The Structure And Life-History Of The Cockroach (Periplaneta Orientalis) - free ebook by Alfred Denny

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The Structure And Life-History Of The Cockroach (Periplaneta Orientalis)

Alfred Denny

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THE STRUCTURE AND LIFE-HISTORY OF THE COCKROACH (PERIPLANETA ORIENTALIS) An Introduction to the Study of Insects

THE STRUCTURE AND LIFE-HISTORY OF THE COCKROACH (PERIPLANETA ORIENTALIS) An Introduction to the Study of Insects

STUDIES IN COMPARATIVE ANATOMY. I.—THE SKULL OF THE CROCODILE . A Manual for Students. By Professor L. C. Miall . 8vo, 2 s. 6 d. II.—THE ANATOMY OF THE INDIAN ELEPHANT . By Professor L. C. Miall and F. Greenwood . 8vo, 5 s. III.—THE COCKROACH: An Introduction to the Study of Insects. By Professor L. C. Miall and A. Denny . 8vo, 7 s. 6 d. IV.—MEGALICHTHYS; A Ganoid Fish of the Coal Measures. By Professor L. C. Miall ( In preparation )....

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PREFACE.

PREFACE.

That the thorough study of concrete animal types is a necessary preliminary to good work in Zoology or Comparative Anatomy will now be granted by all competent judges. At a time when these subjects, though much lectured upon, were rarely taught, Döllinger, of Würzburg, found out the right way. He took young students, often singly, and made them master such animal types as came to hand, thereby teaching them how to work for themselves, and fixing in their minds a nucleus of real knowledge, around

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Malpighi on the Silkworm.

Malpighi on the Silkworm.

Malpighi’s treatise on the Silkworm (1669) is an almost faultless essay in a new field. No Insect—hardly, indeed, any animal—had then been carefully described, and all the methods of work had to be discovered. “This research,” says Malpighi, “was extremely laborious and tedious” (it occupied about a year) “on account of its novelty, as well as the minuteness, fragility, and intricacy of the parts, which required a special manipulation; so that when I had toiled for many months at this incessant

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Swammerdam on the Honey Bee.

Swammerdam on the Honey Bee.

Swammerdam’s great posthumous work, the Biblia Naturæ, contains about a dozen life-histories of Insects worked out in more or less detail. Of these the May-fly (published during the author’s life-time, in 1675) is the most famous; that on the Honey Bee the most elaborate. Swammerdam was ten years younger than Malpighi, and knew Malpighi’s treatise on the Silkworm—a not inconsiderable advantage. His working-life as a naturalist comes within the ten years between 1663 and 1673; and this short spac

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Lyonnet on the Goat Moth.

Lyonnet on the Goat Moth.

In Lyonnet’s memoir on the larva of the Goat Moth (Traité Anatomique de la Chenille qui ronge le bois de Saule, 1760 4 ) we must not look for the originality of Malpighi, nor for the wide range of Swammerdam. One small thing is attempted, and this is accomplished with unerring fidelity and skill. There is something of display in the delineation of the four thousand and forty-one muscles of the Caterpillar, and the author’s skill as a dissector is far beyond his knowledge of animals, whether live

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Straus-Dürckheim on the Cockchafer.

Straus-Dürckheim on the Cockchafer.

In beauty and exact fidelity Straus-Dürckheim’s memoir on the Cockchafer (Considérations Générales sur l’Anatomie Comparée des Animaux Articulés, auxquelles on a joint l’Anatomie Descriptive du Melolontha vulgaris, 1828) rivals the work of Lyonnet. Insect Anatomy was no longer a novel subject in 1828, but Straus-Dürckheim was able to treat it in a new way. Writing under the immediate influence of Cuvier, he sought to apply that comparative method, which had proved so fertile in the hands of the

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Later Insect Anatomists.

Later Insect Anatomists.

It is impossible even to glance at the many anatomists who have illustrated the structure of Insects by studies, less simple in plan, but not less profitable to science, than those of the monographers. If we attempt to select two or three names for express mention, it is with a conviction that others are left whom the student is bound to hold in equal honour. Dufour 5 laboured, not unsuccessfully, to construct a General Anatomy of Insects, which should combine into one view a crowd of particular

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Characters of Arthropoda.

Characters of Arthropoda.

