Part 49

=Trout=, a name applied to various members of the Salmon family. The Common or Brown Trout (_Salmo fario_) varies greatly in appearance, not only with individuals but at different seasons, and this variability has led some authorities to distinguish a number of subspecies.

At midsummer an adult trout is usually brownish or olive in color, with pure white on the belly and gold on the flanks, while the back varies from olive or pale brown to nearly black. The dorsal fin and sides are spotted with black and often also with scarlet. The scales are circular, thin and minute. When the spawning season begins in autumn all the color disappears and the body becomes slimy to the touch. The head of the male is larger than that of the female, and the lower jaw bears a cartilaginous knob. It feeds on a large variety of food, different kinds appealing in turn. It is by cunning imitations of some prevailing fly that the fisherman makes his most cherished captures.

The artificial hatching of trout is now carried on extensively, and lakes and streams can be stocked or replenished with fish if they are not too polluted.

The Bull Trout or Sea Trout (_S. eriox_) most resembles the salmon in appearance and habits, though thicker in proportion to its length, and with larger and more numerous dark spots on the gill-covers and scales.

The Salmon or White Trout (_S. trutta_) is a more elegant fish, and its flesh is much more delicate in flavor. The habits of both are similar.

The Rainbow Trout (_Salmo irideus_) of America has been introduced into many parts of the world; in New Zealand, especially in Lake Taupo, it attains the greatest size, many tons being caught yearly.

=Whitefish= (_Coregonus clupeiformis_), the common whitefish, is the largest of all the American lake whitefish. It is very highly esteemed for food, ranking, indeed, as one of the finest table fishes. Its range extends from Lake Champlain to the Arctic Circle.

=CARTILAGINOUS FISHES= (_Elasmobranchii_)

These fishes have a cartilaginous, pliant, undeveloped skeleton, and are not covered with true scales. They include rays, sawfish, sharks, skates and others.

=Ray,= a popular name applied to many of the flat cartilaginous fishes: Thornbacks, Electric Rays, Sting-rays, Eagle-rays are representative. They lead a somewhat sedentary life at the bottom of the sea, moving sluggishly by undulations of the pectoral fins which form a large part of the flat body. Many attain a large size, sometimes measuring six feet across.

=Sawfish= (_Pristis_) are distinguished by the prolongation of the snout into a formidable weapon bordered on each side by sharp teeth. Some species are found off the southern coasts of North America and in the Gulf of Mexico, and in the Mediterranean and many other seas. With its saw, which is sometimes six feet in length, the sawfish slashes or rips up its prey, and its assault is often fatal to large whales.

=Sharks= are a group of very simple fishes, which have only a cartilage skeleton, no bone being developed anywhere in them. They have the gill openings on the side of the neck separate, and in all of the common species the mouth is on the lower side of the head instead of at the tip, as in ordinary fishes. The tail has unequal lobes, the upper lobe being much the larger. There are always four paired fins and one or more on the back. The size of the sharks varies from the smaller dogfish, about two feet long, to the great basking shark, some forty feet in length. Most of these species are very voracious, but the tales of man-eating are often exaggerated, although occasionally they may occur. Some of the largest species feed exclusively on shellfish. The flesh of several species is good to eat, but they are mostly neglected in America. The livers are very rich in oil, which commands a good price for use in dressing leather. In some species the skin has small spines and was formerly used (it was called shagreen) instead of sandpaper. Skin with larger plates is sometimes used in the manufacture of pocketbooks, etc.

=Skates= (_Raia batis_).--A group of fishes, closely related to the sharks, but having the body flattened from above downward, and with the anterior fins so united to the side of the head and the body that it has a rhomboid appearance and the tail seems like an inconsiderable appendage. The mouth and the gill openings are on the under surface. The animals are bottom feeders, living on clams and mussels, buried in the mud. In Europe some of the smaller species are used for food. Another has a large electric battery on either side of the head, capable of giving very strong shocks. This is called the torpedo.

