Specific Nature of Life. 225 As to the specific nature and continuance of life, the best arguments are facts given by accurate observers :-" It has been deemed no mean result of comparative anatomy to have pointed out the analogy between the shark's skeleton and the human embryo, in their histological conditions; and no doubt it is a very interesting one." This analogy is not inconsistent with the observed tendency of offspring to differ from the parent; nor with the stranger fact—“This tendency and its results are independent of internal volition and external influences." Thus we are led to the great truth-" Every species is such ab initio, and takes its own course to the full manifestation of its specific characters agreeable with the nature originally impressed upon the germ. A perch, a newt, a dog, a man, do not begin to be such only when the embryologist discerns the dawnings of respective specific characters. The embryo derived its nature, and the potency of self-development according to the specific pattern, from the moment of impregnation; and each step of development moves to that consummation as its end and aim." "An orderly succession according to law, and also progressive or in the ascending course, is evident from actual knowledge of extinct species;" but none can say why circulation in the embryo of lizard, of fowl, of beast, is like a fish in its simplicity, but far from being identical. "It is proved that no germ, animal or vegetal, contains the slightest rudiment, trace or indication of the future organism-since the microscope has shown us that the first process set up in every fertilized germ is a process of repeated spontaneous fissions, ending in the production of a mass of cells, not one of which exhibits any special character; there seems no alternative but to conclude that the partial organization at any moment subsisting in a growing embryo, is transformed by the agencies acting on it into the succeeding phase of organization, and this into the next, until, through ever increasing complexities, the ultimate form is reached." The fact is established, the operation of deri1 66 Anatomy of Vertebrates," vol. i. p. 245: Owen, 8 5 2.66 Anatomy of Vertebrates," Intr., p. xxxv. : Owen. Owen : Anatomy of Vertebrates," Intr., p. xxi. Р vative secondary causes is due to a great master Principle: by whose will and power the waters swarm with swarms of living things, and birds fly above the earth : "Young fresh blood.. Keeps ever circulating still In water, in the earth, in air, In wet, dry warm, cold, everywhere Germs without number are unfurl'd."-Faust. Living beings possess at least six leading characteristics. 1. Assimilation-the power of taking in external materials, and converting them into substances for building up fresh tissue and repairing waste. By this a living body grows. 2. Alteration-certain periodic changes, in definite order by which they lose portions of their substance and die: partial death is the accompaniment of all life. 3. Reproduction-living bodies have, directly or indirectly, the power of giving origin to germs which develop into the parent's likeness. 4. Motion-every living body is the seat of energy, by which the inertia of matter is overcome; is master of physical forces; and this power in man, wielded by intelligence, brings the dead matter of the universe into obedience. 5. The life of all living beings seems to reside in a substance termed "protoplasm," or "bioplasm," differentiated more or less, which bears to it about the same relation that a conductor does to the electric current; but in no way possesses life as an inherent property. 6. The great majority of all living beings are organisedthat is possess organs or parts which perform functions. Do not live because they are organised, but are organised and have structure because they live. There is something in the action and nature of vital energies different from anything observed in physical: for it is not organism which gives life, but life which causes organism. As there are six leading characteristics of life, so are there six different types of animal structure. At first sight we suppose that every kind of animal has its own peculiar plan; we do not imagine that a lobster and a butterfly are built upon the same type, yet they really are: all known animals spring from Types of Animal Structure. 227 this unity; and, in spite of their great and many outward differences, are arranged into six kingdoms. 1. PROTOZOA (πpuros, first (ov, life), Are generally of a very minute size, composed of a nearly structureless, jelly-like substance. Animalcules, sponges, infusoria. They are not definitely segmented, have no nervous system, no digestive apparatus - beyond, occasionally, a mouth and gullet. The simplest, called monera, are small living corpuscles; nothing more than a shapeless, mobile, little lump of mucus or slime. Take a rhizopod: from the outside of this creature, which has no limiting membrane, numerous thread-like processes protrude. Originating from any point of the surface, each may contract again and disappear; or touching some fragment of nutriment, draw it, when contracting, into the general mass-thus serving as hand and mouth. This structureless body may join and become confluent with its fellow bodies; and, in brief, is at once all stomach, all skin, all mouth, all limb, and all lung. 2. CŒLENTERATA (xoλog, hollow; repov, intestine). Sea anemones, corals, sea jellies, sea firs. Most of them rise considerably above the protozoa in organization. They have a body-wall composed of two principal layers, an intestinal cavity, and a mouth leading into it. They have no organs of circulation, no nervous system-or but a rudimentary one; the mouth is surrounded by tentacles arranged in a star-like manner. The common hydra is commonly taken as a type of the lowest division. It can live when the duties of skin and stomach have been interchanged by turning it inside out. 3. ANNULOIDA (annulus, a ring; ɛidos, form). Sea-urchins, starfishes, land-stars, some internal parasites, as the tape-worm, with some minute aquatic creatures. The digestive canal is completely shut off from the cavity of the body; there is a distinct nervous system; a system of branched water vessels, usually communicating with the interior; the body of the adult, often "radiate," is never composed of a succession of definite rings. 4. ANNULOSA. Animals with bodies composed of numerous segments or rings; and nervous system, forming a knotted cord, along the lower surface of the body. Worms, leeches, crabs, lobsters, spiders, scorpions, centipedes, insects. 5. MOLLUSCA (mollis, soft). Shell-fish, snails, cuttle-fish, nautilus. Soft bodies, hard shells; no distinct segmentation of the body; and a nervous system of scattered masses. 6. VERTEBRATA. Animals with a vertebral column. The body composed of definite segments, arranged longitudinally one behind the other; the main masses of the nervous system are placed dorsally. The limbs are never more than four in number. Fishes, amphibians, birds, mammals, man. These modern classifications, with man at their head, are very simply arranged in the Divine account of the genealogical tree. We have moving creatures in the water, and creeping things on land; animals of length, birds, beasts, cattle, and man. Marine life, first created, is represented by the earliest fossils; and in the order of creation-plant, fish, bird, mammal, one generation hands a lamp of higher life to the next. To mark off the groups simply as beasts, birds, fishes, creeping things, is to make their differences of appearance, modes of life, and relative importance conspicuous. Creative energy, we may be sure, did not act by breach of natural law, but with power put forth uniformly; and in plant, fish, bird, mammal, there may have been no perceptible difference in their dawn of existence. They were not introduced collectively, or simultaneously; but at different periods in the day of life; and the earliest possessed characters in combination such as we now-a-days find separately developed in different groups of animals. It is pleasant to have the kinship of all things authoritatively stated the water brought forth, and the earth brought forth; the vegetable had seed in itself, and the animal possessed life after his kind. Not only are all living animals reducible to five or six fundamental plans of structure; but amongst the vast series of fossil forms not one has yet been found with peculiarities entitling it to be placed in a new subkingdom. The animals belonging to the sub-kingdoms are The Process of Life. 229 framed upon the same fundamental plan of structure, and are also arranged in a series of groups. All the shell-fish, for example, are built upon a common plan—a plan representing the ideal mollusc. In the kinship is individuality, and in the unity diversity. Every life possesses its own life. The primordial germs are essentially different, and tend toward the vegetable, or toward the animal, by such different lines that no plant becomes animal, no coral turns star-fish, no worm grows into leech, no cockle transforms into cuttle-fish. There are organisms with vital action not more lively than that of drops of oil fusing themselves together when they meet, and they attain no higher existence: fuse millions together yet no other animal is formed. Trace the Process of Life. All organisms arise out of structureless living matter, which in the primal state was not living at all. The essential principles of every change, or the active and moving part, no one knows how nor whence they come, enter and reside in the matter itself; and work, for the most part, from within. The earliest stages of organisms possess the greatest number of similarities. Somewhat further on, the characters are those belonging to a smaller number of organisms. At every advance, traits are acquired which successively distinguish group from group, and are finally narrowed into the highest species of finished structure. Thus were produced many varieties or species: creatures being modified by circumstances for circumstances: heredity and adaptation being the two great agents in influencing the mystery and variety of the living world of forms. In the finished structure of most advanced life we still find the same original or rudimentary matter out of which all organisms were created, and with which all are now built. Not only so, the screws, fastening the parts; the levers, raising them to a higher state; the pulleys, drawing them together; and the joints, knitting several limbs into one body; are constructed on common patterns. This fact, proving unity in the underlying energy, is a sparkle of the great truth that rules the universe: for example, the hydrogen atoms in the sun and planets vibrating |