Arthropoda are in general readily distinguished from other animals by their jointed body and limbs. In many Annelids the body is ringed, and each segment bears a pair of appendages, but these appendages are soft, and never articulated. The integument of an Arthropod is stiffened by a deposit of the tough, elastic substance known as Chitin, which resembles horn in appearance, though very different in its chemical composition. In marine Arthropoda, as well as in many Myriopoda and Insects, additio

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Characters of Insects.

Characters of Insects.

Insects are distinguished from other Arthropoda by the arrangement of the segments of the body into three plainly marked regions—head, thorax, and abdomen; by the three pairs of ambulatory legs carried upon the thorax; by the single pair of antennæ; and by the tracheal respiration. Myriopods and Arachnida have no distinct thorax. Most Crustacea have two pairs of antennæ, while in Arachnida antennæ are wanting altogether. Crustacea, if they possess special respiratory organs at all, have branchiæ

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Orders of Insects.

Orders of Insects.

The orders of Insects are usually defined with reference to the degree of metamorphosis and the structure of the parts of the mouth. Five of the orders (3, 5–8) in the table on page 9 undergo complete metamorphosis, and during the time of most rapid change the insect is motionless. In the remaining orders (1, 2, 4) there is either no metamorphosis ( Thysanura ), or it is incomplete— i.e. , the insect is active in all stages of growth. Among these three orders we readily distinguish the minute a

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Further Definition of Cockroaches.

Further Definition of Cockroaches.

In the large order of Orthoptera, which includes Earwigs, Praying Insects, Walking Sticks, Grasshoppers, Locusts, Crickets, White Ants, Day-flies, and Dragon-flies, the family of Cockroaches is defined as follows:— Family Blattina . Body usually depressed, oval. Pronotum shield-like. Legs adapted for running only. Wing-covers usually leathery, opaque, overlapping (if well developed) when at rest, anal area defined by a furrow (fig. 4). Head declivent, or sloped backwards, retractile beneath the

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Range.

Range.

The common Cockroach is native to tropical Asia , 14 and long ago made its way by the old trade-routes to the Mediterranean countries. At the end of the sixteenth century it appears to have got access to England and Holland, and has gradually spread thence to every part of the world. Perhaps the first mention of this insect in zoological literature occurs in Moufet’s Insectorum Theatrum (1634), where he speaks of the Blattæ as occurring in wine cellars, flour mills, &amp;c., in England. It i

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Food and Habits.

Food and Habits.

As to the food of Cockroaches, we can hardly except any animal or vegetable substance from the long list of their depredations. Bark, leaves, the pith of living cycads, paper, woollen clothes, sugar, cheese, bread, blacking, oil, lemons, ink, flesh, fish, leather, the dead bodies of other Cockroaches, their own cast skins and empty egg-capsules, all are greedily consumed. Cucumber, too, they will eat, though it disagrees with them horribly. In the matter of temperature they are less easy to plea

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The Cockroach a persistent type.

The Cockroach a persistent type.

The Cockroach is historically one of the most ancient, and structurally one of the most primitive, of our surviving insects. Its immense antiquity is shown by the fact that so many Cockroaches have been found in the Coal Measures, where about eighty species have been met with. The absence of well-defined stages of growth, such as the soft-bodied larva or inactive pupa, the little specialised wings and jaws, the simple structure of the thorax, the jointed appendages carried on the end of the abdo

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Life-History.

Life-History.

The eggs of the Cockroach are laid sixteen together in a large horny capsule. This capsule is oval, with roundish ends, and has a longitudinal serrated ridge, which is uppermost while in position within the body of the female. The capsule is formed by the secretion of a “colleterial” gland, poured out upon the inner surface of a chamber (vulva) into which the oviducts lead. The secretion is at first fluid and white, but hardens and turns brown on exposure to the air. In this way a sort of mould

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Sexual Differences.

Sexual Differences.

Male Cockroaches are readily distinguished from the females by the well-developed wings and wing-covers. They are also slighter and weaker than the females; their terga and sterna are not so much thickened; their alimentary canal is more slender, and they feed less greedily (the crop of the male is usually only half-full of food). They stand higher on their legs than the females, whose abdomen trails on the ground. The external anatomical differences of the sexes may be tabulated thus:—...

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Parasites.

Parasites.

We have before us a long list of parasites 26 which infest the Cockroach. There is a conferva, an amœba, several infusoria, nematoid worms (one of which migrates to and fro between the rat and the Cockroach), a mite, as well as hymenopterous and coleopterous Insects. The Cockroach has a still longer array of foes, which includes monkeys, hedgehogs, pole-cats, cats, rats, birds, chamæleons, frogs, and wasps, but no single friend, unless those are reckoned as friends which are the foes of its foes

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Names in common use.