=ARMORED FISH= (_Ganoidei_)

These include, among others, the Bony Pike and the Sturgeons.

=Bony Pike or Garfish.=--A remarkable genus of fishes inhabiting North American lakes and rivers, and one of the few living forms that now represent the order of ganoid fishes so largely developed in previous geological epochs. The body is covered with smooth, enameled scales, so hard that it is impossible to pierce them with a spear. The common garfish attains a length of five feet, and is easily distinguished by the great length of its jaws.

=Sturgeon= (_Acipenser_).--These large, sluggish fishes, some reach a length of over ten feet, and live on worms, crustacea, and mollusks. The body is long and narrow with five rows of bony shields. There are many species of sturgeon, all confined to the northern hemisphere. They live in the sea and great lakes, and ascend the great rivers. All supply valuable commodities, for which they are regularly captured on a large scale. These commodities are their flesh, which is palatable and wholesome, their roe (caviare), and their air-bladders, from which isinglass is made.

The most important sturgeon-fishery in Europe is that of the Volga and the Caspian Sea. The flesh of the fish is salted, and caviare and isinglass made on a large scale from the roes and air-bladder.

THE STERLET (_A. ruthenus_) is a much smaller species, which is common in the Black and Caspian Seas, and ascends the Danube as far as Vienna. It is one of the principal objects of the sturgeon fishery on the Volga.

In America sturgeon flesh is eaten fresh, and caviare is made both in Georgia and in San Francisco; but there is no great fishery in any particular district, and the manufacture of isinglass does not receive much attention. The sturgeon of the great lakes (_A. rubicundus_) and the Shovel-nose of the Mississippi valley are the chief American species.

=LUNG-FISHES OR DOUBLE-BREATHERS=

(_Dipnoi_) are at present represented by three fresh-water types, the insignificant remnant of a group that was once dominant in the sea, and would have become entirely extinct if some of its members had not taken to live in the waters of the land. These types are the eel-shaped mud-fishes of West Africa (_Protopterus_) and South America (_Lepidosiren_), and a Queensland form (_Ceratodus_). In all these the swim-bladder has been converted into a regular lung, which returns purified blood to the heart. The African form lives in streams which are liable to dry up, and were it not for the possession of a kind of lung capable of breathing air, it would perish during the dry season, whereas it remains embedded in the mud in a torpid state till the rains return.

The Queensland lung-fish lives under somewhat different conditions, for its native rivers do not entirely dry up, but are reduced to a series of deep holes connected by mere trickles of water. These holes become so foul from decaying vegetation and dead fish that the possession of a lung is a vital matter, and if the _ceratodus_ were not able to come to the surface and breathe air it would probably succumb.

_THE MOLLUSCS_ (_Molluska_)

=SNAILS, CUTTLEFISHES, SQUIDS, OCTOPUS, TUSK SHELLS, BIVALVE MOLLUSCS, OYSTERS=

THE MOLLUSCS have no limbs. The body is surrounded by a membraneous sac, from the secretions of which in many species a chalky shell is formed. The organs of circulation, digestion, and respiration are well developed. The under side of the body is thickened into a fleshy “foot,” by which locomotion is effected, and there is a well-marked head.

The Molluscs are divided into five classes: (1) Snails and Slugs (_Gastropoda_). (2) Cuttlefishes (_Cephalopoda_); (3) Tusk Shells (_Scaphopoda_); (4) Bivalves (_Lamellibranchia_); (5) Mail Shells (_Protomollusca_).

=Argonaut= (_Argonauta_) belongs to the two-gilled cuttle-fishes, and are distinguished by the females possessing a single-chambered external shell not organically connected with the body of the animal. The males have no shell and are of much smaller size than the females. The shell is fragile, translucent, and boat-like in shape; it serves as the receptacle of the eggs of the female, which sits in it with the respiratory tube or “funnel” turned toward the carina or “keel.” This famed mollusk swims only by ejecting water from its funnel, and it can crawl in a reversed position, carrying its shell over its back like a snail. The argonaut, or _paper-nautilus_, must be carefully distinguished from the _pearly-nautilus_ or nautilus proper.

