CHAPTER XIV MARINE VERTEBRATES

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The vertebrates form the highest sub-kingdom of animal life—the sub-kingdom to which we ourselves belong, the chief distinguishing characteristic of the group being the presence of an internal skeleton, the principal part of which consists of a rod or column of cartilaginous or bony material running along the dorsal side of the body, known as the vertebral column.

Fig. 225.—Transverse section through the Bony Framework of a Typical Vertebrate Animal

1. Spinous process of the vertebra. 2. Neural arch. 3. Transverse process. 5. Body of the vertebra. 6. Breast-bone. 7. Rib. The space between 2 and 5 is the neural cavity; and that between 5 and 6 is the visceral cavity

This column is usually composed of a number of elements called vertebrÆ, each of which gives off two processes that unite and form an arch on its dorsal side, while all the arches form a tube through which passes the central portion of the nervous system.

Below, or on the ventral side of the column, is the body-cavity containing the organs of digestion and circulation; so that if we make a transverse section of a vertebrate animal we find that there are two distinct tubes or cavities—a neural or cerebro-spinal cavity on the dorsal side of the vertebral column, formed by extensions from the substance of the latter, and enclosing the chief portion of the nervous system; and a body-cavity on the ventral side containing the viscera or internal organs.

The above features are highly important, and will always prove quite sufficient to enable us to decide whether any particular animal is a vertebrate or an invertebrate, for it will be remembered that the body of the latter has only one cavity, containing the nervous system as well as the viscera, and that the nervous system is commonly placed along the ventral side, but never along the dorsal. In addition to this the vertebrates never have more than two pairs of limbs, and these are always directed from the nervous system; and the jaws, which are appendages that move in the horizontal plane in invertebrates, are, in the higher animals, portions of the framework of the head and move vertically. In vertebrates, too, there is always a complete blood system, consisting of a heart with two, three, or four cavities, a system of arteries to convey the blood to the different parts of the body, veins to return the blood to the heart, and networks of fine capillaries connecting the former with the latter.

All vertebrates, at an early stage of their existence, have a cartilaginous rod running through the dorsal portion of the body, called the notocord. In some of the lowest animals of the division this rod persists without any important alterations in structure, while in the higher forms it gives place to the series of cartilaginous or bony elements above referred to as the vertebrÆ; and the arrangement of the vertebrates into their relative positions in the scale of life is based largely on the degree of development of the vertebral column from the notocord. Another interesting feature in the development of a vertebrate is the formation of five or more transverse, archlike thickenings on each side of the digestive tube, just behind the head; and, in the spaces between them, of a series of slits forming a communication between the pharynx and the exterior. These arches and clefts have but a brief existence in many vertebrates, while in others they persist throughout life; and, like other points referred to, they assist us in recognising the relations of the vertebrates to one another.

The vertebrates are divided into the following classes:—

1. Cyclostomata—Lampreys.
2. Pisces—Fishes.
3. Amphibia—Frogs, Toads, Newts, &c.
4. Reptilia—Snakes, Lizards, Tortoises, &c.
5. Aves—Birds.
6. Mammalia—Mammals.

The first of these includes only a few species, one of which is found in our seas, and will receive a short notice here. The fishes will, of course, demand a fair share of our attention. Amphibians and reptiles have no British marine representatives, and are therefore quite excluded from this work. As to the birds, although there are so many that live entirely on the sea and in its immediate neighbourhood, these have been so ably dealt with by Mr. Hudson in one of the books of this series that it would be superfluous to mention them. The mammals include a considerable number of marine species, but as only one of these—the Porpoise—is really commonly observed round our coasts, it alone will be selected for description.

Lampreys and their few allies were formerly classified with fishes, but are now made to form a small class by themselves; and there is abundant reason for the separation. It will be remembered that vertebrates, in the early stages of their development, are characterised by a cartilaginous rod running through the dorsal region of the body, below the central cord of the nervous system, and that they possess a series of slits opening into the sides of the pharynx. Now, while these characteristics are usually only transitory in the vertebrates, the Lampreys and their relatives are the only animals in which they persist throughout life, and it is for this reason that they are exalted to the dignity of a class under the title Cyclostomata.

This name signifies ‘round-mouthed,’ while the Lampreys themselves form the still smaller division Marsipobranchii, which means ‘pouch-gilled,’ these two being among the most evident characters of the creatures concerned. They have no true jaws, the circular mouth being supported by a ring of cartilage, and provided with a rasp-like tongue that enables them to divide their food. They have no true bone in their bodies, the simple skeleton, without limbs and ribs, being entirely cartilaginous, and the rudimentary skull is not movable on the dorsal cartilage. Their bodies are elongated and eel-like, with a single medial fin, supported by fine cartilaginous rays, and with seven little slits on each side of the neck, communicating with as many gills in the form of little pouches. The mouth is suctorial, presenting, when open, a circular adhesive disc, by which the animals can attach themselves to any solid object, but assumes the form of a mere slit when closed. The young differ from the adult in a few points of structure. Thus they have no eyes, and the long fin, divided in the adult, is continuous. With the above characteristics in mind, there will be no danger of confusing the lampreys with the eels and other similar fishes.There are three or four British lampreys, two or three of which inhabit fresh water. Their habits do not seem to be well understood, but it appears certain that the Sea Lamprey (Petromyzum marinus), which reaches a length of from one to two feet, ascends rivers to spawn, while the smaller River Lamprey (P. fluviatilis) has been caught in the sea; and it is probable that the migrations of both, together with the sojourn of the young of the former for a longer or shorter period in fresh waters, have been the cause of the widespread confusion between species.

Lampreys are carnivorous creatures, and attach themselves to fishes by their suctorial mouths, and rasp away the flesh. They have also been known to attack bathers.

Fig. 226.—The Sea Lamprey

Passing now to the true fishes, we must first study the general features of the group by which they are to be distinguished from other animals. Since there are so many creatures outside this class that are more or less fishlike in some respects, it becomes no easy matter to give a concise definition of a fish, and the shortest satisfactory description must necessarily include several points of structure. Thus, we may define a fish as a cold-blooded vertebrate that does not undergo metamorphoses, with limbs modified into fins, possessing also median fins on the dorsal and ventral surfaces, having distinct jaws, a heart with two chambers, and breathing by gills. To this we may add that the young are generally produced from eggs, and that the skin is covered with scales or bony plates, or is naked.

But let us now look more closely into the structure of fishes, so that we may be enabled to see how marvellously they are adapted to their aquatic life, and in order that we may become acquainted with the few technical terms which will, as a matter of convenience, be used in the descriptions of species.

Taking first the external features, we note that the body is generally covered with scales, sometimes very large and distinct, but often so small and closely set that they are not visible without careful examination; indeed they are often so small, and so thoroughly embedded in the slimy skin as not to be discovered without the aid of a microscope. When the scales have unbroken edges and overlap one another they are said to be cycloid, but when the projecting edges are toothed or serrated, giving a roughness to the touch, they are described as ctenoid. Sometimes the scales are modified into bony plates or little isolated bony granules, and in either case they are practically identical in structure with teeth, consisting as they do of dentine, capped with a little harder substance resembling enamel.

Fig. 227.—The Pilchard

1. Dorsal fin. 2. Pectoral fin. 3. Pelvic fin. 4. Ventral or anal fin. 5. Caudal fin.

We often observe a row of scales, of a different nature from those covering the body generally, running along each side of a fish from near the eye to the end of the tail; and these constitute what is called the lateral line. If we examine these scales closely, we observe that each one is pierced by a hole that communicates with a little sac beneath containing a gelatinous material, and in which a nerve tendril terminates. The presence of the nerve filament evidently denotes that the scales in question, with the little sacs beneath them, are organs connected with sensation, and it is also believed that they have something to do with the secretion of the slimy mucus that covers the scales of the body.

