
for locating prey on the surface of the mud; the lower half for
watching a rival in display.
The eyes are raised above the surface of the head and can be pulled
down towards the buccal cavity. This movement is frequent and seems
to serve the same function as blinking in higher tetrapods. The eyes, unlike those of frogs, are not pulled down to project into the buccal cavity.
The epithelia in the sides and back of the buccal cavity have been
said t o serve as respiratory epithelia (Schottle, 1932), and Harms
considered that accessory respiratory surfaces are present on the fins
and in diverticula of the nasal sacs (see summary accounts in Grass&,
1958). The gill surfaces, according t o Schottle, are reduced in comparison with fully aquatic gobies.
Schottle (1932) described the structure of the gills of several gobioid
fishes in order to find specializations to life on land among mangal living
species. She pointed out that while the gills of Boleophthalmus were
normal and resembled those of fully aquatic gobies, the gills of the
periophthalmines were reduced. She also described that Boleophthalmu~
has highly vascularized papillae particularly in the tail region, and that
Periophthalmus and Periophthalmodon possess a reticulum of capillaries
in the skin between the scales ; all these were claimed to be accessory
respiratory surfaces. But no one seems to have shown that these are in
fact respiratory. If this be indeed their function, one wonders how salt
balance is maintained, for all these fishes are curyhaline, occurring as
they do in waters of variable salinity.
When a mud-skipper is submerged the opercular movements are
easily seen to be similar to those of other fishes--water is drawn in
through the mouth and passed out by way of the opcrcular openings.
Stebbins and Kalk (1961), reporting on a study of the Periophthalmus
common a t Inhaca, suggest that “ undcrwater respiration does not
involve air trapped in the branchial cavity as suggested by Willem and
Boelaert (1937) ” and confirm that while under water they respire as do
other fishes for, as they describe :
When the fish comes out on land it commonly pauses at the water’s edge
and gulps air. This involves a quick distension of the branchial cavity. The
small valvular, opercular openings are closed and, with a quantity of water
held in the gill chambers as well as the trapped air, oxygen rich water is
available for gill respiration on land. The branchial region remains distcndecl
and opercular movements are suspended.
WILLIAM MACNAE
and Periophthalwms have a thick cornea, and a slight hypermetropia
(Hein, 1913; Karsten, 1923; Walls, 1942). Walls has pointed out that
the retina is rich in cones, the lower half having many cones and the
upper half more rods. The upper half would be more frequently used
for locating prey on the surface of the mud; the lower half for
watching a rival in display.
The eyes are raised above the surface of the head and can be pulled
down towards the buccal cavity. This movement is frequent and seems
to serve the same function as blinking in higher tetrapods. The eyes, unlike those of frogs, are not pulled down to project into the buccal cavity.
The epithelia in the sides and back of the buccal cavity have been
said t o serve as respiratory epithelia (Schottle, 1932), and Harms
considered that accessory respiratory surfaces are present on the fins
and in diverticula of the nasal sacs (see summary accounts in Grass&,
1958). The gill surfaces, according t o Schottle, are reduced in comparison with fully aquatic gobies.
Schottle (1932) described the structure of the gills of several gobioid
fishes in order to find specializations to life on land among mangal living
species. She pointed out that while the gills of Boleophthalmus were
normal and resembled those of fully aquatic gobies, the gills of the
periophthalmines were reduced. She also described that Boleophthalmu~
has highly vascularized papillae particularly in the tail region, and that
Periophthalmus and Periophthalmodon possess a reticulum of capillaries
in the skin between the scales ; all these were claimed to be accessory
respiratory surfaces. But no one seems to have shown that these are in
fact respiratory. If this be indeed their function, one wonders how salt
balance is maintained, for all these fishes are curyhaline, occurring as
they do in waters of variable salinity.
When a mud-skipper is submerged the opercular movements are
easily seen to be similar to those of other fishes--water is drawn in
through the mouth and passed out by way of the opcrcular openings.
Stebbins and Kalk (1961), reporting on a study of the Periophthalmus
common a t Inhaca, suggest that “ undcrwater respiration does not
involve air trapped in the branchial cavity as suggested by Willem and
Boelaert (1937) ” and confirm that while under water they respire as do
other fishes for, as they describe :
When the fish comes out on land it commonly pauses at the water’s edge
and gulps air. This involves a quick distension of the branchial cavity. The
small valvular, opercular openings are closed and, with a quantity of water
held in the gill chambers as well as the trapped air, oxygen rich water is
available for gill respiration on land. The branchial region remains distcndecl
and opercular movements are suspended.