Names in common use.

A few lines must be added upon the popular and scientific names of this insect. Etymologists have found it hard to explain the common English name, which seems to be related to cock and roach , but has really nothing to do with either. The lexicographers usually hold their peace about it, or give derivations which are absurd. Mr. James M. Miall informs us that “ Cockroach can be traced to the Spanish cucarácha , a diminutive form of cuco or coco (Lat. coccum , a berry). Cucarácha is used also of

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Uses.

Uses.

Of the uses to which Cockroaches have been put we have little to say. They constitute a popular remedy for dropsy in Russia, and both cockroach-tea and cockroach-pills are known in the medical practice of Philadelphia. Salted Cockroaches are said to have an agreeable flavour which is apparent in certain popular sauces. The Outer Skeleton. SPECIAL REFERENCES. Krukenberg. Vergleichend-Physiologische Vorträge. IV.—Vergl. Physiologie der Thierischen Gerüstsubstanzen. (1885.) [Chemical Relations of C

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Chitin.

Chitin.

When the skin of an Insect is boiled successively in acids, alkalies, alcohol, and ether, an insoluble residue known as Chitin (C 15 H 26 N 2 O 10 ) is obtained. It may be recognised and sufficiently separated by its resistance to boiling liquor potassæ. Chitin forms less than one-half by weight of the integument, but it is so coherent and uniformly distributed that when isolated by chemical reagents, and even when cautiously calcined, it retains its original organised form. The colour which it

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The Chitinous Cuticle.

The Chitinous Cuticle.

Fig. 8.—Diagram of Insect integument, in section. bm , basement membrane; hyp , hypodermis, or chitinogenous layer; ct , ct ′, chitinous cuticle; s , a seta. The chitinous exoskeleton is rather an exudation than a true tissue. It is not made up of cells, but of many superposed laminæ, secreted by an underlying epithelium, or “chitinogenous layer.” This consists of a single layer of flattened cells, resting upon a basement membrane. A cross-section of the chitinous layer, or “cuticle,” examined w

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Parts of a Somite.

Parts of a Somite.

Audouin’s laborious researches into the exoskeleton of Insects 37 resulted in a nomenclature which has been generally adopted. He divides each somite (segment) into eight pieces, grouped in pairs—viz., terga (dorsal plates), sterna (ventral plates), epimera (adjacent to the terga), and episterna (adjacent to the sterna). While admitting the usefulness of these terms, we must warn the reader not to suppose that this subdivision is either normal or primitive. The eight-parted segment exists in no

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Somites of the Cockroach.

Somites of the Cockroach.

The exoskeleton of the Cockroach is divisible into about seventeen segments, which are grouped into three regions, as follows:— It is a strong argument in favour of this estimate that many Insects, at the time when segmentation first appears, possess seventeen segments . 40 The procephalic lobes, from which a great part of the head, including the antennæ, is developed, are often counted as an additional segment . 41 The limbs, which in less specialised Arthropoda are carried with great regularit

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Head; Central Parts.

Head; Central Parts.

Fig. 13.—Front of Head. × 10. The head of the Cockroach, as seen from the front, is pear-shaped, having a semi-circular outline above, and narrowing downwards. A side-view shows that the front and back are flattish, while the top and sides are regularly rounded. In the living animal the face is usually inclined downwards, but it can be tilted till the lower end projects considerably forward. The mouth, surrounded by gnathites or jaws, opens below. On the hinder surface is the occipital foramen,

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Antennæ; Eyes.

Antennæ; Eyes.

Fig. 18.—Base of Antenna of Male (to left) and Female (to right). × 24. A pair of antennæ spring from the front of the head. In the male of the common Cockroach they are a little longer than the body; in the female rather shorter. From seventy-five to ninety joints are usually found, and the three basal joints are larger than the rest. Up to about the thirtieth, the joints are about twice as wide as long; from this point they become more elongate. The joints are connected by flexible membranes,

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Mouth-parts of the Cockroach.

Mouth-parts of the Cockroach.

Before entering upon a full description of the mouth-parts of the Cockroach, which present some technical difficulties, the beginner in Insect anatomy will find it useful to get a few points of nomenclature fixed in his memory. Unfortunately, the terms employed by entomologists are at times neither convenient nor philosophical. There are three pairs of jaws, disposed behind the labrum, as in the diagram:— Fig. 19.—Diagram of Cockroach Jaws, in horizontal section. The mandible is undivided in

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Functions of the Antennæ and Mouth-parts.

