Popular Science Monthly/Volume 11/May 1877/Gar-Pikes, Old and Young I
THE
POPULAR SCIENCE
MONTHLY.
MAY, 1877.
| GAR-PIKES, OLD AND YOUNG. |
By Professor BURT G. WILDER,
OF CORNELL UNIVERSITY.
I.
SOME readers of The Popular Science Monthly may never have seen gar-pikes, or even heard of them. The word does not occur in some of the dictionaries, and the animals themselves are found alive only in certain parts of the world. So, before telling what gar-pikes do, it is necessary to explain what they are.
Fig. 1.—The Short-nosed Gar-Pike (Lepidosteus plaiysiomus)
Nearly adult, one-fourth natural length. O, the gill cover, or operculum. P, the pectoral, and Ve, the ventral, fin of the left side. D and A, the dorsal and anal fins. DF and VF, the "fulcra" which cover the dorsal and ventral borders of the root of the tail. X indicates the point where the section shown in Fig. 3 was made. The scales are shown in the next figure.
In the first place, the gar-pike is not a weapon, but a vertebrated animal. The vertebrates include all animals having a spine or back-bone made up of a series of segments or vertebræ. But this common definition is not wholly accurate. For the very young of man and monkeys, quadrupeds and birds, reptiles and fishes, have no skeleton at all; and some of the lowest fishes, the Amphioxus and the lamprey-eels, have no bones. So the vertebrates are now said to include all animals having a longitudinal axis or spine (whether membrane, cartilage, or bone) separating an upper or dorsal cavity, containing the spinal cord and brain, from a lower or ventral cavity, containing the stomach, intestine, heart, and other organs of vegetative life. This is shown in Fig. 3.
Let us now go one step further and learn what kind of a vertebrate is the gar-pike. At present the most natural primary subdivision of the branch seems to be into three great groups. The highest
Fig. 2.—Part of the Side of the Body of Lepidosteus platystomus,
Natural size, showing the arrangement of the enameled scales. Below is an outline of a single scale; the point is covered by the scale in front.
is the Mammalia, comprising our common quadrupeds, also bats, monkeys and men, seals and whales. The females of all these bring forth their young alive, and nourish them with milk.
Next come the Sauropsida, including birds, turtles, crocodiles, lizards, and snakes. Lastly, the Ichthyopsida, embracing the Batrachians (frogs, toads, and salamanders), and all other vertebrates.
Evidently, our gar-pike is neither a mammal nor a bird, a turtle, a snake, nor a lizard. It does look a little like an alligator, but it has not only fins and scales, but also gills, which are not known to exist in any reptile; while all the Ichthyopsida have gills during at least a part of their lives. The gar-pike is neither a frog nor a toad; it has scales and fin-rays unlike salamanders. Why, then, not call it a fish?
Fig. 3.—Cross-Section (Natural Size) of the Short-nosed gar-pike (Lepidosteus platystomus),
Showing the general arrangement of the organs which is characteristic of vertebrates. The section is made in front of the ventral fins at the point indicated by X on Fig. 1. The cut surface is looked at from behind. Near the middle is the vertebral column or backbone (VC). Above it is the spinal cord (SC), surrounded by bony walls. Below are the abdominal viscera and A is the median aorta. V V the lateral veins. MA is the median channel of the air-bladder, and LA, LA, are its lateral chambers. The cavity of the stomach (Al) is on the left, and the liver (L). with two veins, on the right. O, O are the two ovaries, of which the left lies farther forward so that its section is smaller. The whole is surrounded by the muscular walls of the body (M, M, M, M), and this again is covered by the plates of the skin.
Because, unfortunately, we are not sure that there are any "fishes." The terms "beast, bird, and fish," notwithstanding common usage and the sanction of Scripture, are devoid of scientific accuracy. For "beast" includes turtles and alligators, and excludes the aquatic mammals, whales, porpoises, manatee, and dugong. "Bird" includes bats and pterodactyls, and excludes the ostriches and penguins, which cannot fly. So "fish" is not only held by some persons to embrace the aquatic mammals, but also, when employed in a stricter sense, it includes forms differing among themselves in many important points.
At any rate, the "fish-like vertebrates" present the following well-marked groups:
1. Amphioxus lanceolatus; the lancelet. A single genus with perhaps a single species, but so peculiar as to have received the following appellations: Branchiostoma, Cirrostomi, Pharyngobranchii, Leptocardia, Acrania, Entomocrania, Dermopteri.
