Part 17

Eyes and noses are important keys to the bright colours of birds and comparative sombreness of hairy-coated creatures. Take a dog and an oriole as good examples of the two extremes. When a dog has lost his master, he first looks about; then he strains his eyes with the intense look of a near-sighted person, and after a few moments of this he usually yelps with disappointment, drops his nose to the ground, and with unfailing accuracy follows the track of his master. When the freshness of the trail tells him that he is near its end he again resorts to his eyes, and is soon near enough to recognise the face he seeks. A fox when running before a hound may double back, and make a close reconnaissance near his trail, sometimes passing in full view without the hound's seeing him or stopping in following out the full curve of the trail, so completely does the wonderful power of smell absorb the entire attention of the dog.

Let us now turn to the oriole. As we might infer, the nostrils incased in horn render the sense of smell of but slight account. It is hard to tell how much a bird can distinguish in this way--probably only the odour of food near at hand. However, when we examine the eye of our bird, we see a sense organ of a very high order. Bright, intelligent, full-circled, of great size compared to the bulk of the skull, protected by three complete eyelids; we realise that this must play an important part in the life of the bird. There are, of course, many exceptions to such a generalisation as this. For instance, many species of sparrows are dull-coloured. We must remember that the voice--the calls and songs of birds--is developed to a high degree, and in many instances renders bright colouring needless in attracting a mate or in locating a young bird.

As we have seen, the sense of smell is very highly developed among four-footed animals, but to make this efficient there must be something for it to act upon; and in this connection we find some interesting facts of which, outside of scientific books, little has been written. On the entire body, birds have only one gland--the oil gland above the base of the tail, which supplies an unctuous dressing for the feathers. Birds, therefore, have not the power of perspiring, but compensate for this by very rapid breathing. On the contrary, four-footed animals have glands on many portions of the body. Nature is seldom contented with the one primary function which an organ or tissue performs, but adjusts and adapts it to others in many ingenious ways. Hence, when an animal perspires, the pores of the skin allow the contained moisture to escape and moisten the surface of the body; but in addition to this, in many animals, collections of these pores in the shape of large glands secrete various odours which serve important uses. In the skunk such a gland is a practically perfect protection against attacks from his enemies. He never hurries and seems not to know what fear is--a single wave of his conspicuous danger signal is sufficient to clear his path.

In certain species of the rhinoceros there are large glands in the foot. These animals live among grass and herbage which they brush against as they walk, and thus "blaze" a plain trail for the mate or young to follow. There are few if any animals which care to face a rhinoceros, so the scent is incidentally useful to other creatures as a warning.

It is believed that the hard callosities on the legs of horses are the remains of glands which were once upon a time useful to their owners; and it is said that if a paring from one of these hard, horny structures be held to the nose of a horse, he will follow it about, hinting, perhaps, that in former days the scent from the gland was an instinctive guide which kept members of the herd together.

"Civet," which is obtained from the civet cat, and "musk," from the queer little hornless musk deer, are secretions of glands. It has been suggested that the defenceless musk deer escapes many of its enemies by the similarity of its secretion to the musky odour of crocodiles. In many animals which live together in herds, such as the antelope and deer, and which have neither bright colours nor far-reaching calls to aid straying members to regain the flock, there are large and active scent glands. The next time you see a live antelope in a zoological park, or even a stuffed specimen, look closely at the head, and between the eye and the nostril a large opening will be seen on each, side, which, in the living animal, closes now and then, a flap of skin shutting it tight.

Among pigs the fierce peccary is a very social animal, going in large packs; and on the back of each of these creatures is found a large gland from which a clear watery fluid is secreted. Dogs and wolves also have their odour-secreting glands on the back, and the "wolf-pack" is proverbial.

The gland of the elephant is on the temple, and secretes only when the animal is in a dangerous mood, a hint, therefore, of opposite significance to that of the herding animals, as this says, "Let me alone! stay away!" Certain low species of monkeys, the lemurs, have a remarkable bare patch on the forearm, which covers a gland serving some use.

If we marvel at the keenness of scent among animals, how incredible seems the similar sense in insects--similar in function, however different the medium of structure may be. Think of the scent from a female moth, so delicate that we cannot distinguish it, attracting a male of the same species from a distance of a mile or more. Entomologists sometimes confine a live female moth or other insect in a small wire cage and hang it outdoors in the evening, and in a short time reap a harvest of gay-winged suitors which often come in scores, instinctively following up the trail of the delicate, diffused odour. It is surely true that the greatest wonders are not always associated with mere bulk.

INSECT MUSIC

Among insects, sounds are produced in many ways, and for various reasons. A species of ant which makes its nest on the under side of leaves produces a noise by striking the leaf with its head in a series of spasmodic taps, and another ant is also very interesting as regards its sound-producing habit. "Individuals of this species are sometimes spread over a surface of two square yards, many out of sight of the others; yet the tapping is set up at the same moment, continued exactly the same space of time, and stopped at the same instant. After the lapse of a few seconds, all recommence simultaneously. The interval is always approximately of the same duration, and each ant does not beat synchronously with every other ant, but only like those in the same group, so the independent tappings play a sort of tune, each group alike in time, but the tapping of the whole mass beginning and ending at the same instant. This is doubtless a means of communication."

