FOOTNOTES:
[146] The cormorant is tamed for this purpose. A harness is placed about its wings and a ring about the lower part of its neck. Two or three birds may be driven by a boy in a shallow stream, a small net behind him to drive the fish down the river. In a large river like that of Gifu, where the cormorants are most used, the fishermen hold the birds from the boats and fish after dark by torchlight. The bird takes a great interest in the work, darts at the fishes with great eagerness, and fills its throat and gular pouch as far down as the ring. Then the boy takes him out of the water, holds him by the leg and shakes the fishes out into a basket. When the fishing is over the ayu are preserved, the ring is taken off from the bird's neck, and the zako or minnows are thrown to him for his share. These he devours greedily.
[CHAPTER XIX]
DISEASES OF FISHES
Contagious Diseases.—As compared with other animals the fishes of the sea are subject to but few specific diseases. Those in fresh waters, being more isolated, are more frequently attacked by contagious maladies. Often these diseases are very destructive. In an "epidemic" in Lake Mendota, near Madison, Wis., Professor Stephen A. Forbes reports a death of 300 tons of fishes in the lake. I have seen similar conditions among the land-locked alewife in Cayuga and Seneca Lakes, the dead fishes being piled on the beaches so as to fill the air with the stench of their decay.
Fig. 225.—Menhaden, Brevoortia tyrannus (Latrobe). Woods Hole, Mass.
Crustacean Parasites.—The external parasites of fishes are of little injury. These are mainly lernæans and other crustaceans (fish-lice) in the sea, and in the rivers different species of leeches. These may suck the blood of the fish, or in the case of certain crustaceans which lie under the tongue, steal the food as it passes along, as is done by Cymothoa prægustator, the "bug" of the mouth of the menhaden (Brevoortia tyrannus).
Fig. 226.—Australian Flying-fish, Exonautes unicolor (Valenciennes). Specimen from Tasman Sea, having parasitic lernæan crustaceans, to which parasitic barnacles are attached. (After Kellogg.)
The relation of this crustacean to its host suggested to Latrobe, its discoverer, the relation of the "foretaster" in Roman times to the tyrant whom he served. A similar commensation exists in the mouth of a mullet (Mugil hospes) at Panama. The writer has received, through the courtesy of Mr. A. P. Lundin, a specimen of a flying-fish (Exonautes unicolor) taken off Sydney, Australia. To this are attached three large copepod crustaceans of the genus Penella, the largest over two inches long, and to the copepods in turn are attached a number of barnacles (Conchoderma virgatum) so joined to the copepods as to suggest strange flowers, like orchids, growing out of the fish.
Fig. 227.—Black-nosed Dace, Rhinichthys atronasus (Mitchill). East Coy Creek, W. N. Y. Showing black spots of parasitic organisms. (From life by Mary Jordan Edwards.)
Myxosporidia, or Parasitic Protozoa.—Internal parasites are very numerous and varied. Some of them are bacteria, giving rise to infectious diseases, especially in ponds and lakes. Others are myxosporidia, or parasitic protozoans, which form warty appendages, which burst, discharging the germs and leaving ulcers in their place. In the report of the U. S. Fish Commissioner for 1892, Dr. R. R. Gurley has brought together our knowledge of the protozoans of the subclass Myxosporidia, to which these epidemics are chiefly due. These creatures belong to the class of Sporozoa, and are regarded as animals, their nearest relatives being the parasitic Gregarinida, from which they differ in having the germinal portion of the spore consisting of a single protoplasmic mass instead of falciform protoplasmic rods as in the worm-like Gregarines. The Myxosporidia are parasitic on fishes, both fresh-water and marine, especially beneath the epidermis of the gills and fins and in the gall-bladder and urinary bladder. In color these protozoa are always cream-white. In size and form they vary greatly. The cyst in which they lie is filled with creamy substance made up of spores and granule matter.
Dr. Gurley enumerates as hosts of these parasites about sixty species of fishes, marine and fresh-water, besides frogs, crustaceans, sea-worms, and even the crocodile. In the sharks and rays the parasites occur mainly in the gall-ducts, in the minnows within the gill cavity and epidermis, and in the higher fishes mainly but not exclusively in the same regions. Forty-seven species are regarded by Gurley as well defined. The diseases produced by them are very obscurely known. These parasites on American fishes have been extensively studied by Charles Wardall Stiles, Edwin Linton, Henry B. Ward, and others.
According to Dr. Linton the parasitism which results from infection with protozoan parasites will, of all kinds, be found to be the most important. Epidemics among European fish have been repeatedly traced to this source. The fatality which attends infection with psorosperms appears to be due to a secondary cause, however, namely, to bacilli which develop within the psorosperms (Myxobolus) tumors and give rise to ulceration. The discharge of these ulcers then disseminates the disease.
Fig. 228.—White Shiner, Notropis hudsonius (Clinton), with cysts of parasitic psorosperms. (After Gurley.)
"Brief mention of the remedies there proposed may appropriately be repeated here. Megnin sees no other method than to collect all the dead and sick fishes and to destroy them by fire. Ludwig thinks that the waters should be kept pure, and that the pollutions of the rivers by communities or industrial establishments should be interdicted. Further he says:
"That most dangerous contamination of the water by the Myxosporidia from the ulcers cannot of course be stopped entirely, but it is evident that it will be less if all fishermen are impressed with the importance of destroying all diseased and dead fish instead of throwing them back into the water. Such destruction must be so effected as to prevent the re-entry of the germs into the water.
"Railliet says that it is expedient to collect the diseased fish and to bury them at a certain depth and at a great distance from the water-course. He further states that this was done on the Meuse with success, so that at the end of some years the disease appeared to have left no trace."
Fig. 229.—White Catfish, Ameiurus catus (Linnæus), from Potomac River, infested by parasitic protozoa, Ichthyophthirus multifilis Fouquet. (After C. W. Stiles.)
Parasitic Worms: Trematodes.—Parasitic worms in great variety exist in the intestinal canal or in the liver or muscular substance of fishes.
Trematode worms are most common in fresh-water fishes. These usually are sources of little injury, especially when found in the intestines, but they may do considerable mischief when encysted within the body cavity or in the heart or liver. Dr. Linton describes 31 species of these worms from 25 different species of American fishes. In 20 species of fishes from the Great Lakes, 102 specimens, Dr. H. B. Ward found 95 specimens infected with parasites, securing 4000 trematodes, 2000 acanchocephala, 200 cestodes, and 200 nematodes. In the bowfin (Amia calva), trematodes existed in enormous numbers.
Cestodes.—Cestode worms exist largely in marine fishes, the adults, according to Dr. Linton, being especially common in the spiral valve of the shark. It is said that one species of human tape-worm (Bothriocephalus tænia) has been got from eating the flesh of the European tench (Tinca tinca).
The Worm of the Yellowstone.—The most remarkable case of parasitism of worms of this type is that given by the trout of Yellowstone Lake (Salmo clarki). This is thus described by Dr. Linton:
"One of the most interesting cases of parasitism in which direct injury results to the host, which has come to my attention, is that afforded by the trout of Yellowstone Lake (Salmo clarki). It was noticed by successive parties who visited the lake in connection with government surveys that the trout with which the lake abounded were, to a large extent, infested with a parasitic worm, which is most commonly in the abdominal cavity, in cysts, but which in time escapes from the cyst and tunnels into the flesh of its host. Fish, when thus much afflicted, are found to be lacking in vitality, weak, and often positively emaciated.
"It was my good fortune, in the summer of 1890, to visit this interesting region for the purpose of investigating the parasitism of the trout of Yellowstone Lake. The results of this special investigation were published in the Bulletin of the U. S. Fish Commission for 1889, vol. ix., pp. 337-358, under the title 'A Contribution to the Life-history of Dibothrium cordiceps, a Parasite Infesting the Trout of Yellowstone Lake.'
"I found the same parasite in the trout of Heart Lake, just across the great continental divide from Yellowstone Lake, but did not find any that had tunneled into the flesh of its host, while a considerable proportion of the trout taken in Yellowstone Lake had these worms in the flesh. Some of these worms were as much as 30 centimeters in length when first removed; others which had lain in water a few hours after removal before they were measured were much longer, as much as 54 centimeters. They are rather slender and of nearly uniform size throughout, 2.5 to 3 millimeters being an average breadth of the largest. I found the adult stage in the intestine of the large white pelican (Pelecanus erythrorhynchus), which is abundant on the lake and was found breeding on some small islands near the southern end of the lake.
