Stories of the Universe: Animal Life Part 9

The five chief groups of existing reptiles are the Chelonia (Tortoises and Turtles); the Rhyncocephala, represented only by _Hatteria_, a lizard found in New Zealand; the Lacertilia or Lizards; the Ophidia, or Snakes and Serpents; and the Crocodilia.

Perhaps the most interesting point regarding the reptiles that can be mentioned in brief s.p.a.ce, is the fact that they present traces of a median third eye, which have been described by Baldwin Spencer, in the New Zealand Hatteria, and in other reptiles. It is situated on the roof of the brain. While the structure in Hatteria shows it to be an eye, its position corresponds with that of the pineal gland of vertebrates generally; so that we find, in fact, the trace of a third eye in all vertebrates, including ourselves. It is, however, a trace only. In the Lamprey fishes as well as in _Hatteria_, it reaches a further degree of development. This pineal eye has been compared in structure to the eye of Ascidians.

The Birds, excluding the extinct form with teeth and a jointed tail, to which the group name of Archaeornithes is given, fall into two groups. These are the Rat.i.tae, or Birds with Raft-like, _i.e._ flat, breast-bones, and the Carinatae, or Birds with keeled breast-bones. The former include the African Ostrich (_Struthio_), the American Ostrich (_Rhea_), the Australian Emu, the Ca.s.sowary of New Guinea, and the Kiwi, or Apteryx of New Zealand; all of them birds that cannot fly. The vast majority of birds belong to the Carinatae, characterised by the projecting keel (Carina) in the middle of the breast-bone. The presence of this, which affords a safe attachment for strong muscles, is a.s.sociated with the power of flight. It is impossible to treat the birds more fully in the s.p.a.ce allotted to this little story, but a few words about feathers, however, may find a place here.

The colour of feathers is a subject of much interest. Everyone is familiar with the brilliant tints often presented by the feathers of birds, and everyone who is a close observer of natural objects knows that there are some feathers which are iridescent, changing colour according to the direction in which light falls on them. It has been shown by Dr. Gadow that this variation of the colour of a feather is due to its structure; this may be described as prismatic, for the small divisions of the feather present acute angular edges, which reflect the light like the edges of a prism. These are symmetrically repeated all along the feathers, so as to reflect the same colour throughout. Thus in the plumage of the common red and green parrot, we see feathers that are red when held in one position, and yellow when shifted to another position; while there are also feathers that are blue when seen in one position, and green when seen in another; the alternative colour being the one next in order in the rainbow.

Another point regarding the colours of feathers has no doubt puzzled many of our readers; and that is, the metallic quality of the colouring in some exceptional feathers, and in these only. The feathers of the parrot just referred to, are, for instance, simply red and yellow, or blue and green; but the feathers of the peac.o.c.k, though displaying the same colours, show a metallic l.u.s.tre which is wanting in the other case.