2. Myzonts, or Marsipobranchii; the hag-fishes and lamprey-eels.
3. Plagiostomes, or Elasmobranchii; sharks and skates.
4. Holocephala; the Chimœra and Callorhynchus.
5. Ganoids; the sturgeons (Acipenser and Scaphyrhynchus); the spoonbill (Polyodon); the mud-fish (Amia); the gar-pike (Lepidosteus); and the Polypterus and Calamoichthys of Africa, with many fossil forms.
6. Dipnoans; the mud-fishes of Africa, South America, and Australia (Protopterus, Lepidosiren, and Ceratodus).
All of the above were formerly, and are now popularly, regarded as fishes.
But the fishes, proper, or ordinary fishes, are now called:
7. Teleosts; the perch, salmon, cod, mackerel, and all others not included within the other six groups.
Some have included Amphioxus with the Myzonts; others the Plagiostomes with the Ganoids. The most natural combination seems to be that of the Ganoids with the Teleosts; and to this larger group the term Pisces has been applied. But for the present it is safer to recognize the distinctions, and to make our generalizations more exact.
What, then, is a gar-pike? Is it a Ganoid or a Teleost? Curiously enough, the prefix "gar" (signifying a dart or pointed weapon) is employed to designate two fishes, of which one (Belone) is a marine Teleost, and the other (Lepidosteus) is a fluviatile Ganoid. Both have long jaws with sharp teeth, but in other respects they are very unlike. It will be better to call Belone the "gar-fish" and Lepidosteus the gar-pike.[1]
The general appearance of the gar-pike is sufficiently indicated by the figure. The body is an elongated cylinder covered with hard and shining scales closely joined, and leaving as vulnerable points only the throat and gills, the eyes, and the parts just under the pectoral fins. The tail is moderate in size and rounded, the longest rays a little above the middle, so that it is not quite symmetrical. Upon the hinder part of the back is the dorsal fin, and below the dorsal an anal fin, immediately in front of which is the vent or outlet of the alimentary canal. The paired fins, pectoral and ventral, occupy the places natural to them as representatives of the anterior and posterior limbs of salamanders and alligators.
The length of the head varies in the different species, but, whether longer or shorter, the jaws are furnished with rows of very sharp and closely-set teeth. The apparent form of these teeth is a simple elongated cone; but it has been shown by Prof. Jeffries Wyman that their surface is really deeply folded, so that a cross-section resembles that of the teeth of the curious fossil Batrachians, called, for that reason, Labyrinthodonts. The eyes are of moderate size. As with ordinary fishes, the ears do not appear externally. The nostrils are two pair of small holes at the tip of the snout, communicating with an olfactory sac on each side; the lining of this sac presents one median longitudinal and many transverse folds.
The genus Lepidosteus, according to Huxley, has not been found earlier than the Tertiary rocks; although the family Lepidosteidæ is represented by more or less numerous genera as far back as the Carboniferous and perhaps (by Cheirolepis) in the Devonian.
True gar-pikes are not found in Europe, Asia, Africa, or Australia, or in South America; while in North America they seem to be nearly confined to the Mississippi River and its tributaries, and the Great Lakes.[2]
Prof. Poey has also recorded the existence of a gar-pike in Cuba, a fact which is interesting, not as an indication of "manifest destiny," but as a memorial of the supposed ancient connection between the West India Islands and our continent. None have been found in saltwater, and the writer has no knowledge as to how far they enter the mixed water at the mouth of the Mississippi; but their tenacity of life encourages the belief that they might possibly adapt themselves to the ocean. Their introduction into New England waters would afford to Eastern zoölogists the much-desired opportunity of studying their development, of which nothing whatever is known.
We must now inquire whether there are more than one species of Lepidosteus.
Unfortunately, this question involves several others. For the genus Lepidosteus, established by Lacepede for the single species osseus, has since been subdivided by some authors into Lepidosteus, Cylindrosteus, and Litholepis, or Atractosteus; and nearly forty specific names have been applied. One of these, Sarchirus, merely denotes the lobed state of the pectoral fin of the young gar (as will be shown further on), and most of the others seem to be based upon individual or geographical variations. Much more remains to be learned before the exact number of species can be ascertained; meantime, we may safely admit the three following:
L. osseus, the bony gar, having a long and narrow snout, and rarely attaining five feet in length; L. platystomus, the short-nosed gar, with a short and broad snout, as the name implies; and L. adamantinus, the alligator-gar or diamond-gar, with a short and wide snout, but attaining a greater size than the other two, and more common in the southern part of the Mississippi Valley. Probably the careful comparison of many individuals will oblige us to admit one or two additional species.