The mouth of a fish is generally situated on the extreme front of the head, but occasionally, as in the sharks and rays, quite on the under side. If it contains a tongue at all, this organ is of small size and simple structure; thus it is highly probable that the sense of taste is very feeble in these animals, and this is just what one might expect when one remembers that fishes never retain their food in the mouth for any length of time, but simply bolt it without any attempt at mastication.

The arrangement and nature of the teeth are very variable. Often they are developed on the membrane of the mouth only, in which case they are generally renewed as fast as they are worn down, but sometimes they are persistent structures more or less embedded in the bone of the jaws. In some cases teeth are altogether wanting, but in others they are situated not only on the jaws, but also on the tongue, the roof of the mouth, and even on the bony arches that support the gills.

A glance at the fins of a typical fish will suffice to show that they may be divided into two groups—the paired fins, representing the two pairs of limbs in most of the higher animals, and the median fins occupying the middle line of the body. The former comprise the two pectoral fins that correspond with our arms, and are attached to the bones of the pectoral or shoulder girdle; and the pelvic fins, corresponding with the lower extremities. The pectorals, too, are present in nearly all fishes, while the pelvic pair are rather more frequently absent than the pectorals.

The medial fins comprise the dorsal, the ventral, and the caudal or tail-fin, and are not to be regarded as limbs, but rather mere outgrowths of the skin. They are not directly connected with any part of the main bony framework of the body, though they are generally jointed with a series of bones (interspinal bones) that run between processes of the vertebral column. The dorsal and ventral fins are often divided into two or more parts, and the tail fin is commonly distinctly forked.

Although the seven fins above mentioned differ considerably in general form, some being fanlike, while others form fringe-like expansions, yet they generally agree in that they consist of bony or cartilaginous rays, between which is a soft membrane. The rays, however, vary much in character, being sometimes developed into very hard and sharp spines, and sometimes quite soft and flexible. The fins also differ in function, as will be seen when we observe the movements of a fish as it swims. It will then be noticed that the caudal fin, which is spread in the vertical plane and moved sharply from side to side by the powerful muscles of the tail, is the chief propelling organ, while the others are concerned principally in maintaining the balance of the body. This latter point becomes much more evident when we observe the movements of a fish in which one or more of the fins have been injured or lost, as we shall see presently.

It is true that the pectoral fins are sometimes used to propel, but forward movement is brought about almost entirely by the caudal fin, which acts much in the same way as the blade of the propelling ‘screw’ of a steam-vessel, the pectorals being used at the same time for steering. Occasionally, too, the latter are both spread out at right angles to the body when the fish desires to stop suddenly, and are even employed at times in swimming backwards.

When a fish wants to turn to one side, it will be seen to give the tail a sharp motion to the opposite side. The pectoral of the latter side is also brought into play, while the other is kept close against the body.

If the pectoral or pelvic fin of one side is injured, the body of the fish will incline to the opposite side; and if all the paired fins are functionless the fish swims with its head inclined downwards. Observations of fishes in which the dorsal or ventral fins are injured will also show that these organs are necessary to maintain a steady motion in the water.

In addition to the above facts, it may be mentioned here that the paired fins are often modified into long finger-like processes that serve as organs of touch, and even as means by which the fish can creep along the bottom. This is notably the case with gurnards and a few of the other fishes that spend their time almost exclusively on the bed of the sea.

Fishes are essentially gill-breathers, the gills being generally fringe-like organs, supported on bony arches (the gill arches), numbering four on each side, the cavity containing them being covered by a gill-cover (operculum) that opens behind. Water is taken in at the mouth, whence it passes into the gill-chamber; and after passing between and around the gills, it escapes under the opercula. The gills themselves are richly supplied with bloodvessels that are distributed close to the surface, and an exchange of gases takes place through their exceedingly thin walls, carbonic acid gas passing from the blood to the surrounding water, and oxygen, held in solution in the water, passing from the water to the blood.

When fishes are in foul water, containing but little oxygen in solution, they rise to the surface in order to make up the deficiency by taking oxygen direct from the air. This, however, is an unnatural proceeding with the majority of fishes; but there are some that are provided with accessory breathing organs specially adapted to the extraction of oxygen direct from the air, and these are so dependent on the supply from this source that they are suffocated if prevented from reaching the surface.

In other fishes, such as the sharks and rays, the gills are of an entirely different character from those described above, for they are pouch-like and five in number on each side, each pouch communicating with the pharynx as well as with the exterior by a slit-like opening.

Before leaving the external characters of fishes we must say a word or two about their forms and colours. As regards the former, it is well known that fishes are well adapted for rapid progression through water, but there are many exceptions to this rule. These exceptions, however, apply principally to those species that have no need to swim rapidly, and a study of their habits will show that their form is just as perfectly adapted to their mode of life. They are often species that live on the bottom, or hide in the crevices and holes of rocks, and examples will be given in our future descriptions.

Variations in colour are even more interesting, especially as they are so commonly connected with the nature of the surroundings and the protection of the animals. In nearly all cases the colour is darker on the upper surface than on the lower, thus making it appear that the influence of light has something to do with the formation of the pigments of the skin, and experiment proves that this is, at least to a certain extent, the case; for when fishes have been kept for some time in an aquarium into which light is admitted through the bottom only, pigment spots have formed in the skin on the lower surface.

Fishes that swim at the surface are generally tinted on the dorsal side with some shade that closely resembles the colour of the water as viewed from above, and are white and silvery below. Such colouring is of course highly protective, for they are not readily distinguished by the sea birds and other enemies that would pounce on them from above, and are almost invisible against the sky to eyes below. This form of protective resemblance is beautifully illustrated in the mackerel, which is barred on the back with black and green, closely imitating the ripples on the surface of the deep green sea, while the under side is of a silvery whiteness that is hardly visible from below with the bright sky as a background.

The flat fish afford other interesting examples, for these live on the bottom, and are coloured above so as to resemble the bed on which they live; the tints being those of mud, sand, or gravel.

But what are we to say of the gaudy colours of the gurnards, rock fishes, &c.? These are certainly not protective in all cases, for we sometimes find brightly coloured species conspicuous among duller surroundings. Such instances, however, are comparatively rare, the gaudy species living principally among the variously coloured rocks, weeds, and corals; and when they do occur it is probable that they serve principally as a means by which the brightly coloured sex—usually the male—attracts its mate. We say ‘usually the male,’ but why so? Because the female requires the protection of a more sombre colour in order that she may with safety deposit her spawn for the perpetuation of her species. Again, the male referred to needs the assistance of his gaudy coat only during the breeding season, hence we find that he assumes the bright colours as a wedding garment, to be cast off when the breeding season is over.

This leads us to the subject of changeability of colours in the same individual. That such changes do occur is well known, and it is still more remarkable that they are produced in rapid succession, apparently at the will of the fish concerned; for its tints will vary as it moves from place to place so as to always harmonise with the surroundings, and also in response to other conditions. The mechanism by which such variations are produced has also been studied and explained:—The colouring matter is held in little vesicles beneath the skin, and these vesicles are capable of being compressed by muscles quite under the control of the fish. When they are globular in form the contained pigment appears dark, but when they are flattened by muscular compression, the pigment is spread over a much larger area, and thus greatly reduced in depth of tint.

As with all vertebrates, the central axis of the internal skeleton of a fish consists of the backbone and the skull. The structure of the latter is so complicated, and its description so full of technicalities, that we deem it advisable to pass it over in a work like this where the scope is so large in proportion to the space available; and this we do with reluctance, because the detailed study of the skull is of real importance to those who would thoroughly understand the principles of classification.

The backbone consists of a variable number of cylindrical vertebrÆ, united end to end to form a continuous column, both the anterior and posterior faces of each being concave. On the dorsal surface of each vertebra there is a V-shaped arch, surmounted by a spine, the former serving to protect the spinal cord, and the latter giving attachment to the muscles of the back. Some of the vertebrÆ are also provided with processes for the attachment of the ribs, and those of the tail possess an arch and a spine on the ventral as well as on the dorsal side.

