Part 3

From worms and worm-like creatures, were developed snails and a great variety of small animals, covered with shells. The Cambrian Rocks, the earliest rocks that have preserved fossils, have yielded the remains of some of these shell creatures (Fig. 8, upper). The Upper Silurian Rocks, belonging to a period much later than the Cambrian, have entombed the fossils of the molluscs shown in Fig. 8 (lower).

We must understand that by this time living things had been evolving for millions of years, yet these shelled animals were the highest forms that had so far appeared. We must understand, too, that only the skeletons of creatures possessing a bony frame could be preserved as fossils. The fleshy part of the body, Nature destroyed. Moreover, it must be realized that of the countless billions of creatures that have lived, the rocks have preserved the fossil remains of only a few. We must not expect too much from Nature’s mutilated record. It is enough to know that the specimens that have been preserved prove the gradual unfoldment of life, and enable us to interpret the wonderful story of evolution.

There is a small animal known as the Amphioxus (Fig. 9). Standing midway between the worm and the fish, its distinguishing peculiarity lies in the fact that it has a rod of cartilage—the notochord—extending along its back, over which runs a line of nerve cells. This creature, the child of the worm and the parent of the fish, is of singular importance, since it foretells the coming of the vertebrates—the creatures with a backbone. In due time the fishes were evolved from the Amphioxus. The first fish appeared in the Devonian period, that is to say, when about one-third of the whole geological series of rocks had been formed. Fig. 10 (upper) represents a fossil of the earliest known fish. The skeleton shows a primitive form. The lower specimens represent other early fishes. Observe the curious worm-like resemblance of the middle one. There are still fishes of very unfinished form. Lampreys (Fig. 11) show, as it were, fishes in the making. They have strangely undeveloped heads, no jaws, and only a crude sucker-like cavity for a mouth.

The early fishes had no bones in their bodies. Their skeletons were composed of cartilage. Primitive fishes of to-day—sharks, rays, and others—have no bones. These fishes continue lines of descent from ancestors that appeared before the bony frame had been evolved.

Life was born in the sea; it moved from the sea to the land; and when this advance was made, it was the fishes that led the way. Some fishes developed lungs and began, tentatively at first, to live on the shore or in marshes. Life was moving towards the amphibians, and the evidence of its advance in this direction has been preserved. As the Amphioxus is the link between the worm and the fish, so lung fishes are links between the true fishes and the amphibians. Fig. 12 (at the top) shows the Burnett salmon, of Queensland—a fish with one lung; below are two mud-fishes of Africa and Brazil—fishes with two lungs. These lung fishes, or double-breathers, have the characteristics both of the fish and the frog. To scales and gills and fins and other features of the fish, they add lungs, nostrils, the beginning of a three-chambered heart, and other features of the frog. Living in regions from which the water periodically disappears, these creatures build around themselves in the dry season a shell of mud and leaves, and there, while awaiting the return of the water, they breathe air, and live on the fat stored up in their tails.

These lung fishes can walk on their fins; in fact, the fins of some of them are formed more like legs than fins.

The Flying Fish (Fig. 13) is another variation. This fish can sustain itself in the air for a hundred yards or more. Yet another curious fish that will not stay in the water is the Climbing Perch (Fig. 14). This fish may be seen crossing fields in India, and with the use of its fins it even climbs trees. These strange fishes are surely links to higher forms of life.

That the amphibian has been evolved from the fish may be seen in the evolution of the frog (Fig. 15). Number 1 shows the newly-hatched tadpoles; 2 and 2a show the branching, external gills; 3 to 8 illustrate further steps in the evolutionary process. The fish-like tail, so prominent in the early stages, is finally absorbed and we have the finished frog.

In the evolution of the frog we have a most suggestive illustration of the transformation of a creature during a single lifetime. The fish becomes an amphibian; the gilled, water-breathing creature becomes a lunged, air-breather; a water animal leaves its habitat for a home on land; a vegetable diet is abandoned for one of flesh. Truly a striking summary instance of the power of evolution!

All that man has become, all the wealth and worth of the civilization he has achieved, has been due to the fact that he has possessed a hand which could obey the command of his brain. Without a hand, without fingers, man would still be a wild beast of the forest. It was in the amphibian that Nature first produced the five divisions of the foot, which, inherited by the reptiles and then by the mammals, in the end became specialized into the human hand. The beginning of the hand is seen in the foot of the frog.

In the Carboniferous period, when the coal measures were laid down, appeared the wedge-headed amphibian, shown in Fig. 16 (above) and later, in the Permian period, the roof-headed amphibian (Fig. 16, below) was born into the world. This roof-headed amphibian is all the more interesting, for from some of these creatures were born the reptiles, from which, in turn, arose the mammals.

From the amphibians were developed the true reptiles, and these branched out into many forms. Some lived in the water, some roamed on the land, some flew in the air. In a warm climate, and where food abounded, some of these creatures, like the Ceratosaurus (Fig. 17), the Atlantosaurus and the Diplodocus, grew to a prodigious size. Some were fifty, some a hundred, some a hundred and fifty feet long; some had a hundred teeth, and eyes fifteen inches across; some weighed ninety tons, and made footprints a yard square. It was in the Mesozoic times, millions of ages ago, when these ungainly monsters were the monarchs of the earth. Happily, they have long since been extinct, and to-day their colossal, though harmless, skeletons may be studied in the museums of the world.

The wedge-headed Amphibian (above); the Branchiosaurus—the roof-headed Amphibian (below).]