Notwithstanding, however, the peculiarities by which several of the species of Lepidosteus may be distinguished, so many and so obvious are the features which unite them together, and separate them from all other fishes, that they are recognized by all as belonging together, just as are the catfishes, the suckers, or the sturgeons.
Moreover, their internal structure, so far as it has been ascertained, presents a remarkable uniformity, whence we may infer that there is no important difference in their functions or habits, excepting in so far as may depend upon their circumstances, their food, etc. It is desirable to ascertain the extent of this variation, by accurate observation of carefully-determined examples, but on the present occasion we must be content, although unwillingly, with the assumption that what one gar has done another gar can do.[3]
Like most other New England zoölogists, the writer had been long obliged to content himself with dead gar-pikes, and with the somewhat unsatisfactory figures and descriptions which occur in a few zoölogical works. He had gained some more vivid impressions from the words and blackboard sketches of him who regarded "the establishment of the order of Ganoids as the most important advance which he had brought about in ichthyology."[4]
But even these privileges only increased the desire to behold the gar alive and active, and to realize the delight expressed by the great teacher when first enabled to observe them upon his journey to Lake Superior.
When, therefore, the writer found himself upon the Illinois River (at Peoria, Illinois), his steps almost instinctively sought the water, in the somewhat unreasonable expectation of being first greeted by a majestic "gar," rather than by some of the many kinds of ordinary fish so abundant in the Western rivers.
The first glance was disappointing. The river here widens into a basin known as Peoria Lake; and from the fishermen's pier, projecting some forty feet from the shore, could be seen no sign, near or remote, of the hoped-for mail-clad fish. The fishermen, who had not yet become acquainted with that unnatural perversity of naturalists which causes them to prize some things inversely as their beauty, their gentleness, and their commercial value, called attention to the "cats," "buffaloes," and other marketable fish swarming in the sunken pens, and promised to bring in some gars from their next haul; adding some emphatic statements as to the superabundance of these and of other such trash.
Just then, gliding slowly about very near the surface, and apparently undisturbed by the splashing of the bulky "cats" and "buffaloes," was seen a slender little fish less than three inches long. It was a young gar-pike. It might easily have escaped between the bars of the tanks, but instead remained within arm's-length of the edge of the open trap, moving gently to and fro as if courting observation.
A tin cup was anxiously brought: it was dipped into the water, slowly approached, and quickly lifted. The gar was there. But, floating as usual at the surface, a slight tilting of the cup spilt it back again into the water. To the astonishment of all, it soon reappeared in its former place, seeming actually to welcome death for the sake of (scientific) immortality.
By a second and more careful effort the young gar was secured, and soon transferred to the basin of water which was destined to be its home for three weeks.
During that time a part of each day was spent in observation of its form and its movements, and in comparing it with other gars, old and young.
Their Habits.—None of the young gars observed by the writer showed any disposition to attack each other or the small fishes placed with them; and the stomachs of the two adults examined with reference to this point contained only a few grasshoppers. But the many and sharp teeth are evidently well fitted for seizing living and active prey, and the fishermen accuse the gars of destroying large numbers of food-fishes. On this account, as also in revenge for the damage done by them when entangled in the nets, the fishermen are said to throw them out upon the bank to die, or to plunge them forcibly head first into the soft mud. More information is needed as to the food of the gar.
The following brief account of their manner of feeding is from a report of some remarks of Prof. Agassiz on young, living gar-pikes from Lake Ontario, before the Boston Society of Natural History, in 1856:
"The manner of feeding also is unlike that of other fishes, and resembles that of reptiles. Other fishes take their food and swallow it at once, with open mouth. But this one (the young gar) approaches its prey (in this case small minnows) slyly, sidewise, and, suddenly seizing it, holds it in its jaws until, by a series of movements, it succeeds in getting it into a proper position for swallowing, as is the habit with lizards and alligators."