It has already been shown that the pectoral fins are jointed to a girdle. This girdle corresponds with the shoulder-blade of higher animals, and gives direct attachment to the rays of the fin, which may be regarded as the equivalent of the fingers, and thus there is no part of the limb corresponding with the arm. The pelvic fins also are frequently jointed to a pelvic girdle or hip, but this is a very rudimental structure, or is even entirely absent in some species.

The rays of the caudal fin articulate with the extremity of the backbone, but this portion of the fish’s anatomy undergoes such remarkable changes that we must devote a few words to it. It is probably well known to our readers that the tails of fishes exhibit three distinct forms. The first of these is a simple fringe formed by the union of unaltered dorsal and ventral fins; the second is the unsymmetrical or unequally lobed tail so characteristic of sharks, dogfishes, and rays; and the third is the broad symmetrical tail fin, often distinctly forked or bi-lobed, such as we meet with in the majority of our bony fishes. These three kinds are known respectively as the diphycercal, heterocercal, and the homocercal tails.

Fig. 228.—The Skeleton of a Fish (Perch)

d, dorsal fin; p, pectoral fin; v, pelvic fin; t, tail fin; a, anal fin

Now, it is an interesting fact that the most ancient fishes of our globe possessed tails of the first type; and that these gradually gave place to the heterocercal form; while the higher fishes of the present day nearly all possess the homocercal tail. Thus as time advanced the heterocercal tail was gradually evolved from the diphycercal, and the homocercal from the heterocercal.Further, if we watch the development of one of the highest fishes of the present day from its embryo, we find that similar changes take place in the individual. At first its tail is a simple fringe round the extremity of the backbone, the latter being straight, or nearly so, to the end, so that the embryo fish, as yet still in the egg, reflects a characteristic of its very early ancestors. Then the end of the vertebral column turns upward, and strong fin-rays are developed on its ventral side, so that the tail becomes a heterocercal one like that of the less remote ancestors of a later geological period. Next, the upward-bending portion of the vertebral column is slowly absorbed, till nothing of it remains except a small upturned bony spine, while, at the same time, the ventral lobe expands on the upper side until the tail fin is once more of a symmetrical form.

Fig. 229.—The Internal Organs of the Herring

a, oesophagus; bc, stomach; e, intestine; l, duct of swimming bladder; k, air-bladder; h, ovary

Following these interesting changes, it becomes evident that the symmetry of the tail fin of the bony fishes is really a false one, the whole of it having been formed from the ventral lobe of a heterocercal tail; and although the backbone seems to terminate abruptly exactly opposite the middle of the fin, it still contains the remnant of the raised extremity of the backbone that ran to the tip of the dorsal lobe when the tail was of the heterocercal type.

The flesh or muscle of fishes is usually white, but it often assumes a pink colour in the case of those fishes that feed largely on crustaceans. This is due to the presence of a substance in the horny or calcareous skins of the crustaceans that is turned red by the action of the digestive fluids—the same substance that is turned red when the crustaceans are boiled. This is notably the case with the salmon; but the red pigment thus derived originally from the crustaceans frequently shows itself more in the skin of the fish than in the flesh, as observed in the common red gurnard.

Most fishes possess a membranous bag containing air, situated just below the backbone, and known as the air-bladder; but this organ does not exist in sharks and rays and in some of the heavier bony fishes that live on the bottom. The air-bladder is capable of being compressed by the action of certain muscles, and its principal use seems to be the adjustment of the specific gravity of the fish to that of the surrounding water; but it is interesting to note that the development of this air-bladder is precisely the same as that of the lungs of air-breathing animals, and that in some fishes which live in foul muddy waters it is really a functional lung by means of which the fishes can breathe direct from the atmosphere.

We can find space to refer only to one other internal structure of the fish, namely, the roe of the female. This usually consists of a very large number of eggs of small size, sometimes numbering many thousands, and even millions, in a single individual. So numerous, indeed, are the eggs, that were it not for the multitudes of carnivorous animals that devour both eggs and fry, the sea and fresh-water lakes and rivers would soon become so thickly populated that the fish would die in millions for lack of food and air.

In some cases, however, the eggs are much larger and fewer in number, but these are generally protected from the ravages of predaceous species by a hard covering, as we shall observe in the sharks and rays.

Finally, a word or two must be said about the distribution of fishes. We have already referred briefly to species that live principally at the surface, and others that make the bottom their home: but some of the former go to the bottom for food or to deposit their spawn, while some of the latter occasionally rise to the surface and swim in shoals. We have noticed, too, that the paired fins of bottom fishes are sometimes modified into feelers, or into fingerlike processes adapted for creeping. Similar organs, employed undoubtedly as organs of touch, and called barbels or barbules, are often developed on the chins or jaws of these fishes.

Although we have to deal principally with the species that belong more or less to the shore—the littoral fishes—we should like to refer briefly to one or two interesting features of those that live at great depths. It will be readily understood that much light is lost as the rays penetrate into deep water, so that the bottoms of deep seas must be more or less darkened. To allow for this loss, we find that the species living at moderate depths are provided with larger eyes to enable them to see their prey and their mates; but at still greater depths, where the sun’s light cannot penetrate, the fishes are either blind, or are possessed of luminous organs which enable them to see their way. Again, as the sea is so thinly populated at such great depths, the carnivorous species do not find abundant food always at hand, hence they are often provided with such mouths and stomachs as will allow them to make the best of favourable opportunities, some being capable of swallowing a fish quite as large as themselves.

We often find fishes roughly classified into fresh-water and salt-water species, and although such a division is at times convenient, it must be remembered that some of the former migrate into brackish and even into salt water, while some of the latter ascend estuaries and rivers either for the purpose of obtaining suitable food, or for the deposition of their eggs.

The fishes that frequent our coasts may be classified into two main groups, those with cartilaginous skeletons (Elasmobranchii), and the bony fishes (Teleostomi). Both these are divided into family groups, and we shall deal more or less briefly with all the important families that include common British marine fishes, but giving more attention to those species that are truly littoral in habit—species that may be found in the rock pools or under stones at low tide, and which may be obtained by the amateur angler working from rocks, piers, &c.

The cartilaginous fishes include the Sharks, Dogfishes, and Rays. They have pouchlike gills, five or more on each side, each one opening to the exterior by a separate slit. The skin generally contains bony elements that are toothlike in structure and often in form; the mouth is usually on the under side of the head, and the tail is nearly always of the heterocercal kind. They are all carnivorous creatures, and often exceedingly voracious; and are represented in our seas by the Rays and Dogfishes.

Rays or Skates (family RaiidÆ), of which there are six or seven British species, are readily known by their broad flattened rhomboidal bodies, with the mouth on the under side of the head, a longitudinal fold on each side of the tail, and pectoral fins extending quite or nearly to the front point of the head.

Two of these fishes are very common in our markets, one being the Thornback Skate (Raia clavata), distinguished by the clawlike spines down the middle of the back as well as on other parts of the body; and the Common Skate (R. vulgaris), a very voracious species, from two to four feet long, with a very sharp muzzle.

All the members of this family are bottom fish, without air-bladders; and their eggs, which are large and detached, are enclosed in horn capsules which are so commonly washed up on the beach that they are well known to frequenters of the sea-side, who call them Skates’ Barrows or Shepherds’ Purses. These cases are oblong in form, with a process at each corner, and the material of which they are composed looks very much like that of some of the coarser sea weeds after they have been dried in the sun. As a rule only the empty cases are cast ashore by the waves, open at the end where the little skate made its escape; but occasionally we meet with the complete egg, and the case, while still wet, is sometimes sufficiently transparent to show the form of the embryo within.