=Cuttlefish.=--One of the mollusks in which there are ten arms around the mouth. The internal shell is calcified and is used as a supply of lime for cage birds. They have also an ink bag, the secretion of which furnishes the pigment sepia. Cuttle-fish are an important article of food in southern Europe.

=Octopus.=--A mollusk with a rounded body, and a small head bearing a pair of well-developed eyes, the mouth surrounded by eight long arms, each arm bearing numbers of suckers by which the animals hold their prey. Inside the mouth is a pair of jaws, shaped much like those of a parrot. Most of the species are small, possibly averaging a weight of five pounds, but some on the Pacific coast spread nearly twenty-eight feet. The octopus is eaten extensively in the Mediterranean countries.

=Oyster.=--Possibly the most valuable of all of the mollusks. There are various species in all parts of the world, but the best is the American species, which now occurs from Cape Cod to the Gulf of Mexico. Formerly it extended to the coast of Maine, and even now there are scattered beds in the Gulf of St. Lawrence. The oyster grows in shallow water, fastening its shell to some rock or shell, and in this way large beds are formed. They are also planted; that is, the young are taken and placed in favorable situations for rapid growth.

The oyster contains but comparatively little nourishment, though eaten extensively. The European oyster is smaller than ours and has a coppery taste.

Allied to the true oysters are the PEARL OYSTERS, especially abundant around Ceylon. These have the interior of the shell lined with mother-of-pearl, and when foreign particles get between body and shell they are covered with the same substance, thus forming the pearls used for adornment. These oysters are obtained by diving; the animal matter is allowed to rot, leaving the pearls behind. The shell is also of value, furnishing material for knife handles, buttons, etc., though most of our pearl buttons are now made from the shells of fresh-water mussels from the Mississippi valley.

=Scallop= (_Pecten_), a well-known bivalve, one of those with a single muscle closing the shell. The valves are fan-shaped, the left often more or less flat, the right more markedly arched; both are marked with sinuous radiating ridges, to which the name pecten (_Lat._ “a comb”) refers. The hinge-line is without teeth, and is extended laterally in two ears. The small finger-shaped foot is usually marked with bright orange or red color. The scallops are widely distributed in all seas, at depths of three to forty fathoms.

=Snails.=--A common name used for any mollusk with a coiled shell. In the narrower meaning it includes only those forms which occur on land. These land-dwelling forms have a slight shell, into which the whole body can be retracted. They feed exclusively on vegetation, which they rasp by means of a long ribbon, just inside the mouth, the surface of which is covered with thousands of minute teeth, so that the whole is a flexible file. The animal creeps about on a broad sole, and has four tentacles on the head, one pair of them bearing the simple eyes at the tip. Snails do considerable damage where they are numerous. One species is eaten by many in Europe, especially in France and Italy. Over ten thousand species are known.

The shells of sea snails are often of great beauty, and large sums have been given by collectors for specimens of unusual elegance or rarity, fifty pounds having been paid for a single example of a species of cone shell (_Conus_). The helmet shells (_Cassis_) are made up of differently colored layers, and on account of their beauty have been largely employed for the carving of cameos.

=Squid.=--A mollusk nearly related to the cuttlefish. It has a barrel-shaped body, with a head in front bearing ten pairs of tapering tentacles, each with numerous suckers. On the side of the head is a well-developed eye. Squid live largely on small fishes which they catch with the tentacles, biting them with a pair of parrot-like jaws. They are largely used as bait in fishing, and to a limited extent as food. The average length is a foot or two, but in the seas around Newfoundland and Japan giants are occasionally found with bodies a dozen feet in length and tentacles adding thirty feet to this.