Before attaching much importance to the reptilian analogies here suggested, it should be ascertained whether the mode of swallowing above described is not followed by certain long-billed Teleosts (as Belone, etc.), and, on the other hand, discarded by the short-headed gar, whose jaws have nearly the form of the pickerel. Upon the whole, the gars and other typical Ganoids seem to have affinities with Batrachians rather than with scaly reptiles.
The flesh of the gar is soft, and speedily decays. In Wood's "Natural History," it is stated that "the flesh of the bony pike is said to be good;" and Prof. W. S. Barnard informs me that the gars, especially the young, are not infrequently used as food by whites in Wisconsin, and by both whites and negroes in Mississippi. Still, there is no reason for believing that the flesh is particularly desirable.
In this connection, it is worth noting that little use as food is made by man of the representatives of the Ganoids and the Plagiostomes, which, as shown by fossil remains, were created before the ordinary fishes. Some kinds of skates are eaten on the French "coast, and sturgeons are known as "Albany beef," but no comparison can be made between them and the salmon, the cod, or the mackerel.
While watching the living gar, whether old or young, one of the first things noted is that it not only remains usually near the surface, but, at short intervals, actually protrudes the head from the water. In so doing, it turns partly over upon one side, emits a large bubble of air, executes a slight gulping movement of the jaws and throat, and sinks again below the surface; immediately afterward a few smaller bubbles escape from the gill-slit on each side of the neck. The foregoing is a very bald and inadequate description of a curious and, when first observed, astonishing operation. The movements are very rapid, and almost convulsive, as if the fish were suddenly oppressed by something, and hastened to remove it. The little gar first obtained almost invariably turned upon the left side, the air escaping from the right; this uniformity was not observed with the others. Occasionally they would open the jaws widely, as if gaping; and at other times the sides of the mouth were spread laterally.
With reference to the young gars from Lake Ontario already mentioned. Prof. Agassiz is reported as follows: "This fish is remarkable for the large quantity of air which escapes from its mouth. The source of this air he has not been able to determine. At certain times it approaches the surface of the water, and seems to take in air, but he could not think that so large a quantity as is seen adhering in the form of bubbles to the sides of the gills could have been swallowed, nor could he suppose that it could be secreted by the gills themselves."
Since the exhalation of air from any source is evidently as easily performed below the surface, the periodical ascent of the gars goes far to show that there is likewise an inhalation. But as it was not easy to determine this, on account of the small size of the young gars and the difficulty of handling the older ones, the writer experimented upon another Western Ganoid, the Amia, or "mud-fish," or "dog-fish."
When placed in a tank the Amia kept near the bottom, and seemed to prefer the darker portions. But it came to the surface at pretty regular intervals, emitting one or two large bubbles from the mouth, and, on descending, several smaller ones from the opercular orifice.
The fish was gradually accustomed to having the body gently embraced by the hand about the middle.
Fig. 4.—Vertical Longitudinal Section of the Head of Lepidosteus platystomus. One-half Natural Diameter.
Br, the brain cut on the median line so as to show the ventricles of the two hinder lobes, the cerebellum and optic lobes. SC, the spinal cord passing backward into the canal of the vertebral column (VC). CT. a mass of connective tissue filling the hinder part of the brain-cavity. HP. the right hypopharyngeal bone, just in front of the passage (CH) from the throat (Al) upward and backward into the air-bladder (A). Ve is a valve which seems to guard the opening from within; a corresponding valve is on the left side. LA is one of the openings from the median channel of the air-bladder into a lateral chamber. L is the liver, which terminates forward in a large blood-vessel, HV. A and V are the auricle and ventricle of the heart; BA, the branchial artery; and ba, the cut ends of the smaller arteries to the gills on the right side. T is the tongue.
Having been thus prepared, the fish was permitted to swim to and fro in the tank, but prevented from rising. It soon became uneasy, and, after a few not very violent efforts to disengage itself, emitted a large bubble of air.
Now, if this emission were all that was necessary we may suppose that it would have remained quiet for another period. On the contrary, after a second or two of repose (perhaps resulting from the habit of being satisfied after the respiratory act), the fish became more and more uneasy, moved rapidly to and fro, turned and twisted and lashed with its tail, and finally, by a violent effort, escaped from the hand. It rose to the surface, and, without emitting any bubble, opened its jaws widely and apparently gulped in a large volume of air. It then descended and remained quiet for the usual interval.