From the reptiles came the birds. The first birds had teeth, claws on their wings, and bony tails of many joints (Fig. 18). The fossil remains of two of these reptile-birds—the earliest birds known—were found, some years ago, in the Jurassic limestone strata of Bavaria. These creatures had thirty-two teeth, three clawed fingers on each wing, and a lizard-like tail of twenty joints, with two long feathers growing out of each vertebra. Occupying the ground midway between the reptile and the bird, having the characteristics of both—the link between the four-legged animal and the feathered songster of the air—the Archaeopteryx, as this ancient bird is called, was about the size of a crow.

Another line of development led from the reptiles to the mammals—the hair-clothed creatures that suckle their young. This was the most promising line of Nature’s advance, for at the end of this line, man was destined to appear.

A giant reptile of the Jurassic Period.]

An amazingly curious link, which connects the reptile with the bird on the one hand and with the mammal on the other, is the Duck-bill (Fig. 19). This creature, whose home is in Australia, is covered with dense fur and suckles its young, like a mammal; but, on the other hand, it lays eggs like the reptile and the bird. The eggs have large yolks, like those of birds; are hatched by the warmth of the mother’s body; and when the young is born, it lives on milk drawn from its mother’s breast. Observe, too, that the mother Duck-bill has no nipples, but mere depressions in the breast, from which the milk oozes out among the fur, to be sucked up by the young. Think of a fur-covered, five-toed, web-footed, duck-billed, flesh-eating, swimming animal, housing itself in a burrow in the bank of a stream, being born from an egg, like a bird; formed in part like a reptile, and deriving its early sustenance by sucking the milk-ooze from its mother’s teatless breast! This link between reptile, bird and mammal, this crude combination of three forms of life, shows finished forms in the making. It is the living proof of the manner in which Nature has accomplished her work—of the steps by which evolution has advanced. It is what Darwin called “a living fossil.”

After the Duck-bills came the marsupial mammals—mammals whose young, born not yet fully developed, are carried for a time in a pouch attached to the body of the mother. The kangaroo (Fig. 20) belongs to this class. Here the advance is from an egg-laying mammal to one whose young is partly formed in the body of the mother. I say partly formed, for, although the kangaroo is as large as a man, its young, when born, though it is no larger than the little finger, is still a fœtus, so imperfectly formed that it must be carried for months in the mother’s pouch, so that it may complete its development as a babe. Meanwhile, being unable to feed itself, the mother, by an exercise of her muscles, forces milk down its throat. Once more Nature, in her forward march, is blazing a new trail. Life, by employing crude makeshifts and adaptations, is fashioning for itself a higher mould.

The lower picture shows the joints of the tail with the tail feathers.]

The marsupial mammals were followed by the placental mammals, animals whose young are nourished before birth by a disc-like organ, called the placenta—the after-birth.

The Pariasaurus Baini (Fig. 21) shows Nature, the apprentice, trying to make a quadruped. I say trying, for see what a crude, raw specimen this monster was. The best thing that can be said of this fellow is that he had his day of fighting for a place in the sun and was then supplanted by higher creatures.

Many ages of progress, during which life assumed a rich variety of forms, including the early stages of most of the hoofed animals, brought the process of evolution to the lemurs, the monkey-like creatures that make their home in trees (Fig. 22). The lemurs differ from monkeys in that the milk glands of the female are on the abdomen instead of the breast, while the index finger of each hand, and the second toe of each foot, are furnished with claws, all the other fingers and toes having flat nails. Here again is a link between the lower and the higher life. Nature is stumbling and bungling, but getting there.

After the lemurs came the Slow Loris (Fig. 23). This species of the Loris has no tail, and its front foot bears a strong resemblance to the human hand. From these creatures, or possibly from similar creatures, were evolved the true apes (Fig. 24), and from these came the anthropoid or man-like apes.

There are still in existence four genera, or kinds, of these anthropoid apes—the gibbon, the gorilla, the orang, and the chimpanzee. The gibbon (Fig. 25) shows an alert, human-like expression, which is fully borne out in his pose. The picture of a female gorilla (Fig. 26) suggests with even greater force that we have here a human being in the making. Yet this creature, be it understood, may be separated from the lowest living human being by millions of years of development. The giant gorilla (Fig. 27), shot by Paschen, in the Cameroons, differed from the ordinary gorilla in the development of the skull and in size. He was six feet, eight inches tall from the crown of his head to his middle toe; the span of his arms was six feet, nine inches; his chest measurement was twice as great as that of a strong man. Yes, a dangerous gentleman to meet!

The illustration to the right shows a young Kangaroo shortly after birth. That the creature is a quite unfinished fœtus is obvious.]

The approach to the human look on the face of the bald-headed chimpanzee (Fig. 28) is nothing less than remarkable. The form of the skull shows a decided advance towards the human. The countenance is, of course, a little open, but—well, the whole head so strongly resembles the human that he might almost be mistaken for one who believes the story of Jonah and the whale!

That man is related to the anthropoid apes becomes evident when his anatomical structure is compared with theirs (Fig. 29). While these creatures differ from one another as do the different races of men, as, for example, in the color of the skin, in the size and shape of the skull, and in the length of the arms and legs, they are all essentially man-like. And while all these creatures are like human beings in the formation of their skeletons, in their anatomical structure, and in their physiological functioning, each of them approaches more closely to man than any of the others in the development of some part of its body. Thus, “the orang approaches closest to man in the formation of the brain, the chimpanzee in the shape of the spine and in certain characteristics of the skull, the gorilla in the development of the feet and in size, and the gibbon in the formation of the throat and teeth.” Prof. Ernst Haeckel, in the “Riddle of the Universe,” sums up man’s relation to the anthropoids as follows:

This skeleton was found in the Permian Strata of South Africa.]