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Insects as a whole are preeminently creatures of the land and the air. This is shown not only by the possession of wings by a vast majority of the class, but by the mode of breathing to which reference has already been made (p. 2), a system of branching air-tubes carrying atmospheric air with its combustion-supporting oxygen to all the insect's tissues. The air gains access to these tubes through a number of paired air-holes or spiracles, arranged segmentally in series.

It is of great interest to find that, nevertheless, a number of insects spend much of their time under water. This is true of not a few in the perfect winged state, as for example aquatic beetles and water-bugs ('boatmen' and 'scorpions') which have some way of protecting their spiracles when submerged, and, possessing usually the power of flight, can pass on occasion from pond or stream to upper air. .....

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Publié par	eBookIt.com
Date de parution	25 mars 2013
Nombre de lectures	1
EAN13	9781456614805
Langue	English

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Extrait

THE LIFE-STORY OF INSECTS

by George H. Carpenter

Digital edition produced & published by Sai ePublications www.saiepublications.com
Frontispiece . Transformation of a Gnat ( Culex ). Magnified 5 times. Larva. (The head is directed downwards and the tail-siphon with spiracle points upwards to the surface of the water.) Pupal Cuticle from which the Imago is emerging. (The pair of 'respiratory trumpets' on the thorax of the pupa are conspicuous. The wings of the Imago are crumpled, and the hind feet are not yet withdrawn.) Adult Gnat. Female.
PREFACE
The object of this little book is to afford an outline sketch of the facts and meaning of insect-transformations. Considerations of space forbid anything like an exhaustive treatment of so vast a subject, and some aspects of the question, the physiological for example, are almost neglected. Other books already published in this series, such as Dr Gordon Hewitt's House-flies and Mr O H. Latter's Bees and Wasps , may be consulted with advantage for details of special insect life-stories. Recent researches have emphasised the practical importance to human society of entomological study, and insects will always be a source of delight to the lover of nature. This humble volume will best serve its object if its reading should lead fresh observers to the brookside and the woodland.
G. H. C.
Dublin, July , 1913.
TABLE OF CONTENTS
Cover Image
Title Page
Chapter 1: Introduction
Chapter 2: Growth and Change
Chapter 3: The Life-stories of some Sucking Insects
Chapter 4: From Water to Air
Chapter 5: Transformations, Outward and Inward
Chapter 6: Larvae and their Adaptations
Chapter 7: Pupae and their Modifications
Chapter 8: The Life-story and the Seasons
Chapter 9: Past and Present—the Meaning of the Story
LIST OF ILLUSTRATIONS Stages in the Transformations of a Gnat Frontispiece Stages of the Diamond-back Moth ( Plutella cruciferarum ) Head of typical Moth Head of Caterpillar Common Cockroach ( Blatta orientalis ) Nymph of Locust ( Schistocera americana ) Aphis pomi , winged and wingless females Mussel Scale-Insect ( Mytilaspis pomorum ) Emergence of Dragon-fly ( Aeschna cyanea ) Nymph of May-fly ( Chloeon dipterum ) Imaginal buds of Butterfly Imaginal buds of Blow-fly Carrion Beetle ( Silpha ) and larva Larva of Ground-beetle ( Aepus ) Willow-beetle ( Phyllodecta ) and larva Cabbage-beetle ( Psylliodes ) and larva Corn Weevil ( Calandra ) and larva Ruby Tiger Moth ( Phragmatobia fuliginosa ) Larvae and Pupa of Hive-bee ( Apis mellifica ) Larva of Gall-midge ( Contarinia nasturtii ) Crane-fly ( Tipula oleracea ) and larva Maggot of House-fly ( Musca domestica ) Ox Warble-fly ( Hypoderma bovis ) with egg, larva, and puparium Pupa of White Butterfly ( Pieris )
CHAPTER I: INTRODUCTION
Among the manifold operations of living creatures few have more strongly impressed the casual observer or more deeply interested the thoughtful student than the transformations of insects. The schoolboy watches the tiny green caterpillars hatched from eggs laid on a cabbage leaf by the common white butterfly, or maybe rears successfully a batch of silkworms through the changes and chances of their lives, while the naturalist questions yet again the 'how' and 'why' of these common though wondrous life-stories, as he seeks to trace their course more fully than his predecessors knew.