Fig. 230.—The Egg-case of Dogfish

Dogfishes are also fairly well known to sea-side ramblers, for not only are some species used as food in many places, but they are also frequently to be seen cast aside with the refuse from the fishermen’s nets. The common Spiny Dogfish (Acanthias vulgaris), belonging to the family SpinacidÆ, frequents all parts of our coasts. It reaches a length of three or four feet, and is of a slate-blue colour above and very pale yellow below. The pectoral fins are very large, the ventral fin absent, and there is a very sharp spine in front of each dorsal. The creature is ovo-viviparous; that is, the eggs are hatched while still within the body of the parent.

Another family (ScylliidÆ) contains two British species without spines, and is also characterised by having the first dorsal fin far behind. They are the Larger Spotted Dogfish (Scyllium canicula) also known as the Nurse Dog and the Bull Huss; and the Lesser Spotted Dogfish (S. catulus), called also the Huss and the Rough Hound. The egg capsules of both these are occasionally washed on the beach, and those of the latter species may be known by the yellowish colour and the long tendrils by which they are anchored to sea weeds.

In addition to these we may briefly refer to two of the Blue Sharks (family CarchariidÆ) that frequent our shores, distinguished by their long and prominent muzzle, and the crescent-shaped mouth. They may be regarded as higher in the scale of fish life, as compared with the sharks and rays previously named, because the vertebrÆ are more or less hardened by the deposit of calcareous matter, and, therefore, make a nearer approach to the character of true bone. The species referred to are the Common Blue Shark (Carcharius glaucus), and the Smooth Hound (Mustelus lÆvis). The former often exceeds twelve feet in length, and is commonly seen off our south and west coasts during the summer months. It is a nocturnal marauder, and is said to sleep at the surface by day with its tail exposed above the water. The Smooth Hound is a bottom feeder, subsisting on molluscs and crustaceans, the shells of which are easily crushed by its flat and blunt teeth. It is a small shark, measuring only three or four feet in length, and brings forth its young alive.

Fig. 231.—The Smooth Hound

The next division (Teleostomi) contains all the bony fishes, which may be distinguished generally from the cartilaginous group by the following features:—The skeleton is more or less hardened by the deposit of calcareous matter, and the tail is generally not of the heterocercal type. The paired fins are fan-like, and the pectoral girdle is attached to the hinder part of the skull. These fishes generally have an air-bladder, and the gills lie close together in a cavity covered by an operculum. The eggs, too, are generally very small and numerous, and massed together.Of these we will take first the family SalmonidÆ, of which the Salmon (Salmo salar), and the Smelt (Osmerus eperlanus) are well-known examples. Several species of the family are remarkable for their periodical migrations from fresh to salt water or vice versa, and we cannot do better than briefly relate the interesting life-history of the salmon as a striking instance of these peculiar wanderings. This fish quits the sea at the close of the summer, and ascends the rivers for the purpose of depositing its spawn, the colder water of the rivers being necessary for the development of the young. Its upward journey is beset with many difficulties, for it has to shoot the various rapids and leap the cascades, the latter often demanding the most prodigious efforts on the part of the fish, which frequently leaps several feet out of the water, and even then has sometimes to renew its attempts over and over again before it finally succeeds. Indeed, the difficulties to be overcome are so numerous that the fish often reaches the goal in such an exhausted condition that it would hardly be recognised as the salmon by those who have only seen it in the prime condition in which it is captured during its return to the sea in the following spring or summer. The male, at this period called the kipper, is of a dull red colour, irregularly blotched with yellow and light brown, and its skin is covered with a slimy secretion. Its body is lean, and the head, now large and out of all proportion, is rendered still more unsightly by the protrusion of the lower jaw, which at this season, when the males are particularly pugnacious, becomes a formidable weapon of offence. The condition of the female, now called the baggit, is equally poor, and the skin has changed its bright silvery colour for dark and dingy shades.

The female digs a nest in the form of a deep trench by wriggling her body in the gravel of the bed of the stream, and there deposits her eggs, many thousands in number, small quantities at a time. As each batch is deposited the eggs are fecundated by the kipper, and then covered over lightly with gravel by the baggit; and this work having been accomplished, both male and female rest and feed, with the result that their condition is rapidly improved.

After about eighteen weeks the eggs begin to hatch, and the fry wriggle out of the nest and seek shelter under stones in the immediate neighbourhood. They are now peculiar little creatures, as much like tadpoles as fishes, with big heads and narrow bodies, and a bag of albuminous yolk-matter attached to the ventral side. The young subsist on this store of food for from twelve to twenty days, during the whole of which time they remain under shelter, having, of course, no need to expose themselves to the numerous enemies with which they are surrounded, and they then leave their hiding-place in search of food, being now about an inch in length. They feed on aquatic and other insects, which are now becoming plentiful on the approach of the warm weather; and, growing rapidly, reach a length of four inches in a month or two. They are now called parr, and are distinguished by the dark bars that cross their bodies transversely—a feature that persists for a year or more from this time.

Towards the end of May the parr migrate seawards, accompanied by the adult salmon, but as their enemies include the voracious fishes, wading birds, and even the adults of their own species, it is probable that only a small proportion of the original number ever enter salt water.

In the sea they feed on crustaceans, molluscs, and small fishes, the young still growing rapidly, and attaining a weight of about five pounds in the following autumn, when both young (now called grilse) and old again ascend the rivers to spend the colder half of the year; the former will have reached a weight of ten pounds or more on their return to the sea in the following year.

The Smelt may be seen in thousands in our estuaries during the spring, for at that time they come up to spawn in the brackish water. In the summer they swim about in shoals along the coast, and are caught largely in nets for the market. In some parts they are taken in large shallow circular nets suspended on a line. This is lowered into the water, and hauled up when the fish are seen swimming above it. Many amateurs secure numbers of smelt by means of rod and line, fishing from piers, jetties, &c. They bite freely at almost any kind of bait, and will snap at an almost bare hook, with the tiniest fragment of the bait at its point.

The Herring family (ClupeidÆ) contains some well-known food-fishes to which we need only casually refer. They are mostly littoral species, none inhabiting deep water, and none straying into the open ocean. Their bodies are covered with silvery scales, and are laterally compressed, so much so on the ventral side that there is a moderately sharp ridge along the middle line. The principal fishes of the family are the Herring (Clupea harengus), the Sprat (C. sprattus), and the Pilchard (C. pilchardus).These fishes are particularly interesting on account of their gregarious habits and the enormous size of the shoals they form, a single shoal often containing millions of individuals; and they are often captured in such quantities that large numbers are sold to farmers as manure to enrich the soil. The shoals are followed closely by many larger carnivorous species that devour them in great numbers, as well as by flocks of sea birds that prey on them, and yet their numbers are not appreciably reduced by such ravages. They spawn in shallow waters near the coast, and feed principally on the crustaceans and worms of the littoral zone.

Sprats were once considered to be the young of the Herring, but it is now universally acknowledged that they are a distinct species, and quite a number of characteristics have been given as a means of distinguishing between the two. The young of the herring are, however, used largely as food, for that miscellaneous mixture of fry and small species known as Whitebait consists largely of these and the young of the sprat.

Fig. 232.—The Common Eel

Herrings are captured principally off the north and east coasts, but the pilchards, which are often confused with them, and even at times sold under the same name, are caught chiefly off the coast of Cornwall.

Although the Eels (AnguillidÆ) are so readily distinguished by their general form and appearance, yet it may be advisable to call attention to one or two of the leading characters that would possibly be overlooked by an ordinary observer, and in doing this we ask the reader to note that our remarks apply to the true eels only, and not to the sand eels and other fish that may be confused with them.

The elongated bodies of the AnguillidÆ are covered with a slimy skin that is apparently scaleless, but an examination with the microscope will show that there are small scales embedded in it. The dorsal and ventral fins extend to the tail, and the pelvics are absent; the gill-slits, which are very narrow, are at the base of the pectorals.