"In the paper alluded to above I attempted to account for two things concerning this parasitism among the trout of Yellowstone Lake: First, the abundance of parasitized trout in the lake; second, the migration of the parasite into the muscular tissue of its host. The argument cannot be well summarized in as short space as the requirements of this paper demand. It is sufficient to say that what appear to me to be satisfactory explanations are supplied by the peculiar conditions of distribution of fish in the lakes of this national park. Until three or four years ago, when the U. S. Fish Commission stocked some of the lakes and streams of the park, the conditions with relation to fish life in the three principal lakes were as follows: Shoshone Lake, no fish of any kind; Heart Lake, at least three species, Salmo clarki, Leuciscus lineatus, and Catostomus ardens; Yellowstone Lake, one species, Salmo clarki. Shoshone and Yellowstone Lakes are separated from the river systems which drain them by falls too high for fish to scale. Heart Lake has no such barrier. The trout of Yellowstone Lake are confined to the lake and to eighteen miles of river above the falls. Whatever source of parasitism exists in the lake, therefore, must continue to affect the fish all their lives. They cannot be going and coming from the lake as the trout of Heart Lake may freely do. If their food should contain eggs of parasites, or if the waters in which they swim should contain eggs or embryos of parasites, they would be continually exposed to infection, with no chance for a vacation trip for recuperation. To quote from my report:
"'It follows, therefore, from the peculiar conditions surrounding the trout of Yellowstone Lake, that if there is a cause of parasitism present in successive years the trout are more liable to become infested than they would be in waters where they had a more varied range. Trout would become infested earlier and in greater relative numbers, and the life of the parasites themselves—that is, their residence as encysted worms—must be of longer duration than would be the rule where the natural conditions are less exceptional.... There are probably not less than one thousand pelicans on the lake the greater part of the time throughout the summer, of which at any time not less than 50 per cent. are infested with the adult form of the parasite, and, since they spend the greater part of their time on or over the water, disseminate millions of tape-worm eggs each in the waters of the lake. It is known that eggs of other dibothria hatch out in the water, where they swim about for some time, looking much like ciliated infusoria. Donnadieu found in his experiments on the adult dibothria of ducks that the eggs hatched out readily in warm water and very slowly in cold. If warm water, at least water that is warmer than the prevailing temperature of the lake, is needed for the proper development of these ova, the conditions are supplied in such places as the shore system of geysers and hot springs on the west arm of the lake, where for a distance of nearly three miles the shore is skirted by a hot spring and geyser formation, with numerous streams of hot water emptying into the lake, and large springs of hot water opening in the floor of the lake near shore.
"'Trout abound in the vicinity of these warm springs, presumably on account of the abundance of food there. They do not love the warm water, but usually avoid it. Several persons with whom I talked on the subject while in the park assert that diseased fish—that is to say, those which are thin and affected with flesh worms—are more commonly found near the warm water; that they take the bait readily but are logy. I frequently saw pelicans swimming near the shore in the vicinity of the warm springs on the west arm of the lake. It would appear that the badly infested or diseased fish, being less active and gamy than the healthy fish, would be more easily taken by their natural enemies, who would learn to look for them in places where they most abound. But any circumstances which cause the pelican and the trout to occupy the same neighborhood will multiply the chances of the parasites developing in both the intermediate and final host. The causes that make for the abundance of the trout parasite conspire to increase the number of adults. The two hosts react on each other and the parasite profits by the reaction. About the only enemies the trout had before tourists, ambitious to catch big strings of trout and photograph them with a kodak, began to frequent this region, were the fish-eating birds, and chief among these in numbers and voracity was the pelican. It is no wonder, therefore, that the trout should have become seriously parasitized. It may be inferred from the foregoing statements that the reason why the parasite of the trout of Yellowstone Lake migrates into the muscular tissue of its host must be found in the fact that the life of the parasite within the fish is much more prolonged than is the case where the conditions of life are less exceptional.
"The case just cited is probably the most signal one of direct injury to the host from the presence of parasites that I have seen. I shall enumerate more briefly a few additional cases out of a great number that I have encountered in my special investigations on the entozoa of fishes for the U. S. Fish Commission."
Many worms of this type abound in codfishes, bluefishes, striped bass, and other marine fishes, rendering them lean and unfit for food.
The Heart Lake Tape-worm.—Another very interesting case of parasitism is that of the large tape-worm (Ligula catostomi) infecting the suckers, Catostomus ardens, in the warm waters of Witch Creek, near Heart Lake, in the Yellowstone Park. Of this Dr. Linton gives the following account:
Fig. 230.—Sucker, Catostomus ardens (Jordan & Gilbert), from Heart Lake, Yellowstone Park, infested by a flatworm, Ligula catostomi Linton, itself probably a larva of Dibothrium. (After Linton.)
"In the autumn of 1889 Dr. David Starr Jordan found an interesting case of parasitism in some young suckers (Catostomus ardens) which he had collected in Witch Creek, a small stream which flows into Heart Lake, in the Yellowstone National Park. Specimens of these parasites were sent to me for identification. They proved to be a species of ligula, probably identical with the European Ligula simplicissima Rud., which is found in the abdominal cavity of the tench. On account of its larval condition in which it possesses few distinctive characters, I described it under the name Ligula catostomi. These parasites grow to a very large size when compared with the fish which harbors them, often filling the abdominal cavity to such a degree as to give the fish a deceptively plump appearance. The largest specimen in Dr. Jordan's collection measured, in alcohol, 28.5 centimeters in length, 8 millimeters in breadth at the anterior end, 11 millimeters at a distance of 7 millimeters from the anterior end, and 1.5 millimeters near the posterior end. The thickness throughout was about 2 millimeters. The weight of one fish was 9.1 grams, that of its three parasites 2.5 grams, or 27½ per cent. the weight of the host. If a man weighing 180 pounds were afflicted with tape-worms to a similar degree, he would be carrying about with him 50 pounds of parasitic impedimenta.
"In the summer of 1890 I collected specimens from the same locality. A specimen obtained from a fish 19 centimeters in length measured while living 39.5 centimeters in length and 15 millimeters in breadth at the anterior end. Another fish 15 centimeters in length harbored four parasites, 12, 13, 13, and 20 centimeters long, respectively, or 58 centimeters aggregate. Another fish 10 centimeters long was infested with a single parasite which was 39 centimeters in length.
"These parasites were found invariably free in the body cavity. Dr. Jordan's collections were made in October and mine in July of the following year. Donnadieu has found that this parasite most frequently attains its maximum development at the end of two years. It is probable, therefore, that Dr. Jordan and I collected from the same generation. Since these parasites, in this stage of their existence, develop, not by levying a toll on the food of their host, after the manner of intestinal parasites, but directly by the absorption of the serous fluid of their host, it is quite evident that they work a positive and direct injury. Since, however, they lie quietly in the body cavity of the fish and possess no hard parts to cause irritation, they work their mischief simply by the passive abstraction of the nutritive juices of their host, and by crowding the viscera into confined spaces and unnatural positions. The worms, in almost every case, had attained such a size that they far exceeded in bulk the entire viscera of their host.
"From the fact that the examples obtained were of comparatively the same age, it may be justly inferred that the period of infection to which the fish are subjected must be a short one. I did not discover the final host, but it is almost certain to be one or more of the fish-eating species of birds which visit that region, and presumably one of which, in its migrations, pays but a brief visit to this particular locality. This parasite was found only in the young suckers which inhabit a warm tributary of Witch Creek. They were not found in the large suckers of the lake. These young Catostomi were found in a single school, associated with the young of the chub (Leuciscus lineatus), in a stream whose temperature was 95° F. near where it joined a cold mountain brook whose temperature was 46° F. We seined several hundred of these young suckers and chubs, ranging in length from 6 to 19 centimeters. The larger suckers were nearly all infested with these parasites, the smaller ones not so much, and the smallest scarcely at all. Or, to give concrete examples: Of 30 fish ranging in length from 14 to 19 centimeters, only one or two were without parasites; of 45 specimens averaging about 10 centimeters in length, 15 were infested and 30 were not; of 65 specimens averaging about 9 centimeters in length, 10 were infested and 55 were not; of 62 specimens less than 9 centimeters in length, 2 were infested and 60 were not. None of the chubs were infested with this parasite.
