Entomology
the branch of zoölogy jointed bodies and limbs, an enveloping cuticle of chitin, a ventral chain of ganglia, a dorsal brain, and breathe by airtubes or tracheæ. Contrasted with peripatus and myriopods, they have made two great steps of progress; the body is centralized, with locomotor limbs reduced to three pairs, and all the typical average forms have wings. Insects frequently have a metamorphosis in their life history. The adult body is divided into (1) a head, with three pairs of appendages (=legs), plus a pair of preoral outgrowths, the antennæ or feelers; (2) a thorax, with three pairs of jointed legs, typically plus two pairs of dorsal, compressed compressed sacs-the wings; (3) an abdomen, without legs, except in so far as these are rudimentarily represented in stings, ovipositors, etc. Insects exceed in number all other animals taken together. Over 80,000 species of beetles or coleoptera and about 15,000 moths and butterflies have been recorded; and Speyer estimates the total census at 200,000.
ENTOMOLOGY Form. The body of an insect consists of a distinct undivided head, probably a thorax with three divisions (pro, meso, and metathorax), and of an abdomen typically with 11 rings. antennæ, which are outgrowths of the head, not strictly comparable to legs, have often numerous nerve-endings and seem to be used in smelling, as organs of touch and guidance or in communicating impressions to friends. Exactly comparable with legs are the three pairs of mouth appendages, projecting downward or forward from the head, to which they are jointed and from which they are worked by muscles. The first pair, the mandibles (biting and chewing organs), more or less reduced in those insects A C B ENTOMOLOGY-SWALLOW-TAIL BUTTERFLY A. Larva C. Butterfly B. Pupa which suck, have but one joint and are without the lateral "palp" present in the crustacean organs of the same name.
Next come the first pair of maxillæ, which have jointed "palps." The second pair of maxillæ, are united at their base, and form the so-called labi labium, also prowhich have jointed "palps." The second pair of maxillæ, are united at their base, orders, and in association with the diverse diet, these three pairs of mouth organs vary vary greatly. orders, and in association with the dibears two pairs of dorsal outgrowths or verse diet, these three pairs of mouth thorax. They are undeveloped in some passive females and are likewise absent from many parasitic forms. In these cases the wings have been lost, while they have never been attained by the lowest insects. When at rest the wings cases the wings have been lost, while ENTOMOLOGY dragon flies and some others keep them expanded. The two pairs may be almost alike, as in bees and butterflies; those in front may be merely covers for flies. They are often hairy or scaly, the hind pair, as in beetles, or contorted (Strepsiptera); the hind pair may be linked to the fore pair, and are rudi- Locomotion.-Insects are emphatically locomotor animals. They walk, run and flies. They are often hairy or scaly, ally odoriferous. jump with the quadrupeds; they fly with locomotor animals. They walk, run and jump with the quadrupeds; they fly with and they swim with the fish. Even the the birds, they glide with the serpents; them along. The limbed larvæ, and especially the true caterpillars, often move them along. The limbed larvæ, and eswith great rapidity; a few jump, and pecially the true caterpillars, often move with great rapidity; a few jump, and many climb; others utilize their silken along by the forcible expulsion of water. young dragon flies propel themselves along by the forcible expulsion of water.
Skin. Insects have a firm chitinous cuticle formed from the epidermis or hybercles and hairs, of which the last are sometimes olfactory or otherwise senbercles and hairs, of which the last are ture there are often glands in connection sory. In spite of the ensheathing armawith the skin. Before the full size is reached there are often numerous skinwith the skin. Before the full size is reached there are often numerous skincastings or moltings. Sense-organs. - Except in fleas, lice, and the lowly Collembola, adult insects have compound eyes. These are often associated with simple eyes or ocelli, which are all that ever appear in larvæ, or fleas, and such insects. Blind insects also occur with other blind animals in the darkness of caves. Auditory organs are represented in almost all orders by peculiar nerve-endings superficially disthe tactile antennæ, and probably also on posed on various parts of the body. On the tactile antennæ, and probably also on the maxillary palps of various insects, there are specially innervated skin cells and hairs believed to be olfactory in function; while others more tion; while others more within the tiveness. The intelligence is greatest in and bees, where it is associated with the social insects-especially the ants complex though very small brains. within the complex though very small brains. canal always consists of fore-, mid-, and hind-gut. But the length and structure vary in different insects, to some extent in association with the differences of diet. The fore-gut includes mouth, phartent in association with the differences of diet. The fore-gut includes mouth, pharbe swollen into a crop, or bear an apynx, and gullet, of which the gullet may be swollen into a crop, or bear an ap- ENTOMOLOGY ach), or may be continued into a gizzard with hard grinding plates. The mid-gut is glandular, digestive, and absorptive; it often bears sacular outgrowths or glandular cæca, and has, as its origin implies, no chitinous lining.
The hind-gut is often coiled, terminally expanded in the rectum, and in that region sometimes associated with glands.