Fig. 5.—View from below of the Upper or Dorsal Wall of the Throat of the Long-nosed Gar (Lepidosteus osseus). One-half Natural Diameter.
The œsophagus is removed excepting that part of the dorsal wall (Al) which is closely attached to the air-bladder (A). Its cut edges are indicated by x x. Ch is the opening or "chink" leading into the air-bladder, and C C indicate projecting points at the sides of the chink. HP, hypopharyngeal bones armed with teeth.
The escaping air should be chemically examined. But, so far as the experiments go, it seems probable that, with both Amia and Lepldosteus, there occurs an inhalation as well as exhalation of air at pretty regular intervals, the whole process resembling that of the Menobranchus and other salamanders, and the tadpoles, which, as the gills shrink and the lungs increase, come more frequently to the surface for air.
But the reader may say: "These fishes have gills, of course; but have they also lungs?" To this the answer is both yes and no; for there are at least two different ways of interpreting certain facts; and some definitions are not as yet wholly agreed upon.
Fig. 6.—Cross-Section of the Air-Bladder of L osseus. One-half Natural Diameter.
The central open space is the median channel; on each side is seen one of the numerous subdivisions of the lateral portions of the air-bladder. Above are the median aorta and the two lateral veins, as in fig. 3.
The facts are as follows: the Lepidostens and Amia, like many other fishes, have an air-bladder—a sac lying under the spine and above the alimentary canal, and communicating by a slit-like orifice with the upper side of the throat. With sturgeons and catfishes and most common fishes, the sac is nearly or quite simple, and the communication with the throat may be very narrow or even closed Such fishes are not known to swallow air, and there is need of further information as to the composition and source of the contained gas. But the air-bladder of Amia and Lepidosteus is divided into many cells, so as to resemble a frog's lungs; and the walls and partitions of these cells have many blood-vessels. These air-bladders are, in fact, more cellular and more vascular than the lungs of Menobranchus, or the hinder and larger portion of the lungs of serpents. And, in the light of the observations already recorded, there seems good reason for believing that pure air is inhaled and vitiated air exhaled whenever the fish rises to the surface.
It is worth noting, also, that both Amia and Lepidosteus are very tenacious of life, and endure removal from the water for a time much better than do the sturgeons, whose air-bladders are neither cellular nor vascular. The latter, also, are bottom-feeders, while the gars seem to keep near the surface of the water.
Why, then, are not these air-bladders lungs?
The most obvious objection is, that their openings are into the upper or dorsal side of the throat, while the glottis of batrachians, reptiles, birds, quadrupeds, and ourselves, communicates with the lower or ventral side.
This objection may be met in two ways. In the first place, if allowed, we should have to admit that all the so-called air-breathing vertebrates have organs (the lungs) which have no representative in the fishes, and that most of the latter have an organ (the air-bladder) which has no representative in the former.
It is true that some fishes have no air-bladder; but with some, as Amphioxtis, the lamprey-eels, the sharks,[5] and the skates, we may infer that it has not yet become developed; while with others, as the flat fishes, the air-bladder may have been lost through what may be called a local retrograde metamorphosis.
It is important to note, also, that an air-bladder and lungs have never been found in one and the same animal; and since arms, front-legs, flippers, and wings, are all regarded as modifications of the same organs, anterior limbs; and since, in many other cases, organs of very different size, form, complexity, and function, are considered as homologous, we shall be following precedent in admitting a willingness to regard air-bladders and lungs as modifications of the same organ.
But the true argument against the objection is derived from the existence of transition forms, or links, between air-bladders and lungs, as to the position of the organs themselves, and their communications with the alimentary canal.
With Amia and Lepidosteus the air-bladder and the opening of the duct are both dorsal. With the Brazilian fish called Erythrinus (as first stated by Johannes Müller, and lately verified by the writer), the duct opens upon one side of the throat. In the lately-discovered Ceratodus of Australia, as described by Günther, the sac and duct are single, but the former is vascular, and the latter enters at the left of the ventral surface. With two African Ganoids, Polypterus and Calamoichthys (as also stated by Müller, and verified by the writer as to the latter genus) the sac is double, and communicates with the ventral side in the median line; but it is slightly cellular, as in Menobranchus.
Fig. 7.—Diagrams representing the Connection between the Air-bladder or Lung and the Alimentary Canal in Certain Vertebrates.