"The conditions under which these fish were found are worthy of passing notice. The stream which they occupied flowed with rather sluggish current into a swift mountain stream, which it met almost at right angles. The school of young chubs and suckers showed no inclination to enter the cold water, even to escape the seine, but would dart around the edge of the seine, in the narrow space between it and the bank, in preference, apparently, to taking to the colder water. When not disturbed by the seine they would swim up near to the line which marked the division between the cold and the warm water, and seemed to be gazing with open mouth and eyes at the trout which occasionally darted past in the cold stream. The trout appeared to avoid the warm water, while the chubs and suckers appeared to avoid the cold water. It may be that what the latter really avoided was the special preserve of the trout, since large chubs and suckers are found in abundance in the lake, which is quite cold, a temperature of 40° F. having been taken by us at a depth of 124 feet.
"Since the eggs of this parasite, after the analogy of closely related forms, in all probability are discharged into the water from the final host and hatch out readily in warm water, where they may live for a longer or shorter time as free-swimming planula-like forms, it will be observed that the sluggish current and high temperature of the water in which these parasitized fish occur give rise to conditions which are highly favorable to infection.
"It may be of passing interest to state here what I have recorded elsewhere, that ligulæ, probably specifically identical with L. catostomi, form an article of food in Italy, where they are sold in the markets under the name maccaroni piatti; also in southern France, where they are less euphemistically but more truthfully called the ver blanc. So far as my information goes, this diet of worms is strictly European.
"It is not necessary to prove cases of direct injury resulting from the presence of parasites in order to make out a case against them. In the sharp competition which nature forces on fishes in the ordinary struggle for existence, any factor which imparts an increment either of strength or of weakness may be a very potent one, and in a long term of years may determine the relative abundance or rarity of the individuals of a species. In most cases the interrelations between parasite and host have become so adjusted that the evil wrought by the parasite on its host is small. Parasitic forms, like free forms, are simply developing along the lines of their being, but unlike most free forms they do not contribute a fair share to the food of other creatures."
Thorn-head Worms.—The thorn-head worms called Acanthocephala are found occasionally in large numbers in different kinds of fishes. They penetrate the coats of the intestines, producing much irritation and finally waxy degeneration of the tissues.
According to Linton, there is probably no practical way of counteracting the bad influences of worms of this order, since their larval state is passed, in some cases certainly, and in most cases probably, in small crustacea, which constitute a constant and necessary source of food for the fish. The same remark which was made in another connection with regard to the disposal of the viscera of fish applies here. In no case should the viscera of fish be thrown back into the water. In this order the sexes are distinct, and the females become at last veritable sacs for the shelter and nourishment of enormous numbers of embryos. The importance, therefore, of arresting the development of as many embryos as possible is at once apparent.
Nematodes.—The round worms or nematodes are very especially abundant in marine fishes, and particularly in the young. The study of these forms has a large importance to man. Dr. Linton pertinently observes:
"Where there is exhaustive knowledge of the thing itself the application of that knowledge toward getting good out of it or averting evil that may come from it first becomes possible. For example, a knowledge of the life-history of Trichina spiralis and its pathological effects on its host has taught people a simple way of securing immunity from its often deadly effects. A knowledge of the life-histories of the various species of tæniæ which infest man and the domestic animals, frequently to their serious hurt, has made it possible to diminish their numbers, and may, in time, lead to their practical extinction.
"So with the parasites of fishes. Whenever for any reason or reasons parasitism of any sort becomes so prevalent with any species as to amount to a disease, the remedy will be suggested, and in some cases may be practically applied. If, for example, it were thought desirable to counteract the influences which are at work to cause the parasitism of the trout of Yellowstone Lake, it could be very largely accomplished by breaking up the breeding-places of the pelican on the islands of the lake. With regard to parasitism among the marine food-fishes, the remedy while plainly suggested by the circumstances, might be difficult of application. Yet something could be done even there, if it were thought necessary to lessen the amount of parasitism. If such precautions as the destruction of the parasites which abound in the viscera of fish before throwing them back into the water, and if no opportunity be lost of killing those sharks which feed on the food-fishes, two sources of the prevalence of parasites would be affected and the sum total of parasitism diminished. These remarks are made not so much because such precautions are needed as to suggest possible applications of knowledge which is already available."
Parasitic Fungi.—Fishes are often subject to wounds. If not too serious these will heal in time, with or without scars. Some lost portions may be restored, but not those including bone fin-rays or scales. In the fresh waters, wounds are usually attacked by species of fungus, notably Saprolegnia ferox, Saprolegnia mixta, and others, which makes a whitish fringe over a sore and usually causes death. This fungus is especially destructive in aquaria. This fungus is not primarily parasitic, but it fixes itself in the slime of a fish or in an injured place, and once established the animal is at its mercy. Spent salmon are very often attacked by this fungus. In America the spent salmon always dies, but in Scotland, where such is not the case, much study has been given to this plant and the means by which it may be exterminated. Dr. G. P. Clinton gives a useful account of the development of Saprolegnia, from which we take the following:
"The minute structure and life-history of such fungous forms have been so thoroughly made out by eminent specialists that no investigation along this line was made, save to observe those phenomena which might be easily seen with ordinary microscopic manipulations. The fungus consists of branched, hyaline filaments, without septa, except as these are found cutting off the reproductive parts of the threads. It is made up of a root-like or rhizoid part that penetrates the fish and a vegetative and reproductive part that radiates from the host. The former consists of branched tapering threads which pierce the tissues for a short distance, but are easily pulled out. The function of this part is to obtain nourishment for the growth of the external parts. Prostrate threads are found running through the natural slime covering the fish, and from these are produced the erect radiating hyphæ so plainly seen when in the water. The development of these threads appears to be very rapid when viewed under the microscope, although the growth made under favorable conditions in two days is only about a third of an inch. From actual measurements of filaments of the fungus placed in water and watched under the microscope, it was found that certain threads made a growth of about 3000 microns in an hour. Two others, watched for twenty minutes, gave in that time a growth of 90 and 47 microns respectively; and yet another filament, observed during two periods of five minutes each, made a growth of 28 microns each time. In ordinary cultures the rate of growth depends upon the condition of the medium, host, etc."
Fig. 231.—Quinnat Salmon, Oncorhynchus tschawytscha (Walbaum). Monterey Bay. (Photograph by C. Rutter.)
Professor H. A. Surface thus speaks of the attacks of Saprolegnia on the lamprey:
"The attack that attends the end of more lampreys than does any other is that of the fungus (Saprolegnia sp.). This looks like a gray slime and eats into the exterior parts of the animal, finally causing death. It covers the skin, the fins, the eyes, the gill-pouches, and all parts, like leprosy. It starts where the lamprey has been scratched or injured or where its mate has held it, and develops very rapidly when the water is warm. It is found late in the season on all lampreys that have spawned out, and it is almost sure to prove fatal, as we have repeatedly seen with attacked fishes or lampreys kept in tanks or aquaria. With choice aquarium fishes a remedy, or at least a palliative, is to be found in immersion in salt water for a few minutes or in bathing the affected parts with listerine. Since these creatures complete the spawning process before the fungoid attack proves serious to the individual, it can be seen that it affects no injury to the race, as the fertilized eggs are left to come to maturity. Also, as it is nature's plan that the adult lampreys die after spawning once, we are convinced that death would ensue without the attack of the fungus; and in fact this is to be regarded as a resultant of those causes that produce death rather than the immediate cause of it. Its only natural remedy is to be found in the depths of the lake (450 feet) where there is a uniform or constant temperature of about 39° Fahr., and where the light of the noon-day sun penetrates with an intensity only about equal to starlight on land on a clear but moonless night.
Fig. 232.—Young Male Quinnat Salmon, Oncorhynchus tschawytscha, dying after spawning. Sacramento River. (Photograph by Cloudsley Rutter.)