The feathers of the starling, the blackbird, and the black hen of the farmyard, though not so brilliant as those of the peac.o.c.k, are the same as regards the quality of the light they reflect. The secret of the difference lies in the greater opacity of the feathers named; they are _black_ feathers, while those of the parrot are light-coloured. Now after the metals themselves, there are few objects in nature so opaque as the black pigment of a black feather. If a thin section through the roots of young black feathers is cut for examination under the microscope, the pigmented parts, although cut so very thin, appear completely opaque. And just as a gla.s.s gives a better reflection when backed by something opaque, so does the reflecting surface of the feather. Hence it is that the quality of the colours reflected by these feathers is what we call "metallic." If we ask for a definition of this metallic brightness, other than the accepted fact that it resembles the light reflected from metals, the artist will reply that it consists in two things--(1) the greater brilliancy of the light reflected, that is to say the greater completeness of the reflection; and (2) the entire absence of those gradations of light which are afforded by the reflections from any object, however dark, that possesses a surface translucent, even in the smallest degree. "Metallic" reflections, in fact, may be defined as those in which the greatest amount of light is reflected, and the reflected sunlight receives from the reflecting surface the least possible degree of modification. While the actual tint of the colour reflected by a black feather, then, is determined by the form and position of its angular ridges, the quality of the reflection is determined by the opacity of the substance itself. It is interesting to note that the opacity necessary for reflecting a "metallic" l.u.s.tre, may be produced by means of pigment, in the vegetable as well as in the animal organism; for instance, in the dark centres of _Coreopsis_ (the Beetle Flower), and several other fashionable garden plants belonging to the Compositae or Daisy family. Within the animal kingdom, we may note that the metallic l.u.s.tre is almost entirely confined to land animals; their dry skins have more chance to develop opaque parts, than the moist tissues of creatures that live in the water. The most familiar exception to this rule is the Sea-Mouse, an Annelid worm found on English coasts (p. 73), which receives its odd name because it is a fat oval creature, covered with bristles, thus greatly differing in appearance from most worms. The larger bristles, which are of a dark purplish-black colour, have a bronze or golden metallic l.u.s.tre. Various other annelids exhibit brilliant rainbow colours; for example, _Nereis_, the Rainbow Worm, also found on English sh.o.r.es; but without the underlying black opaque pigment, the reflections from the surface fall short of absolutely metallic brightness. On land, we see among the insects innumerable forms which present a metallic l.u.s.tre, the beetles being the most notable in this respect. To return to the vertebrates, from which we started, everybody must have noticed that the fur of a clean well-kept black cat, when lit up by the bright sunlight in which the animal loves to bask, shows little rainbow reflections of red and green. These are due to the presence of little grooves and irregularities on the surface of the hairs, which play the same part in breaking up the light which they reflect, as do the sharp angles of iridescent feathers. Like the iridescence of the Rainbow Worm, they fall short of absolutely metallic brightness; the fault in this case being due not to the nature of the underlying stratum, so much as to the incomplete development of the light-reflecting grooves. Yet this instance serves to show the part taken by the dark pigment; for while the play of colours is perfectly obvious in the fur of a black cat, it is almost impossible to distinguish it in the case of cats with fur of lighter shades.

The Mammalia, or animals that suckle their young and produce them by birth, were formerly considered to be sharply defined from animals that lay eggs, such as the birds and reptiles. But in 1884 Mr. Caldwell confirmed the statement which had been made previously, yet hardly credited by the scientific world, to the effect that the lowest form of mammals lays eggs. This, the Duck-Mole or _Ornithorhyncus anatinus_ (Bird-billed animal much like a goose), is a native of Australia and Tasmania. It lives on the banks of rivers, and burrows in the bank. It has webbed feet, and therefore sometimes receives the name of Platypus (flat-foot). It lays eggs two at a time, in its burrow; and these eggs, like those of other egg-laying vertebrates, have a yolk.

A kindred form, _Echidna hystrix_ or Spiny Ant-eater, is found in Australia, Tasmania, and New Guinea. The _Echidna_ hatches its young in a temporary pocket, which appears in the neighbourhood of the b.r.e.a.s.t.s, and disappears after the young are old enough to take care of themselves. The _Ornithorhyncus_ has fur, the _Echidna_ has spines, with hairs between them. Neither bears the slightest resemblance to a bird; the comparison suggested in the name of _Ornithorhyncus_ is fanciful, and depends chiefly on the flat beak-like mouth; these egg-laying quadrupeds may, however, be reasonably brought into comparison with Reptiles. Neither of them has any teeth; the _Echidna_ has no teeth at all; the _Ornithorhyncus_ loses them at an early stage of growth, and develops instead hard h.o.r.n.y patches in each jaw. With these it crushes its food, which consists of small insects, worms, etc. The _Echidna_, on the contrary, lives in rocky places, and feeds on ants, which it searches for with its long-pointed snout. These two genera are grouped under the name of Prototheria or Primitive Mammals.