Functions of the Antennæ and Mouth-parts.

We must now shortly consider the functions of the parts just described. The antennæ have long been regarded as sense-organs, and even the casual observer can hardly fail to remark that they are habitually used by the Insect to gain information concerning its immediate surroundings. Long antennæ, such as those of the Cockroach, are certainly organs of touch, but it has been much disputed whether they may not also be the seat of some special sense, and if so, what that sense may be. Several author

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Comparison of Mouth-parts in different Insects.

Comparison of Mouth-parts in different Insects.

The jaws of the Cockroach form an excellent standard of comparison for those of other Insects, and we shall attempt to illustrate the chief variations by referring them to this type . 56 Mouth-parts are so extensively used in the classification of Insects that every entomologist ought to have a rational as well as a technical knowledge of their comparative structure. No part of Insect anatomy affords more striking examples of adaptive modification. In form, size, and mode of application the jaws

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Composition of Head.

Composition of Head.

In all Insects fusion of the primitive elements of the head begins so early and is carried so far, that it is extremely difficult to discover the precise way in which they are fitted together. The following facts have been ascertained respecting the development of the parts in question. At a very early stage of embryonic life the body of the Insect becomes divided into a series of segments, which are at fewest fourteen (in some Diptera), while they are not known to exceed seventeen . 62 Each seg

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Neck.

Neck.

The neck is a narrow cylindrical tube, with a flexible wall strengthened by eight plates, the cervical sclerites, two of which are dorsal, two ventral, and four lateral. The dorsal sclerites lie immediately behind the head (fig. 14 ); they are triangular, and closely approximated to the middle line. The inferior plates (fig. 27) resemble segments of chitinous hoops set transversely, one behind the other, rather behind the dorsal sclerites, and close behind the submentum. There are two lateral s

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Thorax.

Thorax.

Fig. 27.—Ventral Plates of Neck and Thorax of Male Cockroach. I, prosternum; II, mesosternum; III, metasternum. × 6. The elements of the thoracic exoskeleton are simpler in the Cockroach than in Insects of powerful flight, where adaptive changes greatly obscure the primitive arrangement. There are three segments, each defended by a dorsal plate ( tergum ) and a ventral plate ( sternum ). The sterna are often divided into lateral halves. Of the three terga the first ( pronotum ) is the la

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Thoracic Appendages. Legs; Wings.

Thoracic Appendages. Legs; Wings.

Fig. 28.—The three Thoracic Legs of a Female Cockroach. I, s , sternum; cx , coxa; tr , trochanter; fe , femur; tb , tibia; ta , tarsus. In III A the coxa is abducted, and the joints a (episternum) and b slightly separated. × 4. Three pairs of legs are attached to the thoracic segments; they regularly increase in size from the first to the third, but hardly differ except in size; the peculiar modifications which affect the fore pair in predatory and burrowing Orthoptera ( Mantis , Gr

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Origin of Insect Wings.

Origin of Insect Wings.

The structure of the wing testifies to its origin as a fold of the chitinous integument. It is a double lamina, which often encloses a visible space at its base. The nervures, with their vessels and tracheal tubes, lie between the two layers, which, except at the base, are in close contact. Oken termed the wings of an Insect “aerial gills,” and this rather fanciful designation is in some degree justified by their resemblance to the tracheal gills of such aquatic larvæ as those of Ephemeridæ, Per

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Abdomen.

Abdomen.

In the abdomen of the female Cockroach eight terga (1–7; 10) are externally visible. Two more (8, 9) are readily displayed by extending the abdomen; they are ordinarily concealed beneath the seventh tergum. The tenth tergum is notched in the middle of its posterior margin. A pair of triangular “podical plates,” which lie on either side of the anus, and towards the dorsal surface, have been provisionally regarded by Prof. Huxley as the terga of an eleventh segment. Seven abdominal sterna (1–7) ar

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Structure of Insect Muscles.

Structure of Insect Muscles.

The muscles of the Cockroach, when quite fresh, appear semi-transparent and colourless. If subjected to pressure or strain they are found to be extremely tender. Alcohol hardens and contracts them, while it renders them opaque and brittle. The minute structure of the voluntary or striped muscular fibres of Vertebrates is described in common text-books . 84 Each fibre is invested by a transparent elastic sheath, the sarcolemma, and the space within the sarcolemma is subdivided by transverse membr

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General Arrangement of Insect Muscles.