"As light and heat are essential to the development of the fungus, which is a plant growth and properly called a water mold, and as their intensity is so greatly diminished in the depth of the lake, it is probable that if creatures thus attacked should reach this depth they might here find relief if their physical condition were otherwise strong enough to recuperate. However, we have recently observed a distinct tendency on the part of fungus-covered fishes to keep in the shallower, and consequently warmer, parts of the water, and this of course results in the more rapid growth of the sarcophytic plant, and the death of the fishes is thus hastened.
"All kinds of fishes and fish-eggs are subject to the attacks of such fungus, especially after having been even slightly scratched or injured. As a consequence, the lamprey attacks on fishes cause wounds that often become the seat of a slowly spreading but fatal fungus. We have seen many nests of the bullhead, or horned pout (Ameiurus nebulosus), with all the eggs thus destroyed, and we have found scores of fishes of various kinds thus killed or dying. It is well known that in many rivers this is the apparent cause of great mortality among adult salmon. Yet we really doubt if it ever attacks uninjured fishes that are in good strong physical condition which have not at least had the slime rubbed from them when captured. It is contagious, not only being conveyed from one infested fish to another, but from dead flies to fishes." (For a further discussion of this subject see an interesting and valuable Manual of Fish Culture, by the U. S. Fish Commission, 1897.)
Earthquakes.—Occasionally an earthquake has been known to kill sea-fishes in large numbers. The Albatross obtained specimens of Sternoptyx diaphana in the Japanese Kuro Shiwo, killed by the earthquakes of 1896, which destroyed fishing villages of the coast of Rikuchu in northern Japan.
Mortality of Tilefish.—Some years ago in the Gulf Stream off Newfoundland an immense mortality of the filefish (Lopholatilus chamæleonticeps) was reported by fishermen. This handsome and large fish, inhabiting deep waters, died by thousands. For this mortality, which almost exterminated the species, no adequate cause has been found.
As to the destruction of fresh-water fishes by larger enemies, we may quote from Professor H. A. Surface. He says there is no doubt that these three species, the lake lamprey (Petromyzon marinus unicolor), the garpike (Lepidosteus osseus), and the mud-puppy (Necturus maculosus), named "in order of destructiveness, are the three most serious enemies of fishes in the interior of this State [New York], each of which surely destroys more fishes annually than are caught by all the fishermen combined. The next important enemies of fishes in order of destructiveness, according to our observations and belief, are spawn-eating fishes, water-snakes, carnivorous or predaceous aquatic insects (especially larvæ), and piscivorous fishes and birds." The lamprey attaches itself to larger fishes, rasping away their flesh and sucking their blood, as shown in the accompanying plate.
Fig. 233.—Catfishes, Ameiurus nebulosus Le Sueur, destroyed by lampreys (Petromyzon marinus unicolor De Kay). Cayuga Lake, N. Y. (Modified from photograph by Prof. H. A. Surface.)
[CHAPTER XX]
THE MYTHOLOGY OF FISHES
The Mermaid.—A word may be said of the fishes which have no existence in fact and yet appear in popular literature or in superstition.
The mermaid, half woman and half fish, has been one of the most tenacious among these, and the manufacture of their dried bodies from the head, shoulders, and ribs of a monkey sealed to the body of a fish has long been a profitable industry in the Orient. The sea-lion, the dugong, and other marine mammals have been mistaken for mermaids, for their faces seen at a distance and their movements at rest are not inhuman, and their limbs and movements in the water are fish-like.
In China, small mermaids are very often made and sold to the curious. The head and torso of a monkey are fastened ingeniously to the body and tail of a fish. It is said that Linnæus was once forced to leave a town in Holland for questioning the genuineness of one of these mermaids, the property of some high official. These monsters are still manufactured for the "curio-trade."
The Monkfish.—Many strange fishes were described in the Middle Ages, the interest usually centering in some supposed relation of their appearance with the affairs of men. Some of these find their way into Rondelet's excellent book, "Histoire Entière des Poissons," in 1558. Two of these with the accompanying plate of one we here reproduce. Other myths less interesting grew out of careless, misprinted, or confused accounts on the part of naturalists and travelers.
"In our times in Norway a sea-monster has been taken after a great storm, to which all that saw it at once gave the name of monk; for it had a man's face, rude and ungracious, the head shorn and smooth. On the shoulders, like the cloak of a monk, were two long fins instead of arms, and the end of the body was finished by a long tail. The picture I present was given me by the very illustrious lady, Margaret de Valois, Queen of Navarre, who received it from a gentleman who gave a similar one to the emperor, Charles V., then in Spain. This gentleman said that he had seen the monster as the portrait shows it in Norway, thrown by the waves and tempests on the beach at a place called Dieze, near the town called Denelopoch. I have seen a similar picture at Rome not differing in mien. Among the sea-beasts, Pliny mentions a sea-mare and a Triton as among the creatures not imaginary. Pausanias also mentions a Triton."
Fig. 234.—"Le monstre marin an habit de Moine." (After Rondelet.)
Rondelet further says:
The Bishop-fish.—"I have seen a portrait of another sea-monster at Rome, whither it had been sent with letters that affirmed for certain that in 1531 one had seen this monster in a bishop's garb, as here portrayed, in Poland. Carried to the king of that country, it made certain signs that it had a great desire to return to the sea. Being taken thither it threw itself instantly into the water."
Fig. 235.—"Le monstre marin en habit d'Évêque." (After Rondelet.)
The Sea-serpent.—A myth of especial persistency is that of the sea-serpent. Most of the stories of this creature are seaman's yarns, sometimes based on a fragment of wreck, a long strip of kelp, the power of suggestion or the incitement of alcohol. But certain of these tales relate to real fishes. The sea-serpent with an uprearing red mane like that of a horse is the oarfish (Regalecus), a long, slender, fragile fish compressed like a ribbon and reaching a length of 25 feet. We here present a photograph of an oarfish (Regalecus russelli) stranded on the California coast at Newport in Orange County, California. A figure of a European species (Regalecus glesne) is also given showing the fish in its uninjured condition. Another reputed sea-serpent is the frilled shark (Chlamydoselachus angineus), which has been occasionally noticed by seamen. The struggles of the great killer (Orca orca) with the whales it attacks and destroys has also given rise to stories of the whale struggling in the embrace of some huge sea-monster. This description is correct, but the mammal is a monster itself, a relative of the whale and not a reptile.
Fig. 236.—Oarfish, Regalecus russelli, on the beach at Newport, Orange Co., Cal. (Photograph by C. P. Remsberg.)
Fig. 237.—Glesnæs Oarfish, Regalecus glesne Ascanius. Newcastle, England. (After Day.)
It is often hard to account for some of the stories of the sea-serpent. A gentleman of unquestioned intelligence and sincerity lately described to the writer a sea-serpent he had seen at short range, 100 feet long, swimming at the surface, and with a head as large as a barrel. I do not know what he saw, but I do know that memory sometimes plays strange freaks.
Little venomous snakes with flattened tails (Platyurus, Pelamis) are found in the salt bays in many tropical regions of the Pacific (Gulf of California, Panama, East Indies, Japan), but these are not the conventional sea-serpents.
Certain slender fishes, as the thread-eel (Nemichthys) and the wolf-eel (Anarrhichthys), have been brought to naturalists as young sea-serpents, but these of course are genuine fishes.
Whatever the nature of the sea-serpent may be, this much is certain, that while many may be seen, none will ever be caught. The great swimming reptiles of the sea vanished at the end of Mesozoic time, and as living creatures will never be known of man.