The organ of hearing in insects is still to be discovered in many forms, but in katydids it is situated on the middle of the fore-legs; in butterflies on the sides of the thorax, while the tip of the horns or antennæ of many insects is considered to be the seat of this function. In all it is little more than a cavity, over which a skin is stretched like a drum-head, which thus reacts to the vibration. This seems to be very often "tuned," as it were, to the sounds made by the particular species in which it is found. A cricket will at times be unaffected by any sound, however loud, while at the slightest "screek" or chirp of its own species, no matter how faint, it will start its own little tune in all excitement.

The songs of the cicadas are noted all over the world. Darwin heard them while anchored half a mile off the South American coast, and a giant species of that country is said to produce a noise as loud as the whistle of a locomotive. Only the males sing, the females being dumb, thus giving rise to the well-known Grecian couplet:

"Happy the cicadas' lives, For they all have voiceless wives."

Anyone who has entered a wood where thousands of the seventeen-year cicadas were hatching has never forgotten it. A threshing machine, or a gigantic frog chorus, is a fair comparison, and when a branch loaded with these insects is shaken, the sound rises to a shrill screech or scream. This noise is supposed--in fact is definitely known--to attract the female insect, and although there may be in it some tender notes which we fail to distinguish, yet let us hope that the absence of any highly organised auditory organ may result in reducing the effect of a steam-engine whistle to an agreeable whisper! It is thought that the vibrations are felt rather than heard, in the sense that we use the word "hear"; if one has ever had a cicada zizz in one's hand, the electrical shocks which seem to go up the arm help the belief in this idea. To many of us the song of the cicada--softened by distance--will ever be pleasant on account of its associations. When one attempts to picture a hot August day in a hay-field or along a dusty road, the drowsy zee-ing of this insect, growing louder and more accelerated and then as gradually dying away, is a focus for the mind's eye, around which the other details instantly group themselves.

The apparatus for producing this sound is one of the most complex in all the animal kingdom. In brief, it consists of two external doors, capable of being partly opened, and three internal membranes, to one of which is attached a vibrating muscle, which, put in motion, sets all the others vibrating in unison.

We attach a great deal of importance to the fact of being educated to the appreciation of the highest class of music. We applaud our Paderewski, and year after year are awed and delighted with wonderful operatic music, yet seldom is the limitation of human perception of musical sounds considered.

If we wish to appreciate the limits within which the human ear is capable of distinguishing sounds, we should sit down in a meadow, some hot midsummer day, and listen to the subdued running murmur of the myriads of insects. Many are very distinct to our ears and we have little trouble in tracing them to their source. Such are crickets and grasshoppers, which fiddle and rasp their roughened hind legs against their wings. Some butterflies have the power of making a sharp crackling sound by means of hooks on the wings. The katydid, so annoying to some in its persistent ditty, so full of reminiscences to others of us, is a large, green, fiddling grasshopper.

Another sound which is typical of summer is the hum of insects' wings, sometimes, as near a beehive, rising to a subdued roar. The higher, thinner song of the mosquito's wings is unfortunately familiar to us, and we must remember that the varying tone of the hum of each species may be of the greatest importance to it as a means of recognition. Many beetles have a projecting horn on the under side of the body which they can snap against another projection, and by this means call their lady-loves, literally "playing the bones" in their minstrel serenade.

Although we can readily distinguish the sounds which these insects produce, yet there are hundreds of small creatures, and even large ones, which are provided with organs of hearing, but whose language is too fine for our coarse perceptions. The vibrations--chirps, hums, and clicks--can be recorded on delicate instruments, but, just as there are shades and colours at both ends of the spectrum which our eyes cannot perceive, so there are tones running we know not how far beyond the scale limits which affect our ears. Some creatures utter noises so shrill, so sharp, that it pains our ears to listen to them, and these are probably on the borderland of our sound-world.

Pipe, little minstrels of the waning year, In gentle concert pipe! Pipe the warm noons; the mellow harvest near; The apples dropping ripe;

The sweet sad hush on Nature's gladness laid; The sounds through silence heard! Pipe tenderly the passing of the year. Harriet Mcewen Kimball.

I love to hear thine earnest voice, Wherever thou art hid, Thou testy little dogmatist, Thou pretty Katydid! Thou mindest me of gentlefolks,-- Old gentlefolks are they,-- Thou say'st an undisputed thing In such a solemn way. Oliver Wendell Holmes.

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AUGUST

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THE GRAY DAYS OF BIRDS

The temptation is great, if we love flowers, to pass over the seed time, when stalks are dried and leaves are shrivelled, no matter how beautiful may be the adaptation for scattering or preserving the seed or how wonderful the protective coats guarding against cold or wet. Or if insects attract us by their many varied interests, we are more enthusiastic over the glories of the full-winged image than the less conspicuous, though no less interesting, eggs and chrysalides hidden away in crevices throughout the long winter.