The pocket in which _Echidna_ hatches its young, suggests a relationship with the next group, the Metatheria or Marsupialia, which are the characteristic mammals of Australasia. These are distinguished by the possession of a permanent nursery-pocket, the "marsupium." In this they put their young, which are born, like those of other mammals, not hatched from eggs like those of the last group. They are, however, born in a very backward condition, and therefore require to go through a further period of incubation, so to speak, in the marsupium. Here each one attaches itself to a teat, to which it remains fixed. But it cannot suck as a new-born kitten or puppy does; and the milk is forced down its throat by the muscles of the teat.

[Ill.u.s.tration: FIG. 45.--Skull and Lower Jaw of Great Kangaroo, _Macropus giganteus_, much reduced.]

The Marsupialia are not entirely confined to Australasia; a few occur in South America, and in North America they are represented by the "'possum," _i.e._ Opossum, of American stories. The Marsupials seem almost to mimic the forms of ordinary quadrupeds. Thus _Notoryctes_, a form discovered a few years ago, mimics a mole. The fact is that, just as among the Eutheria, or higher mammals, special types have become established, possessed of certain habits, and especially of certain habits with regard to food, and modified in accordance with those habits. Thus there are among them savage carnivora, harmless herbivora, and rodents; and these respectively share certain characteristics in common with the carnivora, herbivora, and rodents, belonging to the Eutheria. One of the herbivorous marsupials is the Great Kangaroo, _Macropus_. It gets its name, Large-foot, from the size of its hind-paws; on these it stands, and by their aid it takes remarkably long leaps. Its skull is shown in Fig. 45; this, however, has not the full set of teeth, some of which are soon shed. It crops the herbage with its front teeth, and grinds it with its back teeth, like other herbivora.

[Ill.u.s.tration: FIG. 46.--Skull and lower jaw of Rodent; _i_, _i_, incisor teeth, separated by a long interval from the molars. About one-half the natural size.]

The study of the teeth is of great help in the cla.s.sification of the Mammalia. Of the eight orders of the Eutheria, two alone, the Sloth order and the Whale order, show a tendency to the suppression of the teeth. Those of the herbivora and carnivora may easily be compared by anyone, in the sheep and the dog respectively. Fig. 46 shows the skull of a Rodent, with elongated front teeth, adapted for that persistent gnawing which makes the animals of the order, such as the Rat and Rabbit, so terribly destructive.

TABLE SHOWING THE CLa.s.sIFICATION OF THE MAMMALIA

{ 1. PROTOTHERIA, or EGG-LAYING MAMMALS.

{ One order, the MONOTREMATA.

=MAMMALIA.= { { 2. METATHERIA, or MARSUPIAL MAMMALS.

{ { 3. EUTHERIA, or HIGHER MAMMALS.

The Mammalia are a terrestrial group. Exceptions are the Cetacea (Whales), Sirenia (Dugongs), and Seals or Sea-Carnivora, but all of these are air-breathers; even the Whale can only stay under water for a limited period of time. Hence we see that none of them are really animals belonging to the water; they are land animals adapted for life in the water.

This brings us very near to the last chapter in the Story of Animal Life. We have seen that our story began with the One-celled Animals, and went on with the tale of the Two-layered Animals, in which each layer was built up by cells in partnership. From Two-layered Animals we pa.s.sed to Three-layered Animals, and from them to Three-layered Animals with a "body-cavity." When we reached the latter, we found amongst them traces of the ancestry of the vertebrates. From the lowest of the Vertebrata, the Lancelet, we pa.s.sed on to the Lamprey, and from that to the true fishes. In the latter we found the parent type of all the other Vertebrata, possessing gills in the adult, while the latter only possess them, or traces of them, in early stages of growth. The Amphibia formed a group to themselves, in which we traced the loss of gills in the adult. In the Reptiles, four-legged egg-laying animals, we found not only a close relationship with birds, but also, through the four-legged egg-laying _Ornithorhyncus_, a relationship with the Mammalia. The last group comprises all the furry animals, and culminates in the order Primates, in which the great Cuvier included Man.