As a record of the Mythology of Science, we may add the following remarks of Rafinesque on the imaginary garpike (Litholepis adamantinus), of which a specimen was painted for him by the wonderful brush of Audubon:
"This fish may be reckoned the wonder of the Ohio. It is only found as far up as the falls, and probably lives also in the Mississippi. I have seen it, but only at a distance, and have been shown some of its singular scales. Wonderful stories are related concerning this fish, but I have principally relied upon the description and picture given me by Mr. Audubon. Its length is from 4 to 10 feet. One was caught which weighed 400 pounds. It lies sometimes asleep or motionless on the surface of the water, and may be mistaken for a log or snag. It is impossible to take it in any other way than with the seine or a very strong hook; the prongs of the gig cannot pierce the scales, which are as hard as flint, and even proof against lead balls! Its flesh is not good to eat. It is a voracious fish. Its vulgar names are diamond-fish (owing to its scales being cut like diamonds), devil-fish, jackfish, garjack, etc. The snout is large, convex above, very obtuse, the eyes small and black; nostrils small, round before the eyes; mouth beneath the eyes, transversal with large angular teeth. Pectoral and abdominal fins trapezoidal. Dorsal and anal fins equal, longitudinal, with many rays. The whole body covered with large stone scales, lying in oblique rows; they are conical, pentagonal pentædral, with equal sides, from half an inch to one inch in diameter, brown at first but becoming the color of turtle-shell when dry. They strike fire with steel and are ball-proof!"
Fig. 238.—Thread-eel, Nemichthys avocetta Jordan & Gilbert. Puget Sound.
[CHAPTER XXI]
CLASSIFICATION OF FISHES
Taxonomy.—Classification, as Dr. Elliott Coues has well said,[147] is a natural function of "the mind which always strives to make orderly disposition of its knowledge and so to discover the reciprocal relations and interdependencies of the things it knows. Classification presupposes that there do exist such relations, according to which we may arrange objects in the manner which facilitates their comprehension, by bringing together what is like and separating what is unlike, and that such relations are the result of fixed inevitable law. It is therefore taxonomy (τάξις, away; νόμος, law) or the rational, lawful disposition of observed facts."
A perfect taxonomy is one which would perfectly express all the facts in the evolution and development of the various forms. It would recognize all the evidence from the three ancestral documents, palæontology, morphology, and ontogeny. It would consider structure and form independently of adaptive or physiological or environmental modifications. It would regard as most important those characters which had existed longest unchanged in the history of the species or type. It would regard as of first rank those characters which appear first in the history of the embryo. It would regard as of minor importance those which had arisen recently in response to natural selection or the forced alteration through pressure of environment, while fundamental alterations as they appear one after another in geologic time would make the basal characters of corresponding groups in taxonomy. In a perfect taxonomy or natural system of classification animals would not be divided into groups nor ranged in linear series. We should imagine series variously and divergently branched, with each group at its earlier or lower end passing insensibly into the main or primitive stock. A very little alteration now and then in some structure is epoch-making, and paves the way through specialization to a new class or order. But each class or order through its lowest types is interlocked with some earlier and otherwise diverging group.
Defects in Taxonomy.—A sound system of taxonomy of fishes should be an exact record of the history of their evolution. But in the limitations of book-making, this transcript must be made on a flat page, in linear series, while for centuries and perhaps forever whole chapters must be left vacant and others dotted everywhere with marks of doubt. For science demands that positive assertion should not go where certainty cannot follow. A perfect taxonomy of fishes would be only possible through the study, by some Artedi, Müller, Cuvier, Agassiz, Traquair, Gill, or Woodward, of all the structures of all the fishes which have ever lived. There are many fishes living in the sea which are not yet known to any naturalist, many others are known from one or two specimens, but not yet accessible to students in other continents. Many are known externally from specimens in bottles or drawings in books, but have not been studied thoroughly by any one, and the vast multitude of species have perished in Palæozoic, Mesozoic, and Tertiary seas without leaving a tooth or bone or fin behind them. With all this goes human fallibility, the marring of our records, such as they are, by carelessness, prejudice, dependence, and error. Chief among these defects are the constant mistaking of analogy for homology, and the inability of men to trust their own eyes as against the opinion of the greater men who have had to form their opinions before all evidence was in. Because of these defects, the current system of classification is always changing with each accession of knowledge.
The result is, again to quote from Dr. Coues, "that the natural classification, like the elixir of life or the philosopher's stone, is a goal far distant."
Analogy and Homology.—Analogy, says Dr. Coues, "is the apparent resemblance between things really unlike—as the wing of a bird and the wing of a butterfly, as the lungs of a bird and the gills of a fish. Homology is the real resemblance, or true relation between things, however different they may appear to be—as the wing of a bird and the foreleg of a horse, the lungs of a bird and the swim-bladder of a fish. The former commonly rests upon mere functional, i.e. physiological, modifications; the latter is grounded upon structural, i.e., morphological, identity or unity. Analogy is the correlative of physiology, homology of morphology; but the two may be coincident, as when structures identical in morphology are used for the same purposes, and are therefore physiologically identical. Physiological diversity of structure is incessant, and continually interferes with morphological identity of structure, to obscure or obliterate the indications of affinity the latter would otherwise express clearly.... We must be on our guard against those physiological appearances which are proverbially deceptive!"
"It is possible and conceivable that every animal should have been constructed upon a plan of its own, having no resemblance whatever to the plan of any other animal. For any reason we can discover to the contrary, that combination of natural forces which we term life might have resulted from, or been manifested by, a series of infinitely diverse structures; nor would anything in the nature of the case lead us to suspect a community of organization between animals so different in habit and in appearance as a porpoise and a gazelle, an eagle and a crocodile, or a butterfly and a lobster. Had animals been thus independently organized, each working out its life by a mechanism peculiar to itself, such a classification as that now under contemplation would be obviously impossible; a morphological or structural classification plainly implying morphological or structural resemblances in the things classified.
"As a matter of fact, however, no such mutual independence of animal forms exists in nature. On the contrary, the members of the animal kingdom, from the highest to the lowest, are marvelously connected. Every animal has something in common with all its fellows—much with many of them, more with a few, and usually so much with several that it differs but little from them.
"Now, a morphological classification is a statement of these gradations of likeness which are observable in animal structures, and its objects and uses are manifold. In the first place, it strives to throw our knowledge of the facts which underlie, and are the cause of, the similarities discerned into the fewest possible general propositions, subordinated to one another, according to their greater or less degree of generality; and in this way it answers the purpose of a memoria technica, without which the mind would be incompetent to grasp and retain the multifarious details of anatomical science."
Coues on Classification.—It is obvious that fishes like other animals may be classified in numberless ways, and as a matter of fact by numberless men they have been classified in all sorts of fashions. "Systems," again quoting from Dr. Coues, "have been based on this and that set of characters and erected from this or that preconception in the mind of the systematist.... The mental point of view was that every species of bird (or of fish) was a separate creature, and as much of a fixture in nature's museum as any specimen in a naturalist's cabinet. Crops of classifications have been sown in the fruitful soil of such blind error, but no lasting harvest has been reaped.... The genius of modern taxonomy seems to be so certainly right, to be tending so surely even if slowly in the direction of the desired consummation, that all differences of opinion we hope will soon be settled, and defect of knowledge, not perversity of mind, is the only obstacle in the way of success. The taxonomic goal is not now to find the way in which birds (or other animals) may be most conveniently arranged, but to discover their pedigree, and so construct their family tree. Such a genealogical table, or phylum (φῦλον, tribe, race, stock), as it is called, is rightly considered the only taxonomy worthy the name—the only true or natural classification. In attempting this end, we proceed upon the belief that, as explained above, all birds, like all other animals and plants, are related to each other genetically, as offspring are to parents, and that to discover their generic relations is to bring out their true affinities—in other words, to reconstruct the actual taxonomy of nature. In this view there can be but one 'natural' classification, to the perfecting of which all increase in our knowledge of the structure of birds infallibly and inevitably tends. The classification now in use or coming into use is the result of our best endeavors to accomplish this purpose, and represents what approach we have made to this end. It is one of the great corollaries of that theorem of evolution which most naturalists are satisfied has been demonstrated. It is necessarily a morphological classification; that is, one based solely upon considerations of structure or form (μορφή, form, morphe), and for the following reasons: Every offspring tends to take on precisely the form or structure of its parents, as its natural physical heritage; and the principle involved, or the law of heredity, would, if nothing interfered, keep the descendants perfectly true to the physical characters of their progenitors; they would 'breed true' and be exactly alike. But counter influences are incessantly operative, in consequence of constantly varying external conditions of environment; the plasticity of organization of all creatures rendering them more or less susceptible of modifications by such means, they become unlike their ancestors in various ways and to different degrees. On a large scale is thus accomplished, by natural selection and other natural agencies, just what man does in a small way in producing and maintaining different breeds of domestic animals. Obviously, amidst such ceaselessly shifting scenes, degrees of likeness or unlikeness of physical structure indicate with the greatest exactitude the nearness or remoteness of organisms in kinship. Morphological characters derived from the examination of structure are therefore the surest guides we can have to the blood relationships we desire to establish; and such relationships are the 'natural affinities' which all classification aims to discover and formulate."
