RELATIONS OF ANIMALS AND PLANTS.

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the country for primitive man, and give to civilized man no small store of wealth.

That the vegetable and animal kingdoms form the two harmonious sides of one system of life is, finally, noticeable in this, that the life force in animals uses the oxygen of the atmosphere as the chemical agent for preparing its building material and rejects carbonic acid gas; while in vegetables the contrary is true, oxygen being rejected and carbonic acid gas being stored in the form of woody fibre.

CHAPTER VI.

ANIMAL LIFE IN THE VALLEY, ANCIENT AND MODERN.

The Life Force gained many and important ends in the comparatively narrow limits of the Vegetable Kingdom. In the plan of animal life several principles appeared that vastly raised this class in the scale of being, and left open the most wonderful possibilities to progress. In the very lowest animals there was a feeble dawning of a new individuality in sensation, in intelligence, and in the power of self-control. At the first there was but the faintest glimmer of these, and sometimes they were not all united in the same animal. It is sometimes very difficult to tell whether a structure is vegetable or animal, so slight is the space that separates the most sensitive organization among plants from animals having the least vitality.

But sensation was to be gradually developed until it became exquisitely perfect in the elaborate nervous system of the highest sub-kingdom of animals; the capacity of self-motion was to increase into the most remarkable powers of voluntary physical force; and intelligence was to ripen until most phases of the supreme mental attributes and capacities of man had been shadowed forth more or less completely, though in every case fragmentally and in limited development; and, finally, by a vast leap, all these qualities of intelligence, freed, as to the race at large, from definite limitations, were to be concentrated in the Ideal Animal.

There is a world of suggestive mystery in the gradual development of the animal frame until some of the animals came to possess physical parts closely resembling man's; and a still greater mystery is the instinct and intelligence so like, and so

cease.

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unlike, man's bestowed on the different classes of animals. In each animal these higher gifts are very perfect so far as the special ends of its life can be served by them. There they A single strongly marked quality belongs to each race with all the intelligence necessary to a successful career in such a character. There the resemblance ceases. The animal has no such reserve of unused powers and unlimited capacity of development, in a thousand ways, as are seen in man. There is a breadth and reserve of force in the higher qualities of the man that destroy the idea of his true and close relationship to the animal world. The most intelligent animal has but the shadow of the man's mental compass outside the range of its physical instincts. It is often a dense shadow, but, in the end, is nothing more. What mystery of origin and destiny lies behind these real physical, and instinctive and shadowy mental, relationships? What is man that immeasurable geological time should labor so strenuously and constantly for him, and that all organized nature should bear the broken and shadowy fragments of his image?

There are five great types or divisions of animal life, regarded as to the plan of their physical structure-Protozoans, Radiates, Mollusks, Articulates and Vertebrates. The first four are called Invertebrates. Most of the larger and more important and perfect animals belong to the last class-Vertebrates. The lowest class, Protozoans, are very simple, almost formless and jelly-like in structure, with no nervous system, often no mouth or stomach or permanent limbs. Whenever these are required they are extemporized for the occasion. They are usually extremely minute. They are commonly inclosed in a shell, and the substance of the animal is protruded to secure food. The lowest class of these are believed to have been introduced the first of all animals, although the absolute proof seems, as yet, wanting.

The Radiates are formed on the plan of a flower, similar parts spreading from a common center. They are very often

permanently attached to the sea bottom, or rocks, brilliantly colored, of most graceful forms, and must have caused the early sea bottoms, when they were most numerous, to resemble a flower garden. Many of the corals were radiate. Most, though not all, were inclosed in some kind of shell. They were extraordinarily numerous in ancient time, and their shells contributed very largely to the making of limestone rock. They had, for the most part, no nervous system, and their mouths were surrounded with tentacles, or a kind of claw, with which they seized their food.

Mollusks are soft-bodied animals, with a nervous system of scattered masses. The oyster is a Mollusk, a shell being essential to the protection of the soft baggy body. They often had various appendages, serving as arms or feet. They are very numerous in the Palæozoic rocks.

Articulates are jointed animals. Crabs, worms, and insects are of this class. The joints are in the skin or covering, the internal cavities extending continuously through all the joints. The nervous system is below the stomach and other cavities, but has a ganglion, or bunch, in each segment. Articulates have constantly increased in numbers from their first appearance to the present time.

Vertebrates have a jointed internal skeleton with a continuous cavity through the bones of the back, for the large nervous cord, and other cavities for the various instruments of a highly organized life below or in front of it. In the vertebrates the head is carefully elaborated and with more pains as the animal rises in rank until, in man, it fully dominates and controls the whole body, which is kept as erect as a tree on a very narrow base, yet with admirable powers of locomotion. There are four classes of Vertebrates-Fishes, Reptiles, Birds and Mammals. Fishes are the lowest class and have no lungs, air bladders supplying their place, and, as well as reptiles, are cold blooded; but reptiles usually have lungs-except one division of them, which has the air bladder in early life and

THE INTRODUCTION OF SPECIES.

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lungs at a later period. Birds and mammals are all warm blooded and of a higher style of structure and vital organization.

Protozoans, Radiates, Mollusks and Articulates were introduced in very early geological times, and, as it would seem at the first glance, nearly together; but there is much reason to believe that the first species whose stony structures have been preserved in the lowest Paleozoic rocks were preceded by a long series of species lower in rank, and whose fragile. shells could not be preserved in the metamorphic rocks, or those which were very much transformed by the great heat and the active chemical forces of the earlier times. Much limestone was found in those periods, which, probably, as in later times, was composed chiefly of animal shells, and a part of the carbon found in great quantity in various forms in the Azoic rocks is thought to have been produced, partly, at least, by the oily parts of animal bodies.

The first animal forms distinctly preserved were of the lower classes, but not from the very lowest families, and not usually the lowest species in their respective families. There is, however, no real exception to the rule that a steady general progress in the rank of animal forms is found in the rocks, from the lowest that contain them at all to the highest. The forms found in any system of rocks are higher in organization than in the system of rocks next below, and not so high as in the system that follows. All these, and various other observations, furnish fairly good ground for thinking that animal life was probably introduced by its simplest forms which have not been preserved.

Twenty thousand species from the Palæozoic rocks have been described. It is probable that large numbers will yet be added, and that multitudes were too slight in organization to be preserved, or too unfavorably located to become known to us. Yet, a general impress was so distinctly given to the whole life of each age by the marked features belonging to it