It might well be expected that eels would be possessed of some form of accessory breathing apparatus, seeing that they can live so long out of water, but this is not the case. They have, however, a pouch-like gill-cavity which can be inflated and filled with water by the fish, thus keeping the gills moist and functional. In most other fishes the gill-chamber is not capable of holding water, and thus the gills soon become dry and sticky, so that they adhere together and fail to absorb the necessary oxygen when the fish is out of water.

Thus the Eel (Anguilla vulgaris), in the remarkable migrations for which it is noted, is capable of travelling over dry land for considerable distances in search of suitable homes.

If an eel be taken out of the water, these gill-pouches will be seen to swell out almost immediately, and remain filled with water as long as the fish is kept on land; but when it is returned to its natural element, it will at once discharge the water that kept its gills moist, and which has become foul with the products of respiration, and, with a few vigorous gulps, renew the supply.

Eels spend their breeding season, which extends from July to September, in salt or brackish waters; and early in the following summer, the young, which are now called elvers, and measure from three to five inches in length, ascend the rivers, travelling enormous distances and overcoming obstacles that we might well expect to be insurmountable. Thus they perform two migrations annually, though it is thought by some observers that the adult never returns to the sea, but dies soon after it has deposited its spawn.

The family of Flat-fishes (PleuronectidÆ) present many interesting points of structure and habit in which they stand alone, the variations in structure as compared with other fishes being due, of course, to the habits which they have acquired.

One of the first features that strike the observer on looking at a flat-fish is the unsymmetrical form of the body. It is very much compressed, and the fish having acquired the habit of lying on the bed of the sea, sometimes on the left and sometimes on the right side, the lower surface has become flattened more, and is of an almost pure white colour, while the upper convex side is more or less coloured with pigment produced by exposure to light. The dorsal and ventral fins are both very long; and, as is usual with bottom fishes, the swimming or air bladder is absent.

Young flat-fish are at first perfectly symmetrical in form, with one eye on each side of the head, and they swim freely in the water with their bodies in a vertical plane; but they very soon acquire the habit of swimming on one side, and the eye of that side slowly passes round to the other side of the skull, rotating in its orbit as it moves, till at last both are on the uppermost surface. This, of course, is accompanied by a considerable distortion of the bones of the skull, which is very evident in the skeleton of the adult. The young fish then takes to the bottom, with the result that its under-surface is flattened, while the upper becomes strongly pigmented.

These fish spend almost the whole of their time on the bottom, only occasionally rising for short intervals, when they swim by undulatory movements of their bodies and fins; their food consists of crustaceans, worms, and other small marine animals.

They furnish very interesting illustrations of protective colouring, the upper surface always closely resembling the ground on which they rest and feed; and thus they are not only protected from their own enemies, but are enabled to lie unseen by the animals that form their prey. Those which live on sandy shores are finely spotted with colours that closely imitate the sand, while those that lie on mud are of dark and dingy hues. Others, again, are irregularly marked with spots of various sizes and colours that resemble a gravelly bottom; and most species are still further protected by their habit of throwing sand or mud on the top of their bodies by means of their dorsal and ventral fins.

Small flat-fishes, especially young Plaice and Flounders, live so close to the shore that they are often left behind in rock pools and sandy hollows by the receding tide, and it is very interesting to observe the habits of these in their natural conditions. It will generally be noticed that it is most difficult to detect them while they are at rest; and when disturbed, they usually swim but a short distance, settling down very abruptly, and immediately throwing a little sand over their bodies by a few vibrations of their fins.

Another peculiarity of some of the flat-fishes is their indifference to the nature of the water in which they live. Flounders may not only be caught in the estuaries of our rivers, but they even ascend to, and apparently live perpetually in, perfectly fresh water. In many instances they may be seen miles from the sea, and even flourishing in little fresh-water streams only a few feet in width. Thus they may be found in numbers in the upper waters of the small rivers of the Isle of Wight and of many streams of the mainland.

The principal British flat-fishes are the Plaice (Pleuronectes platessa) and Flounder (P. flexus) above mentioned, and also the Sole (Solea vulgaris), the Lemon Sole (S. aurantiaca), the Turbot (Rhombus maximus), and the Halibut (Hippoglossus vulgaris); and as all these are well-known food-fishes it is hardly necessary to describe them.

Fig. 233.—The Lesser Sand Eel

Sand Eels (family OphidiidÆ) resemble the true eels in the general form of their elongated bodies, but may be readily distinguished by their bright silvery colour, the large gill-openings, and the more strongly developed dorsal and ventral fins, the former of which extends almost along the whole length of the back. The lower jaw is also longer than the upper.

Two species are to be found on our shores—the Lesser Sand Eel (Ammodytes tobianus), and the Greater Sand Eel (A. lanceolatus), the former attaining a length of six or seven inches, and the latter nearly three times this size. They may be seen off the south coast, swimming in shoals over sandy bottoms, and when disturbed they descend and burrow into the sand with remarkable agility. They approach the shore so closely that they are often washed up by the waves, but immediately disappear into the sand; and large numbers commonly remain behind as the tide recedes, burying themselves to the depth of a few inches, and are dug out by fishermen for bait.

The smaller species is by far the more common, and is taken in large numbers by means of the draw net to be sold as food. It is particularly abundant at Teignmouth, where it is known as the Sand Sprat, and forms an important article of diet.

Quite a number of our important food-fishes belong to the Cod family (GadiadÆ), and although some of these are caught almost entirely in deep water some distance from shore, others give employment to the angler fishing from rocks, piers, and jetties.

In all, the gill-openings are very wide, and the body is covered with small overlapping scales. The caudal fin is quite free, the dorsal is generally divided into three distinct parts which extend over the greater part of the back, and the ventral fin is also frequently divided.

Fig. 234.—The Three-bearded Rockling

The typical species—the Cod (Gadus morrhua)—is too well known to need a description, and although it is a large fish, often measuring four feet and more, it approaches so close to the shore that it may be caught with a hand line thrown out from rocks or piers. The barbel projecting from the chin denotes that it is a bottom feeder.

On the rocky coast of the south the Pollack or Pollock (G. pollachius) is very abundant, and may be taken with rod and line from the shore. It also enters estuaries in large numbers, and may be caught close to quays and jetties. This species is a very free biter, and will take almost any of the baits used for sea fishing. It has no barbel.

The same genus includes the Whiting (G. merlangus), distinguished by a black spot at the base of the pectoral fin and the absence of barbels; the Whiting Pout (G. luscus), with a similar black spot at the base of the pectorals, also dark, transverse bands, and a barbel; and the Haddock (G. Æglefinus), with a black patch on either side above the pectorals, and a dark lateral line. The family also includes the Ling (Molva vulgaris) and the Hake (Merluccius vulgaris), both of which are caught in deep water; and the Rocklings (genus Motella), three species of which frequent our rocky shores.

Fig. 235.—The Snake Pipe-fish

The last mentioned are interesting little fishes that may be found on stony beaches at low tide, for they often remain under cover between the tide-marks, and may be seen on turning over stones and weeds. Perhaps the commonest of them is the Five-bearded Rockling (M. mustela), which has four barbels on the upper lip and one on the lower. It is of a dark-brown colour above, and light below, and makes nests of corallines in rock cavities. The Three-bearded Rockling (M. tricirrhata), known also as the Sea Loach and the Whistle-fish, is a larger species, sometimes reaching a length of a foot or more. Its colour is light brown, marked with darker spots, and, like the other species, it lives in the shallow water of rocky and weedy places. Another species—the Four-bearded Rockling (M. cimbria), known by the three barbels on the upper lip and one on the lower, is about eight inches long when full grown, and is found principally on the northern shores.

Our next family (SyngnathidÆ) contains some peculiar creatures called Pipe-fishes because their jaws are united into a tube. They have long and slender bodies that are covered with bony plates which form a kind of coat of mail and give them an angular form. They have very small gill-openings, a single dorsal fin, and no pelvics.