Species as Twigs of a Genealogical Tree.—In another essay Dr. Coues has compared species of animals to "the twigs of a tree separated from the parent stem. We name and arrange them arbitrarily in default of a means of reconstructing the whole tree according to nature's ramifications." If one had a tree, all in fragments, pieces of twig and stem, some of them lost, some destroyed, and some not yet separated from the mass not yet picked over, and wished to place each part where he could find it, he would be forced to adopt some system of natural classification. In such a scheme he would lay those parts together which grew from the same branch. If he were compelled to arrange all the fragments in a linear series, he would place together those of one branch, and when these were finished he would begin with another. If all this were a matter of great importance and extending over years or over many lifetimes, with many errors to be made and corrected, a set of names would be adopted—for the main trunk, for the chief branches, the lesser branches, and on down to the twigs and buds.
A task of this sort on a world-wide scale is the problem of systematic zoology. There is reason to believe that all animals and plants sprang from a single stock. There is reasonable certainty that all vertebrate animals are derived from a single origin. These vertebrate animals stand related to each other, like the twigs of a gigantic tree of which the lowermost branches are the aquatic forms to which we give the name of fishes. The fishes are here regarded as composed of six classes or larger lines of descent. Each of these, again, is composed of minor divisions called orders. The different species or ultimate kinds of animals are grouped in genera. A genus is an assemblage of closely related species grouped around a central species as type. The type of a genus is, in common usage, that species with which the name of the genus was first associated. The name of the genus as a noun, often with that of the species which is an adjective in signification if not in form, constitutes the scientific name of the species. Thus Petromyzon is the genus of the common large lamprey, marinus is its species, and the scientific name of the species is Petromyzon marinus. Petromyzon means stone-sucker; marinus, of the sea, thus distinguishing it from a species called fluviatilis, of the river. In like fashion all animals and plants are named in scientific record or taxonomy. Technical names are necessary because vernacular names fail. Half a million kinds of animals are known, while not half a thousand vernacular names exist in any language. And these are always loosely used, half a dozen of them often for the same species, one name often for a dozen species.
In the same way, whenever we undertake an exact description, we must use names especially devised for that purpose. We cannot use the same names for the bones of the head of a fish and those of the head of a man, for a fish has a different series of bones, and this series is different with different fishes.
Nomenclature.—A family in zoology is an assemblage of related genera. The name of a family, for convenience, always ends in the patronymic idæ, and it is always derived from the leading genus, that is, the one best known or earliest studied. Thus all lampreys constitute the family Petromyzonidæ. An order may contain one or more families. An order is a division of a larger group; a family an assemblage of related smaller groups. Intermediate groups are often recognized by the prefixes sub or super. A subgenus is a division of a genus. A subspecies is a geographic race or variation within a species; a super-family a group of allied families. Binomial nomenclature, or the use of the name of genus and species as a scientific name, was introduced into science as a systematic method by Linnæus. In the tenth edition of his Systema Naturæ, published in 1758, this method was first consistently applied to animals. By common consent the scientific naming of animals begins with this year, and no account is taken of names given earlier, as these are, except by accident, never binomial. Those authors who wrote before the adoption of the rule of binomials and those who neglected it are alike "ruled out of court." The idea of genus and species was well understood before Linnæus, but the specific name used was not one word but a descriptive phrase, and this phrase was changed at the whim of the different authors.
Fig. 239.—Horned Trunkfish, Cowfish, or Cuckold, Lactophrys tricornis (Linnæus). Charleston, S. C.
Nomenclature of Trunkfishes.—Examples of such names are those of the West Indian trunkfish, or cuckold (Ostracion tricorne, Linnæus). Lister refers to a specimen in 1686 as "Piscis triangularis capiti cornutu cui e media cauda cutanea aculeus longus erigitus." This Artedi alters in 1738 to Ostracion triangulatus aculeis duobus in capite et unico longiore superne ad caudam. This is more accurately descriptive and it recognizes the existence of a generic type, Ostracion, or trunkfish, to cover all similar fishes. French writers transformed this into various phrases beginning "Coffre triangulaire à trois cornes," or some similar descriptive epithet, and in English or German it was likely to wander still farther from the original. But Linnæus condenses it all in the word tricornis, which, although not fully descriptive, is still a name which all future observers can use and recognize.
It is true that common consent fixes the date of the beginning of nomenclature at 1758. But to this there are many exceptions. Some writers date genera from the first recognition of a collective idea under a single name. Others follow even species back through the occasional accidental binomials. Most British writers have chosen the final and completed edition of the Systema Naturæ, the last work of Linnæus, in 1766, in preference to the earlier volume. But all things considered, justice and convenience alike seem best served by the use of the edition of 1758.
Synonymy and Priority.—Synonymy is the record of the names applied at different times to the same group or species. With characteristic pungency Dr. Coues defines synonymy as "a burden and a disgrace to science." It has been found that the only way to prevent utter confusion is to use for each genus or species the first name applied to it and no other. The first name, once properly given, is sacred because it is the right name. All other later names whatever their appropriateness are wrong names. In science, of necessity, a name is a name without any necessary signification. For this reason and for the further avoidance of confusion, it remains as it was originally spelled by the author, obvious misprints aside, regardless of all possible errors in classical form or meaning. The names in use are properly written in Latin or in Latinized Greek, the Greek forms being usually preferred as generic names, the Latin adjectives for names of species. Many species are named in honor of individuals, these names being usually given the termination of the Latin genitive, as Sebastodes gillii, Liparis agassizi. In recent custom all specific names are written with the small initial; all generic names with the capital.
One class of exceptions must be made to the law of priority. No generic name can be used twice among animals, and no specific name twice in the same genus. Thus the name Diabasis has to be set aside in favor of the next name Hæmulon, because Diabasis was earlier used for a genus of beetles. The specific name Pristipoma humile is abandoned, because there was already a humile in the genus Pristipoma.
The Conception of Genus.—In the system of Linnæus, a genus corresponds roughly to the modern conception of a family. Most of the primitive genera contained a great variety of forms, as well as usually some species belonging to other groups disassociated from their real relationships.
As greater numbers of species have become known the earlier genera have undergone subdivision until in the modern systems almost any structural character not subject to intergradation and capable of exact definition is held to distinguish a genus. As the views of these characters are undergoing constant change, and as different writers look upon them from different points of view, or with different ideas of convenience, we have constant changes in the boundaries of genera. This brings constant changes in the scientific names, although the same specific name should be used whatever the generic name to which it may be attached. We may illustrate these changes and the burden of synonymy as well by a concrete example.
The Trunkfishes.—The horned trunkfish, or cuckold, of the West Indies was first recorded by Lister in 1686, in the descriptive phrase above quoted. Artedi, in 1738, recognized that it belonged with other trunkfishes in a group he called Ostracion. This, to be strictly classic, he should have written Ostracium, but he preferred a partly Greek form to the Latin one. In the Nagg's Head Inn in London, Artedi saw a trunkfish he thought different, having two spines under the tail, while Lister's figure seemed to show one spine above. This Nagg's Head specimen Artedi called "Ostracion triangulatus duobus aculeis in fronte et totidem in imo ventre subcaudalesque binis."
Next came Linnæus, 1758, who named Lister's figure and the species it represented, Ostracion tricornis, which should in strictness have been Ostracion tricorne, as ὀστρακίον, a little box, is a neuter diminutive. The Nagg's Head fish he named Ostracion quadricornis. The right name now is Ostracion tricornis, because the name tricornis stands first on the page in Linnæus' work, but Ostracion quadricornis has been more often used by subsequent authors because it is more truthful as a descriptive phrase. In 1798, Lacépède changed the name of Lister's fish to Ostracion listeri, a needless alteration which could only make confusion.
