sessor.

the shell as exactly as the lid or operculum of its original posIt is surprising how rapidly they will run about with the dwelling they have appropriated on their back; and when by the progress of their growth it becomes uncomfortably narrow, the remedy is easy, as convenient shells abound wherever hermit-crabs exist.

Thus we find a wonderful harmony between the organization of the paguri and the structure of the alien domicile to which they owe their safety, and which serves to complete their existence. Evidently the same creative idea has given birth to the mollusc and the crab, for how could mere fortuitous circumstances have produced so marvellous a relation between animals belonging to two classes so widely distinct?

In point of intelligence the crustaceans are far inferior to the insects. Their instincts are confined to the violent seizure or the cunning entrapping of their prey, to the burrowing of a hole in the ground, or to the seeking of a shell fit for the concealment of their otherwise defenceless body: in them we find no care for their young, no mutual affection, no joint labours for the welfare of a large community, no love—but frequent outbursts of an angry and quarrelsome temper.

The land-crabs, however, afford us a remarkable instance of that wonderful migratory instinct which in the following chapters we shall have frequent occasion to admire. These animals generally spend their days in holes and cavities among the mountains; but when the season for spawning arrives, vast armies of them set out from the hills, marching in a direct line towards the sea-shore, for the purpose of depositing their eggs, which are attached to the lower surface of the abdomen and are washed off by the surf. On this grand expedition they pursue so direct a line to the place of their destination that scarcely anything will divert their course; even the most formidable obstacles are overcome by their unyielding perseverance. When they have effected the purpose for which they undertook their journey, they recommence their toilsome march to their upland retreats. They set out after nightfall, and steadily advance until the approach of daylight warns them to seek concealment in the inequalities of the ground, or among any kind of rubbish, where they lie ensconced until the stars again invite them to pursue their undeviating course. Of the

thousands that originally left the damp forest-grounds, comparatively but a small number return, emaciated and exhausted, to their mountain-burrows, and a few weeks after, millions of the little crabs which have been hatched on the shore may be seen making their way up to the hills. Who can explain to us the mysterious voice which prompts them to seek an unknown home, so different from the scene where they first drew breath; who tells them that far from the torrid shore they are sure to find a more congenial retreat in the cool shades of the forest; and who, throughout countless years, directs these constant migrations from the sea to the uplands, and then again from the mountains to the brink of the ocean?

CHAPTER XXII.

INSECTS.

Their Integuments-Their Metamorphoses--Larva-Pupa-Perfect Insects— Antennæ-Eyes-Masticatory Organs-Chewing and Sucking Insects-Digestive Organs of the Carnivorous and Herbivorous Insects-Motions of InsectsElateride-Aquatic Insects-Foot of the Fly-Wings-Respiratory Organs— Trachea and Stigmata-The Butterfly's Wing under the Microscope-Defences of Insects-Vitality-Concealments-The Caddice Fly-The Small Ermine Moth -The Clothes Moth-Hunting Manœuvres of the Mantis-The Ant Lion—The Larva of the Tiger Beetle-Insect Plagues-Insects Useful to Man-Their Numberless Enemies-Their Wonderful Instincts-Care for their Young-The Rhynchites Betula - Dung and Sexton Beetles-Their Remarkable Intelligence The Sand Wasp-Ichneumon Flies-Breeze Flies-The Earwig-The Mole Cricket-The Dirt Dauber and Trypoxylon-The Leaf Cutters-The Carpenter Bee-The Chartergus Nidulans-The Hive Bee-The Ants and Termites.

THOUGH small in size, the Insects are great, by their infinite varieties of form, their prodigious numbers, their wonderful organization, their astonishing metamorphoses, and their truly marvellous instincts. From whatever point of view we may consider them, they constantly afford new subjects of admiration and delight; for all that is either beautiful and graceful, interesting and alluring, or curious and singular in every other class and order of the animal world has been combined and concentrated in these miniature masterpieces of Nature, a glimpse into whose economy opens to every reflective mind the portals of the spiritual world, and plainly reveals the Deity who called them into life.

A thick and weighty harness of chalk, like that of the crustaceans, would have been far too cumbersome for delicate and tiny creatures, generally destined for rapid motions; and thus we find the insects covered with a thin vestment of incorruptible chitine, a hornlike substance equally light and strong, which, without considerably adding to their weight, answers every

purpose of protection, and, shaped into myriads of graceful forms, frequently glows with the most vivid colours. A robe more beautiful and appropriate than this cannot possibly be imagined.

A closer examination of the insect-skeleton shows us that it consists of a number of rings or segments, either distinct or soldered together, and forming three principal parts—the head, the breast or thorax, and the abdomen. The head, which has generally the form of a hollow globe, is the product of at least three segments moulded into one, and contains the organs of mastication, the antennæ, and the eyes; the thorax invariably consists of three rings or segments, and bears the single or double pair of wings which most of the perfect insects possess, as well as the three pair of feet with which all of them are furnished; the abdomen, finally, is formed of a larger number of distinct segments, freely moveable one above the other.

Such is the ground-plan according to which the skeleton of all insects is constructed, but their forms are varied to answer an infinite variety of wants: for the insects gnaw and devour all organic substances without exception; they feed upon the whole vegetable kingdom, from the palm to the lichen, and from the hardest root to the most delicate blossom. They are not only at perpetual feud among themselves, but engaged in constant war with the higher animals; they inhabit every climate; they select every conceivable dwelling-place, from the caverns of the subterranean world to the pinnacles of the Alps; and thus we can conceive the endless varieties of structure, of instruments, and weapons which the immense range of their existence naturally requires.

More than one hundred thousand different species of insects have already been described by entomologists, and each of them is distinguished from its nearest relations by some modification of structure best adapted to its peculiar sphere of life. The most retentive memory would be utterly unable to embrace this amazing variety of forms; and yet a vast number of insects is still utterly unknown, and their countless legions constitute but a part of the animated beings that people our little earth -itself but a speck in the boundless universe! How wondrous are the works of the Creator-how beyond all human conception His wisdom and His power!

METAMORPHOSES OF INSECTS.

191

The immense gallery of insect life swells into still grander proportions when we reflect that each insect passes through several metamorphoses or stages of development before it assumes its perfect form, exhibiting as it were several distinct beings during the course of its existence. At first it issues from the egg either as a head-and-footless maggot (a), or provided with a head and six thoracic legs like a true larva (b), or possessing a still larger number of feet like a caterpillar (c). A boundless appetite, an insatiable voracity characterise this first juvenile age of insect life. Thus, to mention but one instance, the silkworm, which at its birth weighs but the hundredth part of a grain, devours in thirty days more than an ounce of leaves, sixty thousand times more than its original weight! According to this mea

sure a child, which when born weighs about ten pounds, would consume during the same period no less than 6,000 hundredweight of food, to the amazement and terror of its parents. No wonder that so vast a supply of aliment produces a rapid growth, and that during the thirty days of her existence the silkworm larva increases 9,500 times in weight; no wonder also that she soon feels her dress too narrow, and more than once sheds her skin to provide room for the swelling proportions of her body! But now a period of inactivity succeeds, and, generally after the fifth shedding of her skin, a great change takes place in the