The Animal World, A Book of Natural History Part 17

THE TRUE PORPOISE

The true porpoise, or sea-hog, is much more widely distributed. It likes to tumble and gambol on the surface of the sea quite close to the sh.o.r.e.

It will ascend tidal rivers too. Its range is mainly along the Atlantic coast, and it is also found on coasts of Europe and in the Pacific Ocean. Chasing porpoises in canoes, and spearing them, is an exciting Canadian sport.

Porpoises have a curious way of swimming, for they travel along by a series of bounds, first of all leaping almost out of the water, and then diving under it. When a number of them are moving along in this way one behind the other, as they very often do, they look from a little distance just like an enormous snake winding its way through the water, and no doubt have given rise to some of the tales about the great sea-serpent.

A herd of porpoises will frequently follow a sailing ship for days, sometimes, apparently, out of pure curiosity, and sometimes in the hope of picking up something eatable among the rubbish that is thrown overboard. But they are very much afraid of steamships, and always keep at a respectful distance from them. They feed chiefly on fish, and are so quick and active that even the salmon cannot escape from them, while they will follow up shoals of mackerel and herrings and destroy them in enormous numbers.

When fully grown the porpoise is rather more than five feet long. The upper part of the body is almost black in color, becoming paler on the sides, while the lower surface is almost pure white.

THE GRAMPUS

The largest and fiercest of all the members of the dolphin family is undoubtedly the grampus, which is also known as the killer, or killer-whale. It often reaches a length of twenty feet, or even more, and is so savage and voracious that it has sometimes been called the wolf of the sea. One of these animals was once found floating on the surface of the sea, choked by a seal which it had attempted to swallow; and when its body was opened fourteen other seals and thirteen porpoises were taken from its stomach.

Three or four killers will often combine in an attack upon a large whale, leaping upon it again and again, and striking terrific blows upon its body with their tails, hanging upon its lips like so many bulldogs, biting and tearing its flesh, and often actually killing it. The whale seems terrified by the onslaught of the ferocious creatures, and sometimes scarcely attempts to resist them, apparently knowing quite well that they are sure to be victorious in the end.

The grampus is most plentiful in the northern seas, but is found now and then in almost all parts of the ocean. It occasionally visits the British sh.o.r.es. Once a living specimen was exhibited in the Brighton Aquarium, and did very well for some little time. But one day it got its snout jammed in the rock-work at the bottom of its tank, so that it could not rise to the surface to spout. And when the keeper discovered what had happened to it the poor creature was dead.

THE BLACKFISH

Almost as large as the grampus, but not nearly so savage, is the blackfish, which is so called on account of its color, for it is not a fish, being a member of the dolphin family. It is found in great shoals, generally consisting of two or three hundred animals, and often of a great many more, which are always under the guidance of a single leader.

Wherever he goes they will always follow, and they are such stupid creatures that if he swims into shallow water and casts himself ash.o.r.e, they will all swim after him and fling themselves on the beach also. In Iceland, and also in the Faroe Islands, large numbers of them are often killed, the fishermen arranging their boats in a semicircle between the shoal and the deep sea, and then driving them forward till they strand themselves upon the sh.o.r.e in their efforts to escape. Large herds have also been driven ash.o.r.e in the Orkneys and the Shetlands.

On the east coast of North America the blackfish is one of the most abundant cetaceans. Off Cape Cod more than a hundred blackfish have been seen in one school, and they are eagerly hunted for the sake of the soft oil yielded by their fat.

DOLPHINS

There are two groups of dolphins, the first of which contains three animals that live in rivers, and therefore are generally called fresh-water dolphins.

The only one of these that we can mention is the Gangetic dolphin, which inhabits the great rivers of India, and is named from the Ganges. Its chief peculiarity is that it is almost totally blind. Although the animal grows to a length of seven or eight feet, and is bulky in proportion, yet its eyeb.a.l.l.s are no larger than peas, while the nerves of sight are so imperfect that it is quite possible that it may not be able to see at all. This is no deprivation to it however, for the rivers in which it lives are always so thick with mud that even if it had properly developed eyes it would be quite unable to use them.

The Gangetic dolphin is very seldom seen, because when it comes up to breathe it only raises just the blow-holes above the surface of the water. For the same reason, we know very little indeed about its habits.

But it seems to feed on fresh-water shrimps and mollusks, and also on certain fishes which lie half-buried in the mud at the bottom of the water, rooting about for them with its snout after the manner of a pig.

This animal is often known as the susu.

SEA-DOLPHINS

Of the sea-dolphins we can only notice two. The first of these is the common dolphin, which is found in great numbers in almost all parts of the temperate and tropical seas. Apparently it is not often to be found on American coasts, but it has been captured in eastern harbors. It generally lives in herds, which will follow ships for hours together, leaping and gamboling on the surface of the sea, and yet keeping pace with the vessel without the least apparent effort. It feeds on fishes, to capture which, and hold them firmly, it has one hundred and ninety teeth, so arranged that when the mouth is closed the upper and lower ones fit in between one another like those of a steel trap and hold the prey in a grip from which there is no escape.

A full-grown dolphin is usually about seven feet long, but much larger specimens are occasionally found. The color is dark gray or glossy black above, and almost pure white on the lower parts of the body.

The bottle-nosed dolphin is a rather smaller animal, with a shorter and more pointed beak shaped rather like the neck of a bottle, and is purple black above and grayish white below. Its range is on the North Atlantic coast from Maine to Florida, on the Gulf coast, and also on some of the coasts of Europe.