Pipe-fishes are very sluggish in habit, swimming but little, and living in the shelter of weeds and stones on rocky coasts. In fact, they are not adapted for swimming, and their attempts at this mode of locomotion are awkward in the extreme, for their bodies are rigid and the tail very small. When removed from their hiding-places they move but little, and look as much like pieces of brown or greenish wood as fishes; and their rigid bodies are so completely encased in the bony plates that they alter but little in appearance when dried, and consequently the dried specimens are often seen in museum collections.

All the British species, four in number, are small fishes, inhabiting the shallow water of rocky shores, and are often found hiding under stones near low-water mark. The largest is the great Pipe-fish or Needle-fish (Syngnathus acus), which grows to a length of about fifteen inches; and the smallest is the Worm Pipe-fish (S. lumbriciformis), which is of an olive-green colour, and has a short, upturned snout. The Lesser Pipe-fish (S. typhle), also known as the Deep-nosed Pipe-fish, is very abundant on nearly all rocky coasts, and may be distinguished from the others by having the ridge on the tail continuous with the lateral line and not with the dorsal angle. The other species is the Slender-nosed Pipe-fish or Snake Pipe-fish (Nerophis ophidium), the body of which is extremely slender, and the tail long and narrow. The male is provided with a series of small, cup-like cells, in each of which he carries an egg.

In all the bony fishes previously mentioned the fin rays are soft and flexible, and in this respect they differ from those that are to follow, for the remaining families are all characterised by the presence of one or more sharp rigid spines on the dorsal fin, and often by similar spines on other fins. They constitute the group of Spiny-finned fishes.

Of these we shall first take the prettily coloured Wrasses (family LabridÆ), which live in the holes of rocks and under the cover of weeds on rugged coasts. These fishes are very voracious in habit, and the sea angler will find that they are ready to seize almost any bait that may be offered them, and even to attack almost everything that moves within sight; but they are likely to give much trouble since they will rush into the crevices of rocks or among large weeds when hooked, and thus frequently lead to the breaking of the line.

Wrasses feed principally on molluscs and crustaceans, and are provided with extensile telescopic lips that enable them to pull the former from the rocks on which they creep, and the latter from their hiding-places among the rocks. They have also strong teeth in the gullet, by which they can crush the shells of their prey.

There are several British species of Wrasses, one of which is shown in the accompanying illustration. The commoner ones are known to fishermen and juvenile anglers by quite a variety of local names.

Fig. 236.—The Rainbow Wrass (Labrus julis)

The family GobioesocidÆ contains some small and very prettily coloured fishes of very peculiar habits, known popularly as Sucker-fishes. They have one or two adhesive suckers between the pelvic fins by which they attach themselves to rocks, stones, and shells. Some are littoral species, and may be searched for at low tide; but others inhabit deeper water, and are seldom obtained without a dredge.

Fig. 237.—The Cornish Sucker

One of the former is the Cornish Sucker (Lepadogaster cornubiensis), which may sometimes be taken in a hand net by scraping the rocks and weeds at low tide on the south-west coast. It has two suckers, each circular in form, surrounded by a firm margin, within which is a soft retractile centre. This central portion is attached to muscles by which it can be withdrawn; and a vacuum is thus produced, so that the sucker adheres by atmospheric pressure. The structure of the sucking organs can be seen to perfection when the fish attaches itself to the side of a glass aquarium, and if it be taken in the hand it will cling quite firmly to the skin.This peculiar little fish is only about three inches long, and its broad head is marked with two conspicuous purple spots, with a blue dot in the centre, and surrounded by a yellowish ring.

The allied species include the very small Two-spotted Sucker (L. bimaculatus), which is of a bright red colour, and adheres to stones and shells in deep water; the Sea Snail (Cyclopterus liparis), about four or five inches long, with a soft and slimy semi-transparent body; and Montagu’s sucker (C. Montagui), which is usually under three inches in length, and may be distinguished by its peculiar habit of curling the body laterally when at rest.

Equally interesting are the little Sticklebacks (family GastrosteidÆ), the fresh-water representatives of which are known to almost everyone. Their pugnacious habits, the bright colours assumed during the breeding season, and the wonderful nests which they build for the protection of their eggs and young, have all served to make them popular with those who take interest in the forms and ways of animals. They are, moreover, such hardy creatures that they may be kept alive for a considerable time in any well-managed aquarium.

Fig. 238.—The Fifteen-spined Stickleback and Nest

In this family the hindmost portion of the dorsal fin is soft-rayed, but the front portion is represented by a row of strong, sharp, erectile spines, which constitute a formidable weapon of offence and defence. Most of the species live in fresh water, but all the members of the family seem to be able to live almost equally well in both salt and fresh water.

We have one marine species—the Sea Stickleback or Fifteen-spined Stickleback (Gastrosteus spinachia), which may be caught on rocky and weedy coasts. It derives one of its popular names from the presence of fifteen spines along the middle of the back. Its tail is long and narrow, and its snout elongated, with the under jaw projecting beyond the upper.

The nest of this species is a pear-shaped mass of soft sea weeds and corallines, all bound together by a silky secretion, and suspended to the rock in a sheltered spot. Within this the female deposits her eggs in little clusters, all of which are bound together and to the nest itself by the silk. If the nest is damaged while occupied, it is immediately repaired, the male, it is said, taking upon himself the responsibility of this task.

Sand Smelts (family AtherinidÆ) resemble the true smelts previously described, but may be readily distinguished by the anterior dorsal fin, which is small and spinous. We have two species of this family, of which Atherina presbyter is by far the more common. It is a very pretty fish, about five inches long, with a broad silvery stripe along each side. It is very common on the sandy coasts of the south, where it also enters the brackish waters of estuaries. Young anglers catch them in considerable numbers by means of rod and line; but the professional fisherman, taking advantage of the fact that sand smelts swim in shoals, captures them in large, round, shallow nets. The net is baited with bread, crushed mussels, or offal of almost any kind, and is then lowered several feet below the surface by means of a long pole, to the end of which it is suspended. It is raised to the surface at short intervals, and will often enclose dozens of fish in a single haul.

The shallow waters of our southern coasts, including the estuaries and harbours, are also frequented by the Grey Mullet (Mugil capito), of the family MugilidÆ. This fish may be distinguished from other similar species by the four stiff spines of the front dorsal fin, and by the absence of a lateral line. The mouth is small, and without teeth, and the mode of feeding is somewhat peculiar. The food consists of worms, molluscs, and various organic matter contained in the sand or mud of the bottom. It is sucked into the mouth, together with more or less of the mud and sand, and the former is strained through a special straining apparatus situated in the pharynx.

The Grey Mullet may be taken with rod and line, and bites freely when the rag-worm is employed as bait. It is often taken in the fisherman’s drag net; but, being a splendid jumper, it frequently makes its escape as the net is drawn on the beach.

Few of our littoral fishes are so well known as the Little Blennies (family BlenniidÆ), which are to be found hiding amongst the weeds in almost every rock pool, and under stones as they await the return of the tide. Their bodies are generally cylindrical, and are either naked or covered with very minute scales. The dorsal fin runs along the whole length of the back, and each pelvic has one spine and two soft rays. When taken out of the water the gill-cavities widen considerably, and the eyeballs will be seen to move independently of each other, like those of the chamÆleon.

Most of the blennies are very active and voracious fishes, often giving considerable trouble to the angler when fishing with a rod among the rocks. They will bite at almost anything that moves, and, completely swallowing the angler’s hook, will immediately rush into a crevice from which it is often difficult to remove them.

Most of them have tentacles on the head by which they assist their movements among the rocks and stones; and some actually creep up the rugged surfaces of rocks by means of their ventral fins. They can all live for a long time out of the water, being able to retain a supply of water in their expanded gill-chambers to keep the gills moist.

