Table 2.
Species Body
length (cm)
a = Length of the ventral extension of the branchial cavity (cm)
b = Distance between the lower jaw and the ventral attachment point of the 1st gill arch (cm)
a:b
1. Gobius auratus 7.5 0.15 0.9 0.17
2. » » 6.3 0.1 0.65 0.15
3. » » 5.7 0.1 0.87 0.11
4. » » 5.6 0.1 0.6 0.17
5. Periophthalmus dipus*5P5 8.7 0.2 0.95 0.21
6. Periophthalmus chrysospilos 8.1 0.2 0.7 0.29
7. » » 8.0 0.25 0.75 0.33
8. » » 7.8 0.3 0.8 0.38
9. » » 7.7 0.25 0.7 0.36
10. » » 8.3 0.3 0.7 0.43
11. » » 8.9 0.25 0.8 0.31
12. » » 8.6 0.25 0.75 0.33
13. » » 8.7 0.3 0.8 0.38
14. Periophthalmus vulgaris*9P1 6.7 0.2 0.6 0.33
35 Bull. Fac. Fish., Nagasaki Univ. No. 101
In the bony fishes, the buccal cavity is closed by the upper and lower oral valves,*1P54 the branchial cavity by the branchiostegal membrane. In teleosts living in water, the oral valves function as back pressure flaps; they appose tightly during expiration and withdraw during inspiration. On the other hand, the branchiostegal membrane fits closely to the body during inspiration, while it moves back during expiration. In Gobius, this breathing mechanism is completely typically developed, and the structure of the breathing valves offers nothing remarkable. The maxillary and mandibular valves*2P54 (Fig. 23, Max.K. and Mand.K.) are well developed and approximately of the same size (Fig.
23). Behind the breathing valves, the mucous membrane of the buccal cavity stretches smoothly over the underlying tissue. If one compares this*1P55 to a median section through the anterior head region of Boleophthalmus boddarti*6P1 (Fig. 24), then the shortening of the maxillary and mandibular valves (Max.K. and Mand.K.) becomes clear. The buccal cavity expands dorsally behind the maxillary valve;
this recess, which has the form of a groove running parallel to the upper jaw, possesses a weakly pleated epithelium (F.d.) and is delimited by a bulge (W.) to the rear. From here to the caudal, the epithelium lining the buccal cavity is vascularized. Ventrally the buccal cavity epithelium shows two small folds (F.v.) pointing anteriorly in the recess between mandibular valve (Mand.K.) and tongue bulge (Z.).
⸻Also in Scartelaos histophorus,*7P1 a dorsal expansion is present behind the maxillary valve, which contains small folds. On the other hand, there are no ventral accessory folds.
In Periophthalmus chrysospilos (Fig. 25) the dorsal and ventral oral valves (Max.K. and Mand.K.) are also very small, but the folds behind them (F.d. and F.v.) are more strongly pronounced than in Boleophthalmus. The dorsal expansion of the buccal cavity is divided into two grooves by a fold (F.d.), which*2P55 run parallel to the upper jaw;
farther back there is a small, caudally arranged fold.
Ventrally the epithelium of the buccal cavity behind the mandibular valve is laid into several small folds (F.v), which enclose channels between them. While the form of the maxillary and mandibular valves (Max.K. and Mand.K.) is constant, the number and shape of the folds vary among the different species of Periophthalmus, and also within a species. But such accessory folds of the buccal cavity can be observed in all Periophthalmus species,*5P2
regardless of the size of the individual. If one examines the lower or upper jaw of the buccal cavity side in a total preparation, then the folds behind the narrow breathing valves and the grooves lying between them are clearly visible; they run parallel with the edges of the jaws and stretch gradually on sides. In cross sections through the head, the grooves are often not in connection with the buccal cavity. If the sections are not made exactly transverse to the longitudinal axis of the body, but more parallel with the front surface of the head, then two successive grooves are often cut as overlapping and appear as blind sacs when the series of cuts is followed (HARMS 1928, pages 299-302).*1P57 The folds can be again folded laterally in the region of the corner of the mouth*2P57, and then an image develops in the cross section, as if “blind sacs” were branching. —The lateral blind sac described by HARMS (1928) realizes through a longitudinal fold that starts from the corner of the mouth, and gradually fades toward the back.