MANATEES AND DUGONGS

There is just one other family of water-mammals which it will be convenient to mention here, although they do not really belong to the whale tribe. These are the very curious creatures known as sirenians, the best known of them being the manatee and the dugong.

Of course you have heard of mermaids, those imaginary creatures of the sea, which were supposed in days of old to combine the head and body of a woman with the tail of a fish. Well, very likely stories of them were told in the first place by some traveler who had seen a manatee, for the animal has a queer way of raising its head and the upper part of its body almost upright out of the water and cuddling its little one in its flippers, so that from a little distance it really looks something like a human being with a child. But at close quarters the comparison would not be a very flattering one, for there is a kind of disk-like swelling at the end of the snout, and the skin is black and coa.r.s.e and wrinkled like that of an elephant.

Manatees are found on the west coast of Africa, and also on the sh.o.r.es of South America, living near the mouths of the larger rivers. They never seem to leave the water of their own accord, and if by any chance they find themselves upon dry land, they are perfectly helpless, and can only roll over and over. One specimen seen in a zoo was quite a small animal, and had to be fed with milk out of a baby's bottle, while the keeper nursed it upon his knees. When it grew a little bigger it became very playful, and would tumble and roll about in its tank almost like a dolphin or a porpoise. And more than once it even succeeded in knocking its keeper into the water.

Another of these animals, caught at the mouth of the Essequibo River, lived in an aquarium for sixteen months. It was about eight feet long, and its tail was so powerful that every one was afraid the sides of its tank would be broken in by its tremendous blows. Its appet.i.te was remarkably good, for it used to eat as much as eighty-four pounds of lettuces every day.

There is a species of manatee, also called sea-cow, formerly ranging the South Atlantic and Gulf coasts of the United States, but now seen only in the rivers and lagoons of southeastern Florida, where it has become so rare that the State prohibits its wanton destruction under penalty of a heavy fine.

The dugong is found on the east coast of Africa, and also on the coasts of Mauritius, Ceylon, the islands of the Indian Archipelago, and Western Australia. In many respects it is very much like the manatee. But it has a forked tail instead of a rounded one, and its body is bluish black above and whitish below. It lives in shallow water near the mouths of rivers, feeds on various water-plants, and is said to be so affectionate that if one of a pair is killed the other cannot be induced to leave the dead body, but will remain by it and allow itself to be slaughtered also.

Not very many years ago dugongs were found in large herds, sometimes consisting of two or three hundred individuals, and were so tame that they would even permit themselves to be touched without attempting to escape. But they have been killed in great numbers for the sake of their hides and a valuable oil which is extracted from their bodies, so that nowadays it seldom happens that more than two or three are seen together.

A full-grown dugong is generally from seven to eight feet long, and measures about six feet round the body. The Australian dugong is said to attain a length of fourteen feet.

CHAPTER XIV

THE RODENT ANIMALS

The group of the rodents is the largest of all the tribes of mammals, for it contains more than a thousand different animals. Indeed, nearly one third of all the mammals in the world belong to this very important division.

TEETH OF THE GNAWERS

The word rodent signifies gnawing, and is given to these creatures because their front teeth are specially formed for the purpose of gnawing hard substances. You know, of course, how long and sharp the front teeth of a rat or a mouse are, and how easily these animals can nibble their way through a stout piece of board. Well, all the rodent animals have these teeth formed in just the same way. And when we come to examine them we find that they are beautifully suited to their purpose.

You would think that as they are so constantly in use, these teeth would quickly be worn down to the gums, wouldn't you? Ours would, if we employed them in the same way. But then, in the rodent animals, these teeth never stop growing, so that as fast as they are worn from above they are pushed up again from below.

Sometimes this fact leads to a very singular result. It happens now and then that a rodent animal meets with an accident and breaks off one of its front teeth. Now these teeth, remember, cannot be used unless they have one another to work against, just as the blades of a pair of scissors cannot be used unless they have one another to cut against. So, you see, when one tooth is broken short off, the opposite tooth in the other jaw becomes useless. It has nothing to work against. So it is no longer worn away from above. But of course it still goes on growing.

So before very long it projects in front of the other teeth. Still it continues to grow, and in course of time its natural curve brings it round in a semicircle, with the point toward the face. And at last, if it is a lower tooth, it pierces first the flesh of the forehead and then the skull beneath it, and enters the brain and kills the animal; while, if it happens to be an upper tooth, the point curls round under the chin and at length prevents the poor creature from opening its mouth, so that it dies miserably of starvation! It seems impossible, doesn't it? Yet in museums there are skeletons of hares and rabbits which have been killed in this singular way by one of their own front teeth.

HOW THE TEETH ARE KEPT SHARP

One would think that the edges of the teeth, at any rate, must soon be worn away. Nature has guarded against this danger by making these teeth of two different substances. The face of the tooth is made of a very thin plate of hard enamel, the rest of the tooth of much softer bone.

During use, of course, the soft bone is worn away very much faster than the hard enamel, and so the sharp, cutting edge is preserved.

It is interesting to find that we make our chisels in a very similar way. The blade is not a solid piece of steel, of the same quality throughout; it consists of steel of two different qualities. The face of the tool is a very thin plate of extremely hard steel, but the rest is of much softer metal. And as it is with the rodent's tooth, so it is with the chisel. The soft metal is worn away during use much faster than the hard, so that the edge is not destroyed.

Only two pairs of front teeth are developed in the rodent animals, and as the "eye" teeth are wanting there is always a gap in each jaw between these and the grinders.

THE COMMON SQUIRREL