Fig. 239.—The Smooth Blenny

The Smooth Blenny or Shanny (Blennius pholis) is one of the commonest species. It reaches a length of four or five inches, and has no tentacles on the head. The Eyed Blenny or Butterfly Blenny (B. ocellatus) may be distinguished by the conspicuous spot on the spinous portion of the dorsal fin. The Large Blenny (B. gattorugine) inhabits deeper water, chiefly off the south-west coast, and reaches a length of a foot or more. The Crested Blenny (B. cristatus) is named from the small crest on the head which can be raised and depressed; and the Viviparous Blenny (Zoarces viviparus), as its name implies, brings forth its young alive. The last species often exceeds a foot in length, and is found principally on the north and east coasts. The newly-born young are so transparent that the circulation of the blood within the body may be seen under the microscope quite as easily as in the web of the frog’s foot and in the tail of the tadpole.

One very common species of the BlenniidÆ differs considerably in general form from the others, its body being elongated and eel-like, but much compressed laterally. We refer to the Butterfish or Butter Gunnel (Blennius gunellus), which is often mistaken for a small eel by young sea-side naturalists. It is exceedingly common under stones at low tide, and may be recognised at once by the light rectangular spots along the flattened sides of the body. It is quite as slippery and as difficult to hold as the eel itself.

It will be interesting to note that the ugly Sea Cat or Wolf-fish (Anarrhichas lupus), which is sometimes sold for food in our large towns, is also a member of the blenny family. It is a powerful, rapacious fish—a veritable wolf of the sea, always ready to attack anything. It feeds on molluscs and crustaceans, the shells of which are easily reduced between the powerful crushing teeth that line the jaws behind the formidable canines.

Fig. 240.—The Butterfish

The Gobies (GobiidÆ) form another interesting family of small littoral fishes, easily distinguished by the fact that the ventral fins are united in such a manner that they enclose a conical cavity. The first portion of the dorsal fin has also six flexible spines. The Spotted Goby (Gobius minutus) is commonly to be found on sand-banks, where it is well protected by the colouring of its upper surface, which closely resembles that of the sand on which it rests. It is said to make a nest by cementing fragments together round some little natural hollow, or to utilise an empty shell for a similar purpose, fixing the shell to the surrounding bed, and constructing a tunnel by which it can enter or leave. The eggs are deposited in this nest, and the male keeps guard over the home. The Black or Rock Goby (G. niger) inhabits rocky coasts, clinging to the rocks by means of a sucker formed of the modified pelvic fins.A brightly coloured fish known as the Dragonet (Callionymus lyra) is sometimes classed with the Gobies, though its pelvic fins are not united. It is not a well-known species, and is seldom obtained except with the dredge, as it inhabits deep water.

Fig. 241.—The Black Goby

A peculiar little fish called the Pogge or Hook-nose (Agonus cataphractus), also known as the Armed Bull-head, is commonly taken in shrimpers’ nets on the south and east coasts. Its head and body are very angular, and are covered with an armour of keeled scales. It seldom exceeds six inches in length, and is classed with the Flying Gurnards in the family DactylopteridÆ.

Fig. 242.—The Father Lasher

The true Gurnards and the Sea Bullheads form the family CottidÆ. Several species of the former are included among our food-fishes, and are therefore more or less familiar to our readers. They are characterised by their large, square, bony heads, and by the finger-like rays of the pectoral fins which are used as organs of touch and for creeping along the bottom of the sea. The Bullheads are represented by the peculiar Father Lasher or Sting Fish (Cottus bubalis), which is very common on our rocky coasts and is frequently captured in shrimp nets. Its head and cheeks are armed with sharp spines which constitute formidable weapons of offence. When taken out of the water it distends its gills enormously; and, unless very cautiously handled, its sharp spines may be thrust deeply into the flesh. Young specimens, with imperfectly developed spines, may be seen in almost every rock pool, and the full-grown fish is easily taken with rod and line by fishing in the deep gulleys between the rocks.The remarkable Angler Fish (Lophius piscatorius), known also as the Fishing Frog and the Sea Devil (family LophiidÆ) is sometimes taken off the coasts of Devon and Cornwall; and although it cannot be truly described as a littoral species, its structure and habits are so peculiar that it deserves a passing notice. It is an ugly fish, with an enormous head, a short naked body, and a comparatively slender tail. The mouth is very capacious, sometimes measuring over a foot from angle to angle, and is directed upwards. The scaleless body is furnished with numerous slender filaments that resemble certain filamentous sea weeds, and these together with the dull colouring of the body generally enable the fish to rest unobserved on the bottom. The front portion of the dorsal fin is on the head and fore part of the body, and consists of a series of six tentacles, three long ones on the top of the head and three shorter just behind them; and the foremost of these, which is the longest, terminates in a little expansion which is kept in constant movement by the fish. The mouth is armed with rasplike teeth which can be raised or depressed at will, and when raised they are always directed backward; the eyes are directed upward, and the gill-openings are very small.

This strange creature habitually rests on the bottom of the sea, disguised by its filamentous appendages and adaptive colouring, dangling the expanded extremity of its first dorsal filament just over its upturned cavernous mouth. It does not swim much, indeed it is at the best but a bad swimmer; and when it moves it simply shuffles its heavy body along the bottom, gliding between the stones and rocks, where it may remain unobserved, its movements being produced by the action of the tail, and of the paired fins, which are better adapted for walking than for swimming. Unwary fishes, attracted by the dangling of the angler’s bait, approach the watchful monster, and while speculating on the nature of the bait, are suddenly engulfed in the capacious mouth, from which there is no escape on account of the backward direction of the teeth.

The family TrachinidÆ contains the fishes known popularly as the Stargazers and the Weavers. These are small, carnivorous species, with rather elongated bodies, terminating in tail fins that are not forked. The first dorsal fin is distinct and spinous, and the spines, as well as others that are developed on the gill-covers, are grooved for the passage of a poisonous fluid that is secreted at their bases.Our littoral species include two well-known fishes (the Greater and Lesser Weavers) that are dreaded by fishermen on account of the very painful wounds they are capable of inflicting, and the smaller of the two is also a considerable annoyance to bathers on certain sandy coasts.

Fig. 243.—The Lesser Weaver

The Greater Weaver (Trachinus draco) lives at the bottom of deep water, and is often dredged up in the trawl. Some fishermen call it the Sting Bull, and always take the precaution of cutting off the poisonous spines before disposing of the fish. It lives on the bottom with its mouth and eyes directed upward, always in readiness to seize its unwary prey, and the sharp spines of the dorsal fins are kept erect for the purpose of promptly attacking approaching foes. Its mouth and palate are armed with sharp teeth which render the escape of its prey almost impossible. The smaller species (T. vipera) seldom exceeds six inches in length. It lives in shallow water on sandy coasts, with dorsal spines erect; and the wounds it produces on the unprotected feet of bathers are often exceedingly painful on account of the injected poison, which also causes the part to swell and turn to a dark purple colour.

The remaining important families, although they contain well-known British food-fishes, do not include littoral species, and for this reason we shall pass them over with but brief notice.

The Mackerel (Scomber vernalis) belongs to the family ScomberidÆ, and is so well known that no description need be given for the purposes of identification. We have already referred to it as a beautiful illustration of protective colouring, its upper surface resembling the ripples of a deep green sea and the lower the brightness of the sky. Mackerel swim in shoals in the open sea, pursuing and devouring the fry of herrings and other fish; and in order that they may be enabled to cover enormous distances their muscles are richly supplied with blood. This not only gives a pinkish colour to the flesh, but results in a greater amount of oxidation and the maintenance thereby of a body temperature several degrees higher than that of the surrounding water. We would also call attention to the five or six small fins behind the dorsal and anal fins as characteristic of the ScomberidÆ.