=Tusk Shells= are a small group of burrowing marine forms, in which the body is covered by a long, curved shell resembling a tusk in shape. There is a small hole at its tip, through which the water which has been used in breathing makes its exit. An imperfectly developed head and a rasping organ are present, and burrowing is effected by a long foot with a three-lobed end. The food consists of small organisms, which are apparently secured by the agency of a bunch of filaments with thickened sticky tips that can be protruded from the mouth of the shell. In some respects these animals are intermediate in structure between typical sea snails and bivalve molluscs.

_JOINTED-LIMBED ANIMALS_ (_Arthropoda_)

=CRABS AND LOBSTERS, SCORPIONS AND SPIDERS, INSECTS AND GRASSHOPPERS=

This great division of the animal kingdom includes far more numerous species than any other, and is abundantly represented in both salt and fresh water, on the land and in the air. It consequently includes both _air-breathers_ and _gill-breathers_: the former, typical land insects; and the latter, chiefly crustaceous.

=CRABS AND THEIR ALLIES= (_Crustacea_)

The Crustaceans breathe by means of gills, and their bodies consist of rings. They have two pairs of feelers and two pairs of jaws, to which are mostly joined one or more pairs of jaw feet. All the remaining rings of the body may have a pair of limbs each. The head bears two pairs of feelers. Crustaceans commonly hatch out as free-swimming larvæ, like the adult in form.

This large class of jointed-limbed animals includes lobsters, prawns, shrimps, crabs, and other familiar forms, the great bulk of which are aquatic, though the wood-lice have become adapted to a life on land.

=Crab.=--In this class of Crustaceans the abdomen is small and folded under the anterior part of the body. Over two thousand species are known, differing greatly in size, shape, and in other respects. The great majority are marine, but there are a few which spend their entire life on land, only going to the water once a year to lay their eggs. The largest is the great spider crab of Japan, whose legs may stretch out a dozen feet. One species on the Atlantic coast is taken at molting time in great numbers and forms the favorite soft-shell crab of the table. The hermit crabs have the abdomen soft, and to protect this vulnerable part, they insert it in the shell of some dead snail, and carry this about with them wherever they go.

=Barnacle.=--A family of marine crustaceous animals enveloped by a mantle and shell, composed of five principal valves and several smaller pieces, joined together by a membrane attached to their circumference. They are furnished with a long, flexible, fleshy stalk, provided with muscles, by which they attach themselves to ships’ bottoms, submerged timber, etc. They feed on small marine animals, brought within their reach by the water and secured by their tentacula. Some of the larger species are edible.

=Crayfish.=--Small, fresh-water crustaceans, which resemble the lobsters in appearance. They usually live in burrows in the banks or bottoms of streams and feed on decaying animal matter. In Europe they form a considerable element in the food supply and are bred in ponds. A large number of species occur in the United States, and are always to be found in the larger markets.

=Lobster.=--The most important of the crustaceans. One species occurs on our east coast, another on the coast of northern Europe. The body is divided into two regions, the anterior bearing, besides the parts used in taking food, a pair of large pincers and four pairs of walking feet. At the front of the head are two pairs of feelers, which are sensory, and a pair of eyes on the ends of short stalks. The lobsters are fond of decaying fish and are among the scavengers of the sea. They are caught in large traps, called lobster pots, made out of lath and baited with decaying fish. The annual catch on the New England coast is estimated at about thirty million pounds, the average weight of a lobster being between two and three pounds. Farther south on our east coast, in California and the Mediterranean a different animal is called lobster.

=Prawn.=--Crustaceans nearly allied to shrimps and lobsters, but not exclusively marine. They vary in size from a couple of inches to over a foot in some tropical forms. Many of them are semi-transparent, and exhibit very fine colors. On the approach of night they change to a beautiful blue, but the meaning of this “sunset” coloration is not fully understood. Some of the deep-sea prawns are blind; others possess enormous eyes, and many emit a phosphorescent light. They may be caught in putting nets or in osier baskets, like those used for trapping lobsters. They are esteemed for eating even more highly than the shrimp.