Fig. 1. a , Diamond-back Moth ( Plutella cruciferarum ); b , young caterpillar, dorsal view; c , full-grown caterpillar, dorsal view; d , side view; e , pupa, ventral view. Magnified 6 times. From Journ. Dept. Agric. Ireland , vol. I.
Everyone is familiar with the main facts of such a life-story as that of a moth or butterfly. The form of the adult insect (fig. 1 a ) is dominated by the wings—two pairs of scaly wings, carried respectively on the middle and hindmost of the three segments that make up the thorax or central region of the insect's body. Each of these three segments carries a pair of legs. In front of the thorax is the head on which the pair of long jointed feelers and the pair of large, sub-globular, compound eyes are the most prominent features. Below the head, however, may be seen, now coiled up like a watch-spring, now stretched out to draw the nectar from some scented blossom, the butterfly's sucking trunk or proboscis, situated between a pair of short hairy limbs or palps (fig. 2). These palps belong to the appendages of the hindmost segment of the head, appendages which in insects are modified to form a hind-lip or labium , bounding the mouth cavity below or behind. The proboscis is made up of the pair of jaw-appendages in front of the labium, the maxillae , as they are called. Behind the thorax is situated the abdomen, made up of nine or ten recognisable segments, none of which carry limbs comparable to the walking legs, or to the jaws which are the modified limbs of the head-segments. The whole cuticle or outer covering of the body, formed (as is usual in the group of animals to which insects belong) of a horny (chitinous) secretion of the skin, is firm and hard, and densely covered with hairy or scaly outgrowths. Along the sides of the insect are a series of paired openings or spiracles, leading to a set of air-tubes which ramify throughout the body and carry oxygen directly to the tissues.

Fig. 2. A. Head of a typical Moth, showing proboscis formed by flexible maxillae ( g ) between the labial palps ( p ); c , face; e , eye; the structure m has been regarded as the vestige of a mandible. B. Basal part ( b ) of maxilla removed from head, with vestigial palp ( p ). Magnified.
Such a butterfly as we have briefly sketched lays an egg on the leaf of some suitable food-plant, and there is hatched from it the well-known crawling larva[1] (fig. 1 b, c, d ) called a caterpillar, offering in many superficial features a marked contrast to its parent. Except on the head, whose surface is hard and firm, the caterpillar's cuticle is as a rule thin and flexible, though it may carry a protective armature of closely set hairs, or strong sharp spines. The feelers (fig. 3 At ) are very short and the eyes are small and simple. In connection with the mouth, there are present in front of the maxillae a pair of mandibles (fig. 3 Mn ), strong jaws, adapted for biting solid food, which are absent from the adult butterfly, though well developed in cockroaches, dragon-flies, beetles, and many other insects. The three pairs of legs on the segments of the thorax are relatively short, and as many as five segments of the abdomen may carry short cylindrical limbs or pro-legs, which assist the clinging habits and worm-like locomotion of the caterpillar. No trace of wings is visible externally. The caterpillar, therefore, differs markedly from its parent in its outward structure, in its mode of progression, and in its manner of feeding; for while the butterfly sucks nectar or other liquid food, the caterpillar bites up and devours solid vegetable substances, such as the leaves of herbs or trees. It is well-known that between the close of its larval life and its attainment of perfection as a butterfly, the insect spends a period as a pupa (fig. 1 e ) unable to move from place to place, and taking no food.
[1] The term larva is applied to any young animal which differs markedly from its parent.

Fig. 3. Head of Caterpillar of Goat-moth ( Cossus ) seen from behind. At , feeler; Mn , mandible; Mx , maxilla; Lm , labium, spinneret projecting beyond it. Magnified. After Lyonet from Miall and Denny's Cockroach .
Such, in brief, is the course of the most familiar of insect life-stories. For the student of the animal world as a whole, this familiar transformation raises some startling problems, which have been suggestively treated by F. Brauer (1869), L. C. Miall (1895), J. Lubbock (1874), R. Heymons (1907), P. Deegener (1909) and other writers[2]. To appreciate these problems is the first step towards learning the true meaning of the transformation.
[2] The dates in brackets after authors' names will facilitate reference to the Bibliography (pp. 124-8).
The butterfly's egg is absolutely and relatively of large size, and contains a considerable amount of yolk. As a rule we find that young animals hatched from such eggs resemble their parents rather closely and pass through no marked changes during their lives. A chicken, a crocodile, a dogfish, a cuttlefish, and a spider afford well-known examples of this rule. Land-animals, generally, produce young which are miniature copies of themselves, for example horses, dogs, and other mammals, snails and slugs, scorpions and earthworms. On the other hand, metamorphosis among animals is associated with eggs of small size, with aquatic habit, and with relatively low zoological rank. The young of a starfish, for example, has hardly a character in common with its parent, while a marine segmented worm and an oyster, unlike enough when adult, develop from closely similar larval forms. If we take a class of animals, the Crustacea, nearly allied to insects, we find that its more lowly members, such as 'water-fleas' and barnacles, pass through far more striking changes than its higher groups, such as lobsters and woodlice. But among the Insects, a class of predominantly terrestrial and aerial creatures producing large eggs, the highest groups undergo, as we shall see, the most profound changes. The life-story of the butterfly, then, well-known as it may be, furnishes a puzzling exception to some wide-reaching generalisations concerning animal development. And the student of science often finds that an exception to some rule is the key to a problem of the highest interest.
During many centuries naturalists have bent their energies to explain the difficulties presented by insect transformations. Aristotle, the first serious student of organised beings whose writings have been preserved for us, and William Harvey, the famous demonstrator of the mammalian blood