Our next family (the CyttidÆ) contains the John Dory (Zeus-faber), concerning which some superstitions are still prevalent in parts. It is brightly coloured, but not graceful in form, and is often caught in large numbers off the coasts of Devon and Cornwall. Some fishermen call it the Cock, on account of the crest on the back; while others know it as St. Peter’s Fish, and will point out the impression of the Apostle’s finger on each side—a black spot surrounded by a light ring.

The Horse Mackerel (Caranx trachurus) is found principally in the same parts, where it devours the fry of other fishes. It is not a very close relative of the common mackerel, but belongs to a distinct family (CarangidÆ), of which it is the only British representative. It is a carnivorous fish, easily distinguished from Scomber by its conical teeth, as well as by the bony plates of the lateral line, the posterior of which are keeled or spined.

While the last-mentioned families contain only fishes of truly pelagic habits, the next (SparidÆ), formed by the Sea Breams, generally keep near the coast, and often enter fresh waters. In these the body is much compressed laterally, and is covered with large scales; the first half of the dorsal fin is also spinous. The Common Sea Bream (Sparus auratus), characterised by its red colour with brilliant golden reflections, and by a dark spot on the shoulder, may often be angled from rocks and piers. The young, in which the dark spots have not yet appeared, are known as Chads, and are often regarded as a distinct species. The Black Bream (Cantharus lineatus) is an omnivorous feeder, and will take both animal and vegetable baits.

The Red Mullets (family MullidÆ) may be distinguished from the grey mullets previously described by the two long erectile barbules on the lower jaw. The scales are large and thin, with serrated edges, and the front portion of the dorsal fin has weak spines. The common British species (Mullus barbatus) frequents our south and east coasts, being specially abundant round Devon and Cornwall, where they often occur in vast shoals, and the young are often to be caught in estuaries and harbours.

Our last example is the Common Bass or Sea Perch (Morone abrax), of the family SerranidÆ. It is also known locally as the White Salmon and the Salmon Dace. This fish may be taken with rod and line on rocky coasts and at the mouths of rivers. The sand-eel, or an artificial imitation of it, is commonly used as bait, but the Cornish fishermen more frequently employ a piece of herring or pilchard for the purpose. The first dorsal fin of this fish has very strong spines which may inflict severe wounds when the live creature is carelessly handled.

Omitting all mention of sea birds, for the reason previously given, we now pass to the highest division of vertebrates—the Mammals—of which we shall describe but one species—the Common Porpoise, this being the only marine mammal that can be regarded as a frequent visitor to the British coasts in general.

It may be well at the outset to understand exactly why the porpoise is classed with the mammals and not with the fishes—to see how its structure and functions correspond with those of our own bodies rather than with those of the animals dealt with in the preceding portion of the present chapter.

First, then, while the young of fishes are almost invariably produced from eggs and are not nourished by the parents, the young of the porpoise are produced alive, and are nourished with milk secreted by the mammary glands of the mother. This is an all-important feature, and is the one implied in the term mammal. The porpoise also differs from nearly all fishes in that it breathes by lungs instead of gills, obtaining its air direct from the atmosphere, and not from the water. Hence we find it coming to the surface at frequent intervals to discharge its vitiated air and to inhale a fresh supply. The body-cavity of a mammal is divided into two parts by a muscular diaphragm, the foremost division, called the thorax, containing the heart and lungs, and the other (the abdomen) the remainder of the internal organs, while the diaphragm itself plays an important part in the respiratory movement by which air is drawn into the lungs. The body of the porpoise is so divided, but no such division ever occurs in any of the fishes. Lastly, the heart of the porpoise, in common with the rest of the mammals, is divided into four cavities, and the blood is warm, while the heart of a fish has generally only two divisions, and the blood propelled by it is of about the same temperature as that of the surrounding medium. Several other important differences between the porpoise and the fish might be given, but the above will be quite sufficient to show why they are placed in different classes.Mammals are divided into several classes, and one of these (Cetacea) includes the fish-like Whales, Porpoises, and Dolphins, all of which are peculiarly adapted to a purely aquatic life. Like most of the fishes, their upper surfaces are of a dark colour, and the lower very light. Their fore limbs are constructed on the same plan as those of the higher mammals, the bones of the arm being attached to a large shoulder-blade, and the hand formed of four or five well-developed fingers which are enclosed in skin, so that they constitute a paddle or flipper well adapted for propulsion through water. There is no collar-bone, however, and the fingers have no nails or claws. There are no hind limbs visible externally, but a rudimentary pelvic girdle forms a part of the internal skeleton. A dorsal fin exists, but this is merely an extension of the skin of the back, and is not supported by either bones or rays. The skin itself has no scales, like that of most fishes, but is smooth and naked; and below it lies a large amount of fat, which, being a very bad conductor of heat, serves to prevent the escape of heat from the body.

The tails of cetaceans are also mere folds of the skin, supported in the centre by the extremity of the vertebral column; but unlike the tail fins of fishes, they are expanded horizontally instead of in the vertical plane. This latter is an important adaptive feature of the cetaceans, since the vertical movement of a tail so disposed is exactly what is required to assist the animals as they alternately rise to the surface for air and again descend into the sea in search of their food.

Among the other external characters of the cetacean we may note the nostrils, which are always situated on the highest point of the head, and are thus the first part exposed when the creature rises to renew its supply of air; also the ears, which are two small apertures behind the eye, without any form of external appendages.

The skeleton of the cetacean is formed of light spongy bones, saturated with oily matter; and although the animal has no true neck, visible as such externally, it is interesting to note that, in common with all other mammals, even with the long-necked giraffe, it possesses its seven cervical or neck vertebrÆ.

Porpoises and Dolphins together form the family DelphinidÆ, characterised by having the blow-hole in the form of a crescent with its convexity turned towards the front, and of these the Porpoises constitute the genus PhocÆna.

The Common Porpoise (P. communis) is the species that is so often seen close to our shores and in the harbours and estuaries, swimming in shoals with a graceful undulatory movement. Porpoises move forward entirely by the vertical action of their powerful horizontal tails, and extend their flippers only to change their course or to arrest their progress. At short intervals they rise to the surface, exposing their slate-coloured backs and dorsal fins for a moment, and then immediately dive downwards in such a manner as to appear to turn a series of somersaults. Occasionally they will leap quite out of the water, exhibiting their white under surfaces, which shine with a sudden flash when illuminated by the rays of a bright sun. The blow-hole is the first part exposed, and if one is sufficiently near the shoal a fountain of spray may be seen to shoot into the air, and the outrush of the expired air may be heard as each one makes its appearance.

Fig. 244.—The Common Porpoise

The true nature of the spouting of a cetacean seems to be very generally misunderstood, the fountain of spray produced at each exhalation giving the idea that the animal is expelling a quantity of water from its nostrils. This, of course, is not the case; for the cetacean, being an air-breather, has no need to take in a supply of water, as the gill-breathing fishes have. Air only is expelled through the nostrils; but as the expiration sometimes commences before these apertures are brought quite to the surface, a certain amount of water is shot upwards with the expired air; and even if the expiration commences after the nostrils are exposed, the small quantity of water they contain is blown into a jet of spray; and in a cool atmosphere, the density of this is increased by the condensation of vapour contained in the warm and saturated air from the lungs of the animal. It will be noticed, too, that the creature does not check its course in the least for the purpose of respiration, the foul air being expelled and a fresh supply taken in exchange during the short time that the blow-hole remains above the surface of the water.

The Common Porpoise measures five or six feet in length, and subsists on pilchards, herrings, mackerel, and other fish, the shoals or ‘schools’ of which it pursues so closely that it is often taken in the fishermen’s nets. Its flesh was formerly eaten in our own country, but it is now seldom hunted except for its oil and its hide. About three or four gallons of the former may be obtained from each animal; and the latter is highly valued on account of its durability, though it should be known that much of the so-called porpoise-hide manufactured is really the product of the White Whale.


                                                                                                                                                                                                                                                                                                           

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