How different is the state of knowledge now, when every part of a crocodile or a cockroach is described in print in the minutest detail, and set before even the beginner in zoology as a necessary lesson.
But in spite of the labour necessary to master such detailed lessons, the study of the animal world is far from prosaic. The Story of Animal Life, indeed, bids fair to be the only element of romance left in the modern world for those who stay at home in their own land. The traveller of days of yore, when he ventured into the woods and fields, or upon the water, expected to meet with all sorts of strange things—fairies and elves and ugly gnomes; giants, ogres, and dragons; mermaids and water-witches. With the spread of education all these things have vanished now; it is quite certain that no Board-School-boy has ever met any of them: and one's walks abroad would be in these days as prosaic as they are safe, but for the world of animal life. If you have eyes for this, every field has its inhabitants, and every hedge its marvels. Instead of a fairy, you may be well contented to meet a dragon-fly with shining wings; instead of an ogre you will find the fierce spider, which not only makes away with every harmless fly that blunders into her net, but in many cases destroys her own kind also. Many a plant may be met with which has its own special caterpillar or other dependent insect, with ways of its own, which may amuse your idle hours. As for the change of a caterpillar or a tadpole into its adult form, it would be taken for a miracle if it were observed for the first time.
The reader may have noticed that there are some unfortunate people who have no eyes for these things; from childhood upwards they have been so absorbed in money-making or in reading books—the one case is as bad as the other—that they have never learnt to observe the facts of nature. Some cannot even recognise the different kinds of plants that they see in the hedges, or in a country walk. Such natures are intellectually defective; they are much to be pitied, and require a special training to remedy their stupidity. I mention this, because the occurrence of this form of stupidity is one of the dangers resulting from town life and bookish education, which we have to guard against at the present time.
But for all healthy people accustomed to the outdoor world, the study of animal life has always possessed an interest. Its interest has, however, been increased a hundred fold by the progress of modern discovery, which has taught us to see in the animal kingdom one large family, working its way upwards from humble beginnings, to more perfect structure of body, and more complete intelligence of mind.
CHAPTER II
HOW ANIMALS ADAPT THEMSELVES TO CIRCUMSTANCES
We all know what it is to adapt ourselves to circumstances. Suppose two lads, fresh from school, go out into the world to earn their living; one becomes a navvy and one a clerk. In five years' time these two young men will probably be very different in appearance from one another. The navvy will have developed his muscles; he will be broad-built, broad-chested, and strong. The clerk, on the other hand, will probably be comparatively weak and slim, his chest will not be so broad, his muscles will not be so well developed. The navvy, too, will probably be of a fresh complexion, while the clerk will be pale. All these differences are due to the fact that their bodies have adapted themselves to circumstances. Both men may be equally healthy, and equally long-lived. Let us take another example. Let us compare two other youths, of whom one becomes a cobbler and one an Alpine guide. The latter, in five years' time will have become a perfect specimen of muscular humanity—active, agile, and hardy. The cobbler will be comparatively stiff in his limbs and unable to undertake any singular feat of muscular exertion, although he may be able to do a very hard day's work at his own trade. The mountaineer, too, will probably differ in disposition from the cobbler. He will be daring, resourceful, and not afraid of danger under circumstances which would terrify the cobbler. Now let us suppose that the sons and grandsons of the navvy are brought up to be navvies, and the sons and grandsons of the clerk are brought up to be clerks;—that the children and grandchildren of the Alpine guide follow his own calling, and the children and grandchildren of the cobbler do the same;—we shall probably have four families differing very much in type of physique from one another. Yet take one of the navvy's sturdy grandchildren and bring him up as a clerk, and he will lose much of his sturdiness. Let the mountaineer's grandsons be brought up as cobblers, and by the time they are thirty they will not be remarkable for their muscular capabilities.
Just in a similar way the bodies of animals adapt themselves to circumstances. It is not always possible to trace the steps by which this has been done. But sometimes it is so; and we may find a whole series of varieties that are plainly due to adaptation. When we see an animal which is in some way especially fitted for its surroundings, we are therefore justified in concluding that it has become so by degrees.
The way in which animals adapt themselves to their surroundings in the matter of colour would afford material for several volumes each as large as this one. Those who have not travelled in foreign countries may perhaps find it difficult to realise that brilliant colouring and showy patterns can ever enable an animal to hide itself successfully. But an instance may be taken from an animal common on our own shores which will illustrate how this principle works.
In the spring there may be found in large numbers upon our rocky coasts a little oval shell-fish, about one-third of an inch long, sticking to the fronds of the tangle and other broad-leaved seaweeds. The animal is of a very pale brown colour; its shell brownish and semi-transparent, with several stripes of brilliant turquoise blue down the back. These stripes are not continuous, but interrupted at intervals so as to give them a beady look. Taken in the hand and looked at closely, the shell, with its contrast of blue stripes on a brown ground, is extremely conspicuous; brown being, in fact, the contrast-colour which shows blue in its greatest brilliancy. Yet, when perched upon the tangle, the creature is almost invisible, and might easily be mistaken for a natural irregularity of the surface of the seaweed. While the brown is the colour of the seaweed itself, the brilliant blue is indeed the exact colour of the spring sky at that season, everywhere reflected from the sea-water and from the wet surface of the seaweed. By matching that brilliant colour the animal therefore is rendered invisible. This little creature is the young of the Semi-transparent Limpet, Patella pellucida. This, at least, was the old-fashioned name for it, though it has received others. Its young and its adult form are so different in the appearance of the shell, that they have been described under different names. English readers who search for it in the spring will learn by experience that bright colouring may help to make a creature invisible. But this is not all that is to be said about the protective colouring of this little shell-fish. There are many creatures whose young live at the surface of the sea, and afterwards migrate to deeper water as they attain adult age. In early life they are transparent, because thus they best escape notice in the clear water of the surface, especially when seen from below, by the many enemies on the watch to devour them. But in their later life they become opaque, because thus they best escape notice from enemies watching from above, as they crawl along the bottom of the sea. Now this is the case with the little Patella. For this also migrates to the bottom—in this instance a comparatively short journey—when it is ready for adult life. Both shell and animal, therefore, are at first nearly transparent, but in older life both become more opaque; the blue stripes, too, are almost or quite obliterated in the after-growth of the shell, slight traces of them alone remaining at its apex. This change of colour fits the animal for the new home in which it settles, for it moves down from the leaf of the tangle to its root, and there finds a snug shelter among the coral-shaped branches of which the root is composed. Not many reflections of the blue sky are likely to reach the recesses of the tangle-root, so the creature has no longer any need of its protective colouring of blue.