HARMS (1928) suspects that the blind sacs in Periophthalmus vulgaris s. argentilineatus serve
Fig. 23 Median section through the anterior part of the head of
Knipowitschia panizzae.*5P1 Susa fixative, Azan staining; LEITZ Objective 1, Ocular 2, Tblg. 152, reduced to 4/5. K.K. head canal, Mand.K. mandibular valve, Max.K. maxillary valve, O.K. upper jaw, U.K. lower jaw, Z.
U.K.
36 An annotated translation of Schöttle (1931)
for the enlargement the respiratory surface. The epithelium that covers the folds and grooves is usually higher and more poorly supplied with blood vessels compared with that*3P57 of the remaining buccal cavity, in Boleophthalmus and Periophthalmus. Therefore, the functional importance of the fold and groove formation should only be seen secondarily in an enlargement of the respiratory surface. It would be more conceivable that water could be held between the folds by capillary action. Furthermore, it is possible that when the mouth*4P57 is closed, the projection*5P57 behind dorsal recessing*6P57 (Figs. 24 and 25) lies in the concavity of the lower jaw, and together with the easily adjustable folds, brings about a tighter closure of the buccal cavity.
PAPE (1914) describes completely similar accessory
folds in the front part of the buccal cavity in Heteropneustes*7P57 fossilis BL. A recess*8P57 with concentric folds protruding toward the buccal cavity occurs between the dentary and the tongue. Possibly, the folds serve for the better closure of the buccopharyngeal cavity also in this species, which possesses an outgrowth of the branchial cavity directing posteriorly as the accessory respiratory organ.
The branchiostegal membrane shows no fundamental deviations in the mud and land gobies*9P57 from Gobius. It is traversed lengthwise by the striated Musculus hyohyoideus superior (DIETZ 1914). In those forms that have the respiratory branchial cavity, the inwardly facing surface of the membrane is covered with the vascularized epithelium. The free part of the membrane is shortened in Taenioides cirratus,*4P1
Fig. 24 Median section through the anterior part of the head of Boleophthalmus boddarti.*6P1 Staining and magnification as Fig. 23. F.d. dorsal fold, F.v. ventral fold, Mand.K.
mandibular valve, Max.K. maxillary valve, N. nasal sac, O.K. upper jaw, U.K. lower jaw, W. bulge, Z.
tongue bulge.
Fig. 25 Median section through the anterior part of the head of Periophthalmus chrysospilos. Explanation as Fig. 24.
Fig. 24 Fig. 25
37 Bull. Fac. Fish., Nagasaki Univ. No. 101
Trypauchen vagina, Boleophthalmus and Periophthalmus, since the opercular cleft is very narrow. Table 3 gives data on their size and on the relationship of opercular cleft:body length among different gobies.*1P2 This ratio varies in Gobius between 1:6.5 and 1:9.7, in Periophthalmus between 1:12.7 and 1:17.0, where the mean values predominate. Boleophthalmus boddarti*6P1 shows the ratio from 1:10.2 to 1:12.6, between Gobius and Periophthalmus, while Scartelaos histophorus*7P1 has an extremely smaller opercular cleft; this species also has a special ability to inflate the gill sacs. The situation is similar with the sexually mature Taenioides cirratus,*4P1 while in a young animal the ratio of the opercular cleft to body length gives an even larger value.*1P59
The particularly good closure of the buccal and branchial cavities in the land forms cannot be linked with the fact that larger quantities of water are carried in these cavities, as some authors (CUVIER and VALENCIENNES 1837 and HAEMPEL 1913) assume. On the contrary, air is taken in such a way that the animals inspire air through the mouth by closing the gill sacs*2P59 with the branchiostegal membrane and expanding the branchial cavity.
Then they close the mouth and retain the air for some time in the buccopharyngeal cavity and the gill sac. Normally, air is expired from the mouth by compression, but expelled from the gill slit only under water (HARMS 1928, p. 303). Due to this strange breathing mechanism, a positive pressure prevails in the mouth and particularly in the inflated branchial cavity between inspiration and expiration, and the closure apparatus of these cavities must be particularly modified, in order to withstand this pressure.