Fig. 240.—Horned Trunkfish, Ostracion cornutum Linnæus. East Indies. (After Bleeker.)
In 1818, Dr. Samuel Latham Mitchill, receiving a specimen from below New Orleans, thought it different from tricornis and quadricornis and called it Ostracion sexcornutus; Dr. Holard, of Paris, in 1857, named a specimen Ostracion maculatus, and at about the same time Bleeker named two others from Africa which seem to be the same thing, Ostracion guineensis and Ostracion gronovii. Lastly, Poey calls a specimen from Cuba Acanthostracion polygonius, thinking it different from all the rest, which it may be, although my own judgment is otherwise. This brings up the question of the generic name. Among trunkfishes there are four-angled and three-angled kinds, and of each form there are species with and without horns and spines. The original Ostracion of Linnæus we may interpret as being Ostracion cubicus of the coasts of Asia, a species similar to the Ostracion rhinorhynchus. This species, cubicus, we call the type species of the genus, as the Nagg's Head specimen of Artedi was the type specimen of the species quadricornus, and the one that was used for Lister's figure the type specimen of tricornis.
Ostracion cubicus is a four-angled species, and when the trunkfishes were regarded as a family (Ostraciidæ), the three-angled ones were set off as a separate genus. For this two names were offered, both by Swainson in 1839. For trigonus, a species without horns before the eyes, he gave the name Lactophrys, and for triqueter, a species without spines anywhere, the name of Rhinesomus. Most recent American authors have placed the three-cornered species which are mostly American in one genus, which must therefore be called Lactophrys. Of this name Rhinesomus is a synonym, and our species should stand as Lactophrys tricornis. The fact that Lactophrys as a word (from Latin lætus, smooth; Greek ὀφρύς, eyebrow; or else from lactoria, a milk cow, and ὀφρύς) is either meaningless or incorrectly written makes no difference with the necessity for its use.
Fig. 241.—Spotted Trunkfish, Lactophrys bicaudalis (Linnæus). Cozumel Island, Yucatan.
Fig. 242.—Spotted Trunkfish (face view), Lactophrys bicaudalis (Linnæus).
In 1862, Bleeker undertook to divide these fishes differently. Placing all the hornless species, whether three-angled or four-angled, in Ostracion, he proposed the name Acanthostracion for the species with horns, tricornis being the type. But Acanthostracion has not been usually adopted except as the name of a section under Lactophrys. The three-angled American species are usually set apart from the four-angled species of Asia, and our cuckold is called Lactophrys tricornis. But it may be with perfect correctness called Ostracion tricorne, in the spirit called conservative. Or with the "radical" systematists we may accept the finer definition and again correctly call it Acanthostracion tricorne. But to call it quadricornis or listeri or maculatus with any generic name whatever would be to violate the law of priority.
Fig. 243.—Spineless Trunkfish, Lactophrys triqueter (Linnæus). Tortugas.
Trinomial Nomenclature.—By trinomial nomenclature we mean the use of a second subordinate specific name to designate a geographic subspecies, variety, or other intergrading race. Thus Salmo clarki virginalis indicates the variety of Clark's trout, or the cut-throat trout, found in the lakes and streams of the Great Basin of Utah, as distinguished from the genuine Salmo clarkii of the Columbia. Trinomials are not much used among fishes, as we are not yet able to give many of the local forms correct and adequate definition such as is awarded to similar variations among birds and mammals. Usually varieties in ichthyology count as species or as nothing.
Fig. 244.—Hornless Trunkfish, Lactophrys trigonus (Linnæus). Tortugas, Florida.
Fig. 245.—Hornless Trunkfish (face-view), Lactophrys trigonus (Linnæus). Charleston, S. C.
Meaning of Species.—Quoting once more from the admirable essay of Dr. Coues on the taxonomy of birds: "The student cannot be too well assured that no such things as species, in the old sense of the word, exist in nature any more than have genera or families an actual existence. Indeed they cannot be, if there is any truth in the principles discussed in our earlier paragraphs. Species are simply ulterior modifications, which once were, if they be not still, inseparably linked together; and their nominal recognition is a pure convention, like that of a genus. More practically hinges upon the way we regard them than turns upon our establishment of higher groups, simply because upon the way we decide in this case depends the scientific labeling of specimens. If we are speaking of a robin, we do not ordinarily concern ourselves with the family or order it belongs to, but we do require a technical name for constant use. That name is compounded of its genus, species, and variety. No infallible rule can be laid down for determining what shall be held to be a species, what a conspecies, subspecies, or variety. It is a matter of tact and experience, like the appreciation of the value of any other group in zoology. There is, however, a convention upon the subject, which the present workers in ornithology in this country find available; at any rate we have no better rule to go by. We treat as "specific" any form, however little different from the next, that we do not know or believe to intergrade with that next one, between which and the next one no intermediate equivocal specimens are forthcoming, and none, consequently, are supposed to exist. This is to imply that differentiation is accomplished, the links are lost and the characters actually become "specific." We treat as "varietal" of each other any forms, however different in their extreme manifestation, which we know to intergrade, having the intermediate specimens before us, or which we believe with any good reason do intergrade. If the links still exist, the differentiation is still incomplete, and the characters are not specific, but only varietal, in the literal sense of these terms."
Generalization and Specialization.—A few terms in common use may receive a moment's discussion. A type or group is said to be specialized when it has a relatively large number of peculiarities or when some one peculiarity is carried to an extreme. A sculpin is a specialized fish having many unusual phases of development, as is also a swordfish, which has a highly peculiar structure in the snout. A generalized type is one with fewer peculiarities, as the herring in comparison with the sculpin. In the process of evolution generalized types usually give place to specialized ones. Generalized types are therefore as a rule archaic types. The terms high and low are also relative, a high type being one with varied structure and functions. Low types may be primitively generalized, as the lancelet in comparison with all other fishes, or the herring in comparison with the perch, or they may be due to degradation, a loss of structures which have been elaborately specialized in their ancestry. The sea-snail (Liparis), an ally of the sculpin, with scales lost and fins deteriorated is an example of a low type which is specialized as well as degraded.
High and Low Forms.—In the earlier history of ichthyology much confusion resulted from the misconception of the terms "high" and "low." Because sharks appeared earlier than bony fishes, it was assumed that they should be lower than any of their subsequent descendants. That the brain and muscular system in sharks was more highly developed than in most bony fishes seemed also certain. Therefore it was thought that the teleost series could not have had a common origin with the series of sharks. It is now understood that evolution means chiefly adaptation. The teleost is adapted to its mode of life, and to that end it is specialized in fin and skeleton rather than in brain and nerves. All degeneration is associated with specialization. The degeneration of the blindfish is a specialization for better adaptation to life in the darkness of caves; the degeneration of the deep-sea fish meets the demands of the depths, the degeneration of the globefish means the sinking of one line of functions in the extension of some other.
Referring to his own work on the fossil fishes in the early forties, Professor Agassiz once said to the writer: "At that time I was on the verge of anticipating the views of Darwin, but it seemed to me that the facts were contrary to the theories of evolution. We had the highest fishes first." This statement leads us to consider what is meant by high and low. Undoubtedly the sharks are higher than the bony fishes in the sense of being nearer to the higher vertebrates. In brain, muscle, teeth, and reproductive structures they are also more highly developed. In all skeletal and cranial characters the sharks stand distinctly lower. But the essential fact, so far as evolution is concerned, is not that the sharks are high or low. They are, in almost all respects, distinctly generalized and primitive. The bony fishes are specialized in various ways through adaptation to the various modes of life they lead. Much of this specialization involves corresponding degeneration of organs whose functions have ceased to be important. As a broad proposition it is not true that "we had our highest fishes first," for in a complete definition of high and low, the specialized perch or bass stands higher. But whether true or not, it does not touch the question of evolution which is throughout a process of adaptation to conditions of life.
Referring to the position of Agassiz and his early friend and disciple, Hugh Miller, Dr. Traquair (1900) uses these words in an address at Bradford, England:
"It cannot but be acknowledged that the paleontology of fishes is not less emphatic in the support of descent than that of any other division of the animal kingdom. But in former days the evidence of fossil ichthyology was by some read otherwise.