Al the alimentary canal, A, the air-bladder. AD. the air-duct.
The figures at the right show the alimentary canal and air-bladder from the left side; those at the left represent cross-sections more or less foreshortened in some cases.
A A′ represent the simple condition-connections of the air-bladder in the sturgeons (Acipenser) and in most Teleosts where the air duct remains open. B B′ represent the arrangement in Amia and Lepidosteus, where the duct opens upon the dorsal side of the throat, but the bladder is more or less cellular. The hinder end of the bladder is left open to indicate its great length in Lepidosteus. In C C′ is shown the arrangement in Erythrinus. The bladder is still upon the dorsal side, but the front part is separated from the hinder two-thirds by a constriction, and the long duct passes forward from just behind the constriction to enter the left side of the throat. There are fibrous partitions in part of the bladder, but I do not know that they are vascular. The condition in Ceratodus is shown at G; the bladder is single but vascular, and the duct opens on the ventral side, but not in the middle line.
In the remaining figures the air-duct opens on the lower or ventral surface of the throat, and the air-bladder is in two parts, which unite at the duct, but separate backward and lie upon the sides of the stomach, or even to some extent upon its dorsal surface next the back-bone. In the side-views only the left sac is seen; in the cross-sections the whole is fore-shortened so as to bring it into one plane. In Polypterus and Calamoichthys the inner surface of the sacs is nearly smooth, but in Lepidosiren, as in the salamanders, it is more or less folded and vascular, and is also connected with the heart by special vessels. In the reptiles, birds, and mammals, the duct or trachea soon divides into the two bronchial tubes.
Finally, in the "mudfishes" of Africa and South America (Protopterus and Lepidosiren) the duct is ventral, and the air-bladder is a double and lung-like sac with stiff walls.
This series seems to connect the air-bladder of the fishes with the lungs of the true aërial vertebrates, and to remove the objection based upon the different position of the communication between them and the alimentary canal.[6]
But another and perhaps more weighty objection has been urged by Prof. Huxley. He says: "But such air-sacs are air-bladders and not lungs, because they receive their blood from the adjacent arteries of the body, and not direct from the heart, while their efferent vessels are connected only with the veins of the general circulation."
According to this view, therefore, the Dipnoans (Protopterus and Lepidosiren) have lungs, because the blood goes to the air-sacs by a pulmonary artery, and returns by a pulmonary vein into a left auricle; while the cellular and vascular air-bladders of Amia and Lepdosteus are not lungs, because such an arrangement does not exist.
Yet Prof Huxley applies the name placenta to the vascular inter-digitations by which the young of some sharks are connected with the mother, although they are developed from the yolk and not, as in mammals, from the chorion. It would be interesting to know whether the nerves of the air-bladder are the same as those of the lungs.
The best test of the naturalness of the definition would be furnished by the discovery of some form having the pulmonary vessels connected with an air-bladder lying upon the dorsal side of the alimentary canal. Meantime, since all are agreed upon the facts, the question concerns interpretations and definitions.
Whether or not the air-bladder of the gar-pike is entitled to the name of lung, we may admit that it corresponds with a lung in its essential connection with the alimentary canal, and apparently in its function as an organ for aiding the oxygenation of the blood.
- ↑ These common names are very perplexing. Thus the true pike is Esox. The name dog-fish is popularly applied to Menobranchus, a batrachian; to Amia, a ganoid; and to Acanthias, a shark.
- ↑ A few examples have been taken in Cayuga Lake, in Central New York, having probably entered by the canal at its northern end; it is said to occur in the Susquehanna River, Pennsylvania. It is lately reported that a species has been found in China.
- ↑ Unwillingly, because all such assumptions are very undesirable. There have proved to be exceptions to nearly all general rules, whether of structure or of functions, as is shown in a paper by the writer, entitled "Is Nature inconsistent?"—(The Galaxy, April, 1876.)
- ↑ Although most other zoölogists have differed with Agassiz respecting the limits of the group, the name has been generally retained.
- ↑ Maclay has figured a rudimentary air-bladder in certain shark-embryos.
- ↑ In fact, considering the resemblance of the brains and enameled scales of Lepidosteus and Polypterus, and the differences of their air-bladders and ducts, one is inclined to regard the latter as of slight taxonomic importance.