Respiratory System. Insects when resting often show panting movements in the abdomen, which is swayed by muscles whose activity is the chief condition of the circulation of air throughout the body. For in all insects the whole body is penetrated by air-tubes or tracheæ, which send fine branches into all the organs and tissues. These tubes are really ingrowths from the skin, and are lined by chitin, raised in what appear to be spiral thickenings which keep them elastically tense. In most cases these tracheæ open to the exterior by paired apertures or stigmata on the breast and abdomen, often guarded by hairs and very variously disposed. There are never more than 10 pairs of openings, though primitively there was probably a pair to each segment.
Many insects produce sounds which often express a variety of emotions. In some cases, when not simply automatic, these sounds serve the purpose of love songs; they may also express fear, ger, or even sorrow, or they may give alarm and convey tidings.
Circulatory System. - As the tissues are riddled with air-tubes, the need for definite blood-vessels is greatly lessened, and so the circulatory system is slightly developed in comparison with the thorough respiratory arrangements. The blood-which is colorless, yellow, greenish, or even reddish, with amœboid cells -flows for the most part along lacunæ without definite walls. The central organ is the dorsal blood-vessel or heart.
Metamorphosis. From the egg-shell of such insects as butterflies, beetles, flies, and bees, there emerges a larva (maggot, grub, or caterpillar) which lives a life of its own, growing, resting, and molting, often very active in its movements and voracious. Having accumulated a rich store of reserve food in its fat-body, the larva becomes for a longer time more or less quiescent, becomes a pupa, nymph, or chrysalis. In this stage, often within the shelter of a spun cocoon, great transformations occur: wings bud out, appendages of the adult pattern appear, reconstruction and centralization of organs are effected; and, finally, out of the pupal husk there emerges an imago or miniature fullyformed insect.
The Internal Metamorphosis. - In ENTOMOLOGY those forms which have no metamorphosis, or only an incomplete one, the organs of the larva develop continuously into those of the adult. It is otherwise in the complete metamorphosis of the higher insects. There the internal changes are as marked as the external; there is a gradual reconstruction of organs during the later larval, especially during the pupal stages. Most of the larval organs are absorbed by amœboid cells, and their débris is utilized in building up new structures.
General Life.- (a) While insects are predominantly active animals, we find in contrasting the families abundant illustration of the antithesis between activity and passivity. (b) In the majority of cases the adult insect is short-lived , and dies within a year; an adult Ephemerid may be literally the fly of a day, but from this there are many graduations leading up to the rare cases of a queenbee five years old, or an aged queen ant of thirteen. (c) Reproduction in a great number of insects of both sexes is shortly followed by death, love being in such cases at once the climax and end of life.
Economic Import.-As far as insects are concerned, the struggle between man and animals is by no means finished.
Direct injuries to man's person are familiarly illustrated in the parasitism fleas, lice, and other more or less intimate "boarders"; but these are less important than the share the mosquito Elephantiasis arabum. Personal injuries seems to have in the loathsome disease are dwarfed when we think of those done to property, and especially to crops and herds, by voracious or by parasitic insects. Clothes-moth and furnitureborer, vine-insects and Colorado beetle, the botflies which attack sheep, cattle, and horses are familiar illustrations of formidable pests. It should also be noted how the hostile insects which infest forest trees and vegetation generally may occasion changes which have far-off effects on the fauna, scenery, and even climate of a countryside. The majority of plants are dependent on insects, as the unconscious bearers of the pollen essential to the normal cross-fertilization of flowers.
Plants and Insects. - Many insects injure plants without any compensating benefit, and in this connection there are numerous cases in which plants and insects (especially ants) form a mutual partnership. Such plants are saved by their bodyguard of ants from unwelcome visitors, and the benefit is sometimes returned by the growth of special shelters, tenanted by the partner-insects.
ENTRE DOURO E MINHO ENTRE DOURO E MINHO (en'tre dō'rö ā mēn'yö), or MINHO, a province of Portugal, in the extreme N. W. of the country, bounded on the N. by the Minho river, and on the S. by the Douro river.
It has been called the Paradise of Portugal. The climate is agreeable and healthy. The chief productions are wine, oil, flax, maize, wheat, barley, oats, and vegetables. Wine is shipped largely at Oporto, the capital. Along the coast are numerous fisheries, at which great numbers find employment. The province of Minho consists of three districts, Braga, Vianna, and Oporto. Pop. about 1,300,000.
ENTRE RIOS (en'trā rē'ōs) ("between rivers"), a province of the Argentine Republic, between the Paraná and the Uruguay rivers. Estimated area, 29,021 square miles: pop. about 430,000.
The country is chiefly pastoral, but an increasing proportion is being put under cultivation, about 300,000 acres being now devoted to maize and wheat. The province is fertile, and well watered, being subject, in the S., to annual floods; nevertheless, the climate is very healthy.
Lime and gypsum are worked. The province has about 500 miles of railway. The capital is Paraná.