"It is now a little over forty years since Hugh Miller died: he who was one of the first collectors of the fossil fishes of the Scottish old red sandstone, and who knew these in some respects better than any other man of his time, not excepting Agassiz himself. Yet his life was spent in a fierce denunciation of the doctrine of evolution, then only in its Lamarckian form, as Darwin had not yet electrified the world with his 'Origin of Species.' Many a time I wonder greatly what Hugh Miller would have thought had he lived a few years longer, so as to have been able to see the remarkable revolution which was wrought by the publication of that book.
"The main argument on which Miller rested was the 'high' state of organization of the ancient fishes of the Paleozoic formations, and this was apparently combined with a confident assumption of the completeness of the geological record. As to the first idea, we know of course that evolution means the passage from the more general to the more special, and that as the general result an onward advance has taken place; yet 'specialization' does not always or necessarily mean 'highness' of organization in the sense in which the term is usually employed. As to the idea of the perfection of the geological record, that of course is absurd.
"We do not and cannot know the oldest fishes, as they would not have had hard parts for preservation, but we may hope to come to know many more old ones, and older ones still than we do at present. My experience on the subject of fossil ichthyology is that it is not likely to become exhausted in our day.
"We are introduced at a period far back in geological history to certain groups of fishes, some of which certainly are high in organization as animals, but yet of generalized type, being fishes and yet having the potentiality of higher forms. But because their ancestors are unknown to us, that it is no evidence that they did not exist, and cannot overthrow the morphological testimony in favor of evolution with which the record actually does furnish us. We may therefore feel very sure that fishes or 'fish-like vertebrates' lived long ages before the oldest forms with which we are acquainted came into existence.
"The modern type of bony fishes, though not so 'high' in many anatomical points as that of the Selachii, Crossopterygii, Dipnoi, Acipenseroidei, and Lepidosteoidei of the Palæozoic and Mesozoic eras, is more specialized in the direction of the fish proper, and, as already indicated, specialization and 'highness' in the ordinary sense of the word are not necessarily coincident. But ideas about these things have undergone a wonderful change since those pre-Darwinian days, and though we shall never be able fully to unravel the problems concerning the descent of animals, we see many things a great deal more clearly now than we did then."
Dr. Gill observes: "Perhaps there are no words in science that have been productive of more mischief and more retarded the progress of biological taxonomy than those words pregnant with confusion, High and Low, and it were to be wished that they might be erased from scientific terminology. They deceive the person to whom they are addressed. They insensibly mislead the one who uses them. Psychological prejudices and fancies are so inextricably associated with these words that the use of them is provocative of such ideas. The words, generalized and specialized, having become almost limited to the expression of the ideas which the scientific biologist wishes to unfold by the others, can with great gain be employed in their stead." ("Families of Fishes," 1872.)
The Problem of the Highest Fishes.—As to which fishes should be ranked highest and which lowest, Dr. Gill gives ("Families of Fishes," 1872) the following useful discussion: "While among the mammals there is almost universal concurrence as to the forms entitled to the first as well as the last places, naturalists differ much as to the 'highest' of the ichthyoid vertebrates, but are all of one accord respecting the form to be designated as the 'lowest.' With that admitted lowest form as a starting-point, inquiry may be made respecting the forms which are successively most nearly related.
"No dissent has ever been expressed from the proposition that the Leptocardians (Branchiostoma) are the lowest of the vertebrates; while they have doubtless deviated much from the representatives of the immediate line of descent of the higher vertebrates, and are probably specialized considerably, in some respects, in comparison with those vertebrates from which they (in common with the higher forms) have descended, they undoubtedly have diverged far less, and furnish a better hint as to the protovertebrates than any other form.
"Equally undisputed it is that most nearly related to the Leptocardians are the Marsipobranchiates (Lampreys, etc.), and the tendency has been rather to overlook the fundamental differences between the two, and to approximate them too closely, than the reverse.
"But here unanimity ends, and much difference of opinion has prevailed with respect to the succession in the system of the several subclasses (by whatever name called) of true fishes: (1) Some (e.g., Cuvier, J. Müller, Owen, Lütken, Cope) arranging next to the lowest the Elasmobranchiates, and, as successive forms, the Ganoids and Teleosteans; (2) while others (e.g., Agassiz, Dana, Duméril, Günther) adopt the sequence Leptocardians, Marsipobranchiates, Teleosteans, Ganoids, and Elasmobranchiates. The source of this difference of opinion is evident and results partly from metaphysical or psychological considerations, and partly from those based (in the case of the Ganoids) on real similarities and affinities.
"The evidence in favor of the title of the Elasmobranchiates to the 'highest' rank is based upon (1) the superior development of the brain; (2) the development of the egg, and the ovulation; (3) the possession of a placenta; and (4) the complexity of the organs of generation.
"(1) It has not been definitely stated wherein the superior development of the brain consists, and as it is not evident to the author, the vague claim can only be met by this simple statement; it may be added, however, that the brains comparable in essentials and most similar as a whole to those of the Marsipobranchiates are those of the sharks. In answer to the statement that the sharks exhibit superior intelligence, and thus confirm the indications of cerebral structure, it may be replied that the impression is a subjective one, and the author has not been thus influenced by his own observations of their habits. Psychological manifestations, at any rate, furnish too vague criteria to be available in exact taxonomy.
"(2) If the development of the eggs, their small number, and their investment in cases are arguments in favor of the high rank of the Elasmobranchiates, they are also for the Marsipobranchiates, and thus prove too much or too little for the advocates of the views discussed. The variation in number of progeny among true fishes (e.g., Cyprinodonts, Embiotocids) also demonstrates the unreliability of those modifications per se.
"(3) The so-called placenta of some Elasmobranchiates may be analogous to that of mammals, but that it is not homologous (i.e., homogenetic) is demonstrable from the fact that all the forms intervening between them and the specialized placental mammals are devoid of a placenta, and by the variation (presence or want) among the Elasmobranchiates themselves.
"(4) The organs of generation in the Elasmobranchiates are certainly more complex than in most other fishes, but as the complexity results from specialization of parts sui generis and different from those of the higher (quadruped) vertebrates, it is not evident what bearing the argument has. If it is claimed simply on the ground of specialization, irrespective of homological agreement with admitted higher forms, then are we equally entitled to claim any specialization of parts as evidence of high rank, or at least we have not been told within what limits we should be confined. The Cetaceans, for example, are excessively specialized mammals, and, on similar grounds, would rank above the other mammals and man; the aye-aye exhibits in its dentition excessive specialization and deviation from the primitive type (as exhibited in its own milk teeth) of the Primates, and should thus also rank above man. It is true that in other respects the higher primates (even including man) may be more specialized, but the specialization is not as obvious as in the cases referred to, and it is not evident how we are to balance irrelative specializations against each other, or even how we shall subordinate such cases. We are thus compelled by the reductio ad absurdum to the confession that irrelative specialization of single organs is untrustworthy, and are fain to return to that better method of testing affinities by the equation of agreement in whole and after the elimination of special teleological modifications.
"The question then recurs, What forms are the most nearly allied to the Marsipobranchiates, and what show the closest approach in characteristic features? And in response thereto the evidence is not undecisive. Wide as is the gap between Marsipobranchiates and fishes, and comparatively limited as is the range of the latter among themselves, the Elasmobranchiates are very appreciably more like, and share more characters in common with them, than any other; so much is this the case that some eminent naturalists (e.g., Pallas, Geoffroy, St. Hilaire, Latreille, Agassiz, formerly Lütken) have combined the two forms in a peculiar group, contradistinguished from the other fishes. The most earnest and extended argument in English, in favor of this combination has been published by Professor Agassiz in his 'Lake Superior,' but that eminent naturalist subsequently arrived at the opposite conclusions already indicated.
"The evidences of the closer affinity of the Elasmobranchiates (than of any other fishes) with the Marsipobranchiates are furnished by (1) the cartilaginous condition of the skeleton; (2) the post-cephalic position of the branchiæ; (3) the development of the branchiæ and their restriction to special chambers; (4) the larger number of the branchiæ; (5) the imperfect development of the skull; (6) the mode of attachment of the teeth; (7) the slight degree of specialization of the rays of the fins; and (8) the rudimentary condition of the shoulder-girdle."