TABLE SHOWING THE DISTRIBUTION OF ANIMAL LIFE BETWEEN LAND AND WATER

KEY TO TABLE:

A ARTHROPODA.

B VERTEBRATA.

C CHORDATA.

LAND WATER

Except a few forms living --All the PROTOZOA.

living in damp places, or as parasites --All the SPONGES.

--All the COELENTERATA.

Except a few forms --VERMES.

terrestrial, and many parasitic

Insects, except --A very few adult forms and } Except Wood-lice and a few larvae. } a very few others --CRUSTACEA. } A Spider-like animals, } except --_Limulus._ } --All the BRACHIOPODA.

--All the POLYZOA.

--All the ECHINODERMATA.

Except the Land-snails --MOLLUSCA.

--HEMICHORDATA. } --UROCHORDATA, or Ascidians. } --All the Fishes: (some few can } exist in damp places) } } Amphibia belong to both. } } All the Reptiles --Except swimming forms, } } which are nevertheless } } air-breathers, only } } partially adapted for } } water life: Tortoises } } and Turtles, Crocodiles } } and Water-Snakes, _e.g._ } } C } } All the Birds: swimming and } B } diving forms are only adapted } } for temporary visits to the } } water } } All the Mammals --Except Whales, Sirenia, } } and Seals, which are } } nevertheless } } air-breathers, only } } partially adapted } } for water life. } }

Another volume of this series, "The Story of the Earth," has already dealt with the distribution of animal life in time; while "The Story of Animal Life in the Sea" tells about the present inhabitants of the ocean. It is therefore unnecessary to say much in this volume regarding the distribution of animal life. A table is, however, appended, which is not without interest. It shows how the chief great groups of animals are divided between land life and water life, whether in fresh water or salt. It will be seen that the terrestrial animals are much in a minority, and that they belong, for the most part, to the higher types.

They are, in fact, stragglers, bold emigrants from the early home of animal life, which lies in the more shallow parts of the waters of the sea.

CHAPTER XV

MAN

If we are to accept the opinion of Dr. Isaac Watts, man, as a moral being, is distinctly inferior to the "birds in their little nests," who live in harmony with one another; and, again, if we are to believe Solomon, he is by no means always the equal in intelligence of the Ant.

Yet somehow it came as a shock to many who had been accustomed to revere both these authors, when they were asked, early in the latter half of the nineteenth century, to regard man, from a zoological point of view, as just a little superior to the Apes.

Then arose a great agitation as to the possibility of finding the Missing Link. We shall see later on in this chapter, that if Research had been content, like Charity, to begin at home, its industry would have been duly rewarded.

But inquiry, carried far afield in time and place, has not been without result. For it is generally believed that the remains found in 1894 in Java by Dr. Eugene Dubois, are veritably those of the Missing Link.

These remains, which consist of the top of a skull, two teeth and a thigh bone, belong either to the oldest Pleistocene age, or to the upper Pliocene; they are found in a.s.sociation with the remains of other animals, among which are included some forms now extinct, or absent from that region. These ape-like remains have been carefully compared with those of the lowest races of man which have hitherto been found in a fossil state, and the result of the comparison is as follows: Of twelve experts present at the Zoological Congress held at Leyden, "three held that the fossil remains belonged to a low race of man, three declared them to be those of a man-like ape of great size; the rest maintained that they belonged to an intermediate form, which directly connected primitive man with the anthropoid apes" (Haeckel). To the creature represented by these bones has been a.s.signed the name of _Pithecanthropus erectus_, the Upright Ape-Man.

Let us now return from the subject of the Java fossil to those inquiries which, as we have above suggested, begin at home. We have already referred to the great principle of modern zoology, that the history of the development of the individual sums up the history of the development of the race. Of late years it has occurred to scientific men to apply this principle in the case of human beings, and to ask, "What can the baby teach us?"

