Sense of Sight.— The compound or 'facetted eyes (=mates) are composed of numerous simple eyes called ommanclia, which vary in number from 12, in Lepisma, to 20,000 in the n-fly (ischna), and even 25,000 in e (illordello). Yet notwithstanding the wonderful complexity of these compound eyes, mbst insects are near-sighted, and perceive rather the movements of other animals than their exact outlines; the dragonfly and butter. fly can see for a considerable distance. The simple eye probably only enables the insect to distinguish daylight from darkness, or at most very near objects. Insects, like bees and butter. flies, have the color-sense, and prefer certain colors to others.
Sense of Smell.-- Insects are chiefly guided by the sense of smell. This reeides in the an tenna, in which there are microscopic pits filled with fluid; to this pit goes a fine nerve whose fibres end in staff-like sense cells. The number' of these olfactory organs is in some insects enormous; thus in the European cockchafer there are 39,000 in the leaves of the male anten4 nm, and about 35,000 in those of the female; in a single antenna of the hornet (Vespa crabro) are about 13,000 to 14,000. In the cock., roach the abdominal cerci or feelers also pos. sess such pits.
Sense of Hearing.— The auditory organs of the locust are drum-like ears situated one 'on each side of the base of the abdomen, directly behind the first abdominal spiracle; in the green grasshopper, katydids, etc., a little auditory sac is lodged in the fore-legs (tibia). It is awl posed that most insects are destitute of the sense of hearing, at least auditory structures have not yet been detected; yet all sound-pro ducing insects must have ears to hear.
Sense of Taste.— The ' taste org.ans are little pits or papilla: which resemble the olfac tory organs, but which occur on the inside of the upper lips, on the epipharynx, or at the base of the proboscis and maxillae in the bee.
The Egg and Growth of Insects.— The eggs and the fertilizing fluid of the male are produced in glands which open near the end of the body on the under side. The eggs are de posited •by the female in the earth or in wood, leaves, etc., by means of the ovipositor, an apparatus composed of three pairs of hard ap pendages, and which in the wasps and bees form the sting. Most insects die on the ap proach of •cold weather, when they lay their eggs, the species being represented in the win ter by the eggs alone. The eggs hatch in spring, the embryo passing through remarkable changes.
Metamorphoses.— Most insects after hatch ing pass through a remarkable series of changes called a metamorphosis. The small flies, moths or beetles are not the young of large ones, but adult insects, while the most primitive insects have no marked metamorphosis, the mature locust only differing from the young in having wings.; the more specialized forms as beetles, moths, wasps, bees and flies, pass through two stages of growth, that is, the larva and pupa, before becoming winged and sexually mature.
Larva.—The name was first given by the ancients to the caterpillar because they thought it masked the form of the perfect insect. Swam merdam supposed that the larva contained within itself the germ of the future butterfly, enclosed in what will be the case of the pupa, which is itself included in three or more skins, one over the other, that will successively cover the larva?' But the discovery by Wcismann (q.v.) of the germs of the imago (imaginal discs or buds) in the larva completely changed our notions of the nature of metamorphosis (q.v.), and revolutionized our knowledge of the
fundamental processes concerned in the change from larva to pupa or chrysalis, and from pupa to imago. Not only are the larvae,of each order of insects characteristic in form, so that the grub or larva of beetles is readily distinguished from the larva of other groups, or the maggots of flies from the footless larva of ants, wasps and bees, but within the limits of the larger Orders there is a great diversity of larval forms, showing that they are the result of adaptation to their surroundings and mode of life.
The larva of nearly if not all the meta bolous animals are probably secondary in their origin. Fritz Muller (q.v.) pointed out that this is the case with the larva of the higher insects. The larva of a beetle is popularly called a grub; that of a fly a maggot. The young of the more primitive insects, such as the cockroach, locust, all bugs, etc., which un dergo an incomplete metamorphosis, is called a nymph. See LARVA.
The word pupa is Latin, meaning baby. Linnaeus gave it this name from its resemblance to a baby which has•been swathed or bound up, as is still the custom in southern Europe. The term pupa should be restricted to the resting, inactive stage of the holometabolous insects, that is, those with a complete metamor phosis. The typical pupa is that of a moth or a butterfly, popularly called 'a chrysalis. A lepi dopterous oupa in which the appendages are more or less folded 'close to the body and sold ered to the integument, was called by Linitaus a pupa obtecta; and when the limbs are free, as in Neuroptera, Mecoptera, Trichoptera, and the lepidopterous genus Micropteryx, it is called a pupa libera. When the pupa is enclosed in the old larval skin, which forms a pupal covering (puparium), the pupa was said by Linnaeus to he coarctate. The pupa of certain 'Diptera, as that of the orthoraphous families, is nearly as much obtected as that of the tineoid families of moths, especially as regards the appendages of the head, the legs being more as in pupie libera The pupa of Coleoptera and of Hymenoptera, though there is, apparently, no near, relationship between these two orders, are much alike in shape, and, as Chapman pertinently suggests, those of both orders are helpless from their quiescence, and hence have resorted for pro tection to some cocoon or shell. But it is quite otherwise with the pupa of Lepidoptera and Diptera, which vary so muds in adaptation to their surroundings, and hence afford important taxonomical and p&ylogenetic characters. This, as regards the Lepidoptera, was almost wholly overlooked until Chapman called attention to the subject, and showed that the pupa had characters of their own, of the greatest service in working out the classification, and hence the phylogeny of the different lepidopterous groups. The pupa of the Neuroptera, Coleop tera and Hymenoptera differ structurally from the imago, in the parts of the head and thorax being less differentiated. Thus in the head the limits of sutures between the epicranium and clypeus, and the occiput and gula, are obscurely marked, while the tergal and pleural sclerites of the imago are not well differentiated until the changes occurring just before the final ecdysis. It is easy, however, to homologize the appen dages of the pupa with those of the imago of all the holometabolous orders except in the case of the obtected pupa of the Lepidoptera (and probably of the obtected dipterous pupa), where the cephalic appendages are soldered together.