In the Cyclorrhapha on the other hand, in which the actual pupa is concealed within the hardened larval skin, the imago escapes through a circular orifice formed by pushing off or through the head end of the puparium.
Of the head-capsule in the imago, it appears that the clypeus and FIG.
On the other hand, we find in the vast majority of the Hexapoda a very marked difference between the perfect insect (imago) and the young animal when newly hatched and for some time after hatching.
I., II., III., vomitories) the imaginal disks are to all the three thoracic segments appearance completely separated from of the larva; I, 2, 3, buds the hypodermis, with which they are, of the legs of the imago; la, however, really organically connected bud of head-lobes; f, of by strings or pedicels.
The mature dragon-fly nymph, for example, makes its way out of the water in which the early stages have been passed and, clinging to some water-plant, undergoes the final ecdysis that the imago may emerge into the air.
After a prolonged aquatic larval and nymphal life-history, the winged insect appears as a sub-imago, whence, after the casting of a delicate cuticle, the true imago emerges.
If we admit that the larva has, in the phylogeny of insects, gradually diverged from the imago, and if we recollect that in the ontogeny the larva has always to become the imago (and of course still does so) notwithstanding the increased difficulty of the transformation, we cannot but recognize that a period of helplessness in which the transformation may take place is to be expected.
Moreover, in many insects with imperfect metamorphosis the change from larva or (as the later stage of the larva is called in these cases) nymph to imago is about as great as the corresponding change in the Holometabola, as the student will recognize if he recalls the histories of Ephemeridae, Odonata and male Coccidae.
A common result of metamorphosis is that the larva and imago differ markedly in their habitat and mode of feeding.
The larva may be aquatic, or subterranean, or a burrower in wood, while the imago is aerial.
It may bite and devour solid food, while the imago sucks liquids.
It may eat roots or refuse, while the imago lives on leaves and flowers.
A marked disproportion between the life-term of larva and imago is common; the former often lives for months or years, while the latter only survives for weeks or days or hours.
Mandibles present in pupa, vestigial in imago; maxillae suctorial without specialization; first maxillae with lacinia, galea and palp. Prothorax small.
Mandibles absent in imago, very exceptionally present in pupa; first maxillae nearly always without laciniae and often without palps, or only with vestigial palps, their galeae elongated and grooved inwardly so as to form a sucking trunk.
Fragmentary as the records are, they show that the Exopterygota preceded the Endopterygota in the evolution of the class, and that among the Endopterygota those orders in which the greatest difference exists between imago and larva - the Lepidoptera, Diptera and Hymenoptera - were the latest to take their rise.
The sub-imago of the Ephemeroptera suggests that a moult, after the wings had become functional, was at one time general among the Hexapoda, and that the resting nymph of the Thysanoptera or the pupa of the Endopterygota represents a formerly active stage in the life-history.
For in the post-embryonic development of the ancestors of the Endopterygota we may imagine two or three instars with wing-rudiments to have existed, the last represented by the sub-imago of the may-flies.
As the life-conditions and feedinghabits of the larva and imago become constantly more divergent, the appearance of the wing-rudiments would be postponed to the pre-imaginal instar, and that instar would become predominantly passive.
As shown by the number and variety of species, the Orthoptera are the most dominant order of this group. Eminently terrestrial in habit, the differentiation of their fore-wings and hindwings can be traced from Carboniferous, isopteroid ancestors through intermediate Mesozoic forms. The Plecoptera resemble the Ephemeroptera and Odonata in the aquatic habits of their larvae, and by the occasional presence of tufted thoracic gills in the imago exhibit an aquatic character unknown in any other winged insects.
The Neuroptera, with their similar foreand hind-wings and their campodeiform larvae, seem to stand nearest to the presumed isopteroid ancestry, but the imago and larva are often specialized.
And thus perfection of structure and instinct in the imago has been accompanied by degradation in the larva, and by an increase in the extent of transformation and in the degree of reconstruction before and during the pupal stage.
That on geography is particularly good, and is interesting as having been read by Columbus, who lighted on it in Petrus de Alliaco's Imago Mundi, and was strongly influenced by its reasoning.
His fundamental physical maxims are matter and force; the latter he calls virtus, species, imago agentis, and by numberless other names.
The head is rather large, and is furnished at first with five simple eyes of nearly equal size; but as it increases in size the homologues of the facetted eyes of the imago become larger, whereas those equivalent to the ocelli remain small.
But this is not yet perfect, although it has all the form of a perfect insect and is capable of flight; it is what is variously termed a "pseudimago," "sub-imago" or "pro-imago."
The transformations from the larval state are completed within the gall, out of which the imago, or perfect insect, tunnels its way, - usually in autumn, though sometimes, as has been observed of some individuals of Cynips Kollari, after hibernation.
(Rome, 1601-1602, both contemporaries of Paul III.); Quirini, Imago optimi.
The size of the imago on the focal plane is always equal to its actual size, and is independent of the distance of the object from the plane focused for.
Cervin, Imago virtutum Roberti card.
The insect, which may have become an imago with the Gordian larva still in it, is then eaten by a carnivorous insect or by a fish, and the contained Gordian larva becomes elongate and mature in its second host.
Imago, perhaps from the same root as imitari, copy, imitate), in general, a copy, representation, exact counterpart of something else.
Thus the reflection of a person in a mirror is known as his "image"; in popular usage one person is similarly described as "the very image" of another; so in entomology the term is applied in its Latin form imago to an insect which, having passed through its larval stages, has achieved its full typical development.
They are abundantly distinct from the Neuroptera and Mecaptera, through the absence of mandibles in the imago, the maxillae - both pairs of which possess the typical inner and outer lobes and jointed palps - forming a suctorial apparatus.
Reference has been made above to the possibility that the Roman imago of an ancestor actually embodied his ghost, at least on solemn occasions.
They are as follows: Institutum Societatis Jesu (7 vols., Avignon, 1830-1838); Orlandini, Historia Societatis Jesu (Antwerp, 1620); Imago primi saeculi Societatis Jesu (Antwerp, 1640); Nieremberg, Vida de San Ignacio de Loyola (9 vols., fol., Madrid, 1645-1736); Genelli, Life of St Ignatius of Loyola (London, 1872); Backer, Bibliotheque des ecrivains de la Compagnie de Jesus (7 vols., Paris, 1853-1861); Cretineau Joly, Histoire de la Compagnie de Jesus (6 vols., Paris, 1844); Guettee, Histoire des Jesuites (3 vols., Paris, 1858-1859); Wolff, Allgemeine Geschichte der Jesuiten (4 vols., Zurich, 1789-1792); Gioberti, Il Gesuita moderno (Lausanne, 1846); F.