=Shrimps.=--Small crustaceans allied to the lobster, most of them inhabitants of the sea. In many countries they form an important part of the diet, but with us they are little used with the exception of one or two southern species which are used as a basis for shrimp salad. Shrimps are very abundant off our coast and could be made an important fishery.

=SCORPIONS AND SPIDERS=

In this class of insects the head and thorax are joined together in one mass, on which they have two pairs of jaws, and four pairs of legs.

=Scorpions.=--These spider-like animals have four pairs of legs and a pair of large pincers, as well as a small pair on the anterior half of the body; while the hinder portion consists of at first a broad region, followed by a narrower one, the whole terminated with a sting, with which a poison gland is connected. The animal strikes by bending the end of this tail over the back. Its sting is very painful, but rarely if ever is it fatal. Scorpions occur as far north as Nebraska, but are more common in the tropics. They bring forth living young and care for their brood for a while.

=Spiders= have jointed bodies and legs. The bodies are divided into two regions, the anterior of these bearing four pairs of legs and two smaller pairs of appendages. The most anterior of these are the poison claws. They have a poison gland in the base, while the end of the claw tapers to a point. The front of the head has from six to eight simple eyes. The hinder half of the body, the abdomen, is without appendages, save for two or three pairs of very small projections, the spinnerets. Each of these has numbers of openings at the tip, through which a fluid is forced at will. This hardens immediately it comes in contact with the air and furnishes the silk of which the spider’s web is woven. Fine as it is, this silk is really a cable, being made of numbers of finer threads, one for each opening in the spinnerets. They use the silk for making webs, for cocoons for the eggs, nests, and in some cases for parachutes for flying. Each species makes its own type of web.

Spiders breathe by means of sacks--so-called lungs--on the lower side of the abdomen.

Our common house spider is the same as that of Europe; the largest species we see is the one found occasionally in banana bunches.

The TARANTULA has the greatest reputation from the unfounded belief that its bite causes madness which can be cured only by music. So far as is known there is only one species which can cause serious effects by biting man, and even these cases are not sufficiently authenticated.

The BIRD CATCHING SPIDER is a gigantic spider native to Surinam and elsewhere. It preys upon insects and small birds, which it hunts for and pounces upon. It is about two inches long, very hairy, and almost black; its feet when spread out occupy a surface of nearly a foot in diameter.

HUNTER-SPIDERS. A great many of this species construct no webs, but use their silk merely for lining their dwellings--which are commonly underground--or the construction of protective investments for the eggs. Such forms simply stalk their prey, seizing the victims, when near enough, by a sudden spring. One such type is the tarantula spider described above.

WATER SPIDERS are found in ponds and ditches in this country. They hunt down small crustaceans but do not construct a web. For the protection of the eggs a thimble-shaped nest is woven, moored by threads to stems or leaves, and smeared externally with liquid silk to make it watertight. The nest is filled with air brought down from the surface of the pond in successive bubbles adhering to the hairy body of the spider.

=THE INSECTS= (_Insecta_)

This ubiquitous class includes more species than all the other groups of land animals put together. The bodies consist of a series of rings, divided into three sections: the head, the thorax, and the abdomen. There is an external covering that serves as a protection. The head possesses a pair of antennæ, two large compound eyes (and sometimes several simple eyes as well), and three pairs of jaws, differing greatly in character according to the habits. The thorax bears three pairs of legs, and in most cases two pairs of wings, while the abdomen is entirely or practically limbless. The air-tubes make up an exceedingly complex system, and open to the exterior by a limited number of air-holes.

All insects undergo a series of changes (metamorphoses). From the egg first comes the larva (caterpillar, maggot); from the larva after several changes of the outer skin, the pupa is developed; from which, after a longer or shorter period of repose, the perfect insect emerges. In some, such as the dragon flies, the whole course of metamorphosis, or change, is not gone through; for in the dragon flies the larva which comes from the egg resembles the full-grown insect, only it is without wings; but later, without entering the pupa stage, it develops into the perfect insect. There are altogether about two hundred thousand various kinds of insects.