The Baby, for one thing, has a very small nose, insignificant compared with the size of its jaw. At least scientists find that this is the case with their babies--if would, of course, be invidious to make such a remark regarding their friends' children; and still more so to add, that in this the Baby differs from the human adult, and somewhat resembles the Ape, in which the nose is still less prominent, and the jaw still more so. Observations have been made, too, regarding the Baby's remarkable power of "holding on" with its hands. While a Baby is, in most respects, a very weak creature, yet its powers of grip have been favourably compared with those of adult human beings. No one who has ever tried to rescue his watch or his hair from the clutches of a friend's Baby, will feel inclined to doubt the conclusions of scientific observers regarding the point in question.

The observations above referred to were made by Dr. Louis Robinson. He drew his conclusions from the study of sixty cases, all of them infants less than a month old; and of these at least half were tested within an hour of their birth.

In every instance except two, says Dr. Robinson, the child was able to hang on by its hands to the finger, or to a small stick three quarters of an inch in diameter, and to sustain the whole weight of its body for at least ten seconds. "In twelve cases, in infants under an hour old, half a minute pa.s.sed before the grasp relaxed, and in three or four cases nearly a minute." In infants of about four days old, increased strength was shown, and "nearly all, when tried at this age, could sustain their weight for half a minute. At about a fortnight or three weeks after birth the faculty appeared to have attained its maximum, for several at this period succeeded in hanging for over a minute and a half, two for over two minutes, and one infant of three weeks old for _two minutes thirty-five seconds_!" "Thus," says Dr. Robinson, "a three-weeks-old baby can perform a feat of muscular strength that would tax the powers of many a healthy adult. If any of my readers doubt this," he adds, "let them try hanging by their hands from a horizontal bar for three minutes."

In these facts Dr. Robinson finds something to remind us of the ape-babies that owe their safety to their capability of holding on to a tree-climbing mother; and also something to suggest connection with an ancestor which, although well accustomed to the use of its hands, had yet to learn the use of its feet for walking on flat ground.

The same author, in discussing the "Meaning of a Baby's Footprint," has shown that the foot of a young child bears traces of adaptation to a state of existence in which it was used for purposes other than that of walking.

"The toes of infants," says Dr. Robinson, "are much more mobile than those of adults. The great toe is shorter than the second and third, and is often separated from the second by a considerable interval.

The four outer toes can be, and frequently are, bent downwards so as to show a distinct knuckle on the upper aspect of the foot at the metatarso-phalangeal joint, and when at the same time the great toe is flexed and turned inwards towards the sole, the front part of the foot makes a very respectable fist. The great and little toes are often made to approach one another beneath the rest, and I have seen one child who could almost make them touch, and who habitually would endeavour to make the great toe oppose the others when any graspable object was brought into contact with the front part of the sole."[E]

[E] _Nineteenth Century_ for May, 1892.

Regarding the lines in the sole of the foot, Dr. Robinson says: "The sole is covered with lines of a character exactly similar to those on the hand; and when the toes are bent downwards these become deep creases, showing that they are, like the palmar lines, the natural folding-places of the integument to facilitate the action of grasping.... The lines are scarcely visible at fourteen months old, and are only present in a few cases after the age of two years. In adults no trace of them can be seen when the foot is at rest, and only the faintest indication at one or two spots when the toes are flexed to the utmost. The obliteration is doubtless owing to the foot being used as an organ for progression rather than prehension, and it will be seen that the most distinct line crosses the sole at the spot where the epidermis is always dense and callous, and the subcutaneous tissues thickened into a cushion-like pad by the pressure and friction consequent on walking.

This line undoubtedly marks the place where the chief fold in the skin was situated, when the toes were habitually clasped round some object such as the branch of a tree." It has been pointed out by other writers that the lines of the sole of the foot can plainly be seen in the adult foot of some savage races. It must be added, however, that the survival of the lines in the adult civilised foot is by no means so rare as Dr.

Robinson's remarks would lead one to suppose. I have seen instances in which they were quite clearly marked. It must be added that anyone who wishes to confirm my observations in this respect must be careful not to mistake lines of disfigurement, caused by the pressure of boots, which are sufficiently common, for the primitive lines of the foot.