In some communities rabbits become such a pest that the inhabitants turn out in a body and drive them into enclosures.
adapted for certain regions as those now inhabiting them. Striking examples of this are the English sparrow and the gipsy moth, which have spread with such tremendous rapidity since their introduction into this country. The rabbit in Australia and southern California is another striking example. The adaptability of plants to a new region is also illustrated by the Russian thistle which was introduced into this country in 1873 and which has now become a national pest.
115.Life of the Sea. -The plants living in the sea are nearly all ofa low order. The mangrove trees which border some tropical shores represent their highest type. Themost abundant of sea plants, the sea- weeds, have no flower or seed or true root, although most of them have an anchoring device by which they are attached to the bottom. Their food is absorbed from the surrounding water. They have developed littlesupporting tissue, but instead have
DIFFERENT KINDS OF SEAWEED.
bladder-like air cavities or floats, which enable them to maintain an erect position or to float freely in the water. Usually they abound near the shore where the water is shallow.
The vast surface of the open sea supports few plants except the minute one-celled plants, the diatoms, of which there are many species and an almost infinite number of individuals. These furnish about the only food for the animals of the open sea except that obtained by preying upon each other.
A great quantity of detached seaweed (Sargassum), filled withmultitudes of small marine animals and the fishes which prey upon them, covers the surface of the middle Atlantic, the center of the oceanic eddy. Through this Columbus sailed from the 16th of September to the 8th of October, 1492, greatly to his own astonishment and to the terror of his crew, who had never before heard of these "oceanic meadows."A SMALL SHARK.
Photographed under water.
The animals of the sea vary in size from the microscopic globigerina, whose tiny shells blanket the beds of the deeper seas, to the whale, that huge giant of the deep, in comparison with which the largest land animals are but pigmies. Although monarchof all the finny tribe, it is not a fish at all, but a mammal which became infatuated with a salt-water life and so through countless ages has more and more assumed the finny aspect. It is obliged to rise to the surface to breathe. It cares for its young like other mammals.
Here, too, are found the jellyfish, the Portuguese man-of-war (Fig. 110), some fishes, many crustaceans, a few insects, turtles, snakes and mammals. Most of these animals are lightly built and are well equipped for floating and swimming. Some sea animals, like the oyster, barnacle and coral polyp, are fixed, and rely upon the currents of the water to bring them their food, while others, like the crab, the lobster and the fish, move from place to place in search of prey.
In the warmer seas the surface water is often filledFig. 110.
with minute microscopical animals which have the power, when disturbed, of emitting light, so that when a boat glides through these waters, a trail of sparkling silver seems to follow in the wake.
Between the surface and the bottom of the deep ocean there seems to be a vast depth of water almost devoid of life. This region, like the bottom of the ocean, has been little explored and there may be life here which has not been discovered. From the bottom of the sea the dredge has brought up some very curious forms of life. Here under tremendous pressure and in profound darkness have been developed species of carnivorous fishes.
Some of these have large, peculiarly well-developed eyes and others have not even the rudiments of eyes. As the light of the sun never penetrates to these depths, it would seem at first that eyes could be of no use to animals,but it has been found that some of the
animals of the ocean bottom have the
FLYING FISH.
Notice how the front fins have become wing-like.
power of emitting light in some such way as the glow worm and firefly do, and it is probable that it is to see this phosphorescent light that the eyes of the animals are used. There are no plants here and the life is much less abundant and less varied than near the surface.
There is but little variation in the conditions surrounding the animals of the sea, so the organs corresponding to these conditions are not diverse. Living in a buoyant m e d i u m dense enough to support their bodies, and of almost unvarying temperature,the sea animals have never
SEALS.
Originally land animals.
required or developed varied
organs for locomotion, like the wing, the hoof and the paw, or for protection from cold, like the feather, the hair, or wool. It is true that certain sea dwellers, like the seal, are covered with hair, but these air breathers were probably originally a land type and have acquired the habit of living in the water. The highest traits of animal life, such as are found in land animals, have not been required or acquired by the sea animals, and although the number of species and kinds is very great, there is not found among them the same grade of intelligence or power of adaptability, as among the land animals.
116.Life of the Land. -The highest development of both plantand animal life is found upon the land. Here at the meeting place of the solid earth and its gaseous envelope, subjected to great variations in amount of sunlight, moisture, temperature and soil, the plants and animals have acquired a marvelous variety of forms and structures to adapt them for their varied surroundings, and enable them to secure a living.
PRICKLY PHLOX.
Notice the thorns by which it protects itself.