General Arrangement of Insect Muscles.

The arrangement of the muscles in an Insect varies greatly according to situation and mode of action. Some of the abdominal muscles consist solely of straight parallel bundles, while the muscles of the limbs usually converge to tendinous insertions. In certain larvæ, where the segments show hardly any differentiation, the muscles form a sheet which covers the whole body, and is regularly segmented in correspondence with the exo-skeleton. As the movements of the body and limbs become more varied

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Muscles of the Cockroach.

Muscles of the Cockroach.

The following short notes on the muscles of the Cockroach, aided by reference to the figures, will render the more noteworthy features intelligible. A very lengthy description, far beyond our space or the reader’s patience, would be required to explain in detail the musculature of the head, limbs, and other specialised regions. Sternal Muscles of Abdomen. —The longitudinal sternal muscles (fig. 34) form a nearly continuous transversely seg mented sheet, covering the ventral surface between the f

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Insect Mechanics.

Insect Mechanics.

The mechanics of Insect movements require exposition and illustration far beyond what is possible in a book like this. Even the elaborate dissections of Lyonnet and Straus-Dürckheim are not a sufficient basis for a thorough treatment of the subject, and until we possess many careful dissections, made by anatomists who are bent upon mastering the action of the parts, our views must needs be vague and of doubtful value. Zoologists of great eminence have been led into erroneous statements when they

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Muscular Force of Insects.

Muscular Force of Insects.

The force exerted by Insects has long been remarked with surprise, and it is a fact familiar, not only to naturalists, but to all observant persons, that, making allowance for their small size, Insects are the most powerful of common animals. Popular books of natural history give striking and sometimes exaggerated accounts of the prodigious strength put forth by captive Insects in their efforts to escape. Thus we are told that the flea can draw 70 or 80 times its own weight . 87 The Cockchafer i

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The Fat-body.

The Fat-body.

Adhering to the inner face of the abdominal wall is a cellular mass, which forms an irregular sheet of dense white appearance. This is the fat-body. Its component cells are polygonal, and crowded together. When young they exhibit nuclei and vacuolated protoplasm, but as they get older the nuclei disappear, the cell-boundaries become indistinct, and a fluid, loaded with minute refractive granules , 98 takes the place of the living protoplasm. Rhombohedral or hexagonal crystals, containing uric ac

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The Cœlom.

The Cœlom.

The fat-body is in reality, as development shows, the irregular cellular wall of the cœlom, or perivisceral space. Through this space courses the blood, flowing in no defined vessels, but bathing all the walls and viscera. In other words, the fat-body is an aggregation of little-altered mesoblast-cells, excavated by the cœlom, the rest of the mesoblast having gone to form the muscular layers of the body-wall and of the digestive tube. The Nervous System and Sense Organs. SPECIAL REFERENCES. Newp

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General Anatomy of Nervous Centres.

General Anatomy of Nervous Centres.

The nervous system of the Cockroach comprises ganglia and connectives , 100 which extend throughout the body. We have first, a supra-œsophageal ganglion, or brain, a sub-œsophageal ganglion, and connectives which complete the œsophageal ring. All these lie in the head; behind them, and extending through the thorax and abdomen, is a gangliated cord, with double connectives. The normal arrangement of the ganglia in Annulosa, one to each somite, becomes more or less modified in Insects by coalescen

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Internal Structure of Ganglia.

Internal Structure of Ganglia.

Microscopic examination of the internal structure of the nerve-cord reveals a complex arrangement of cells and fibres. The connectives consist almost entirely of nerve-fibres, which, as in Invertebrates generally, are non-medullated. The ganglia include (1) rounded, often multipolar, nerve-cells; (2) tortuous and extremely delicate fibres collected into intricate skeins; (3) commissural fibres, and (4) connectives. The chief fibrous tracts are internal, the cellular masses outside them. A relati

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Median Nerve-Cord.

Median Nerve-Cord.

Lyonnet , 103 Newport , 104 and Leydig 105 have found in large Insects a system of median nerves, named respiratory (Newport) or sympathetic (Leydig). These nerves do not form a continuous cord extending throughout the body, but take fresh origin in each segment from the right and left longitudinal commissures alternately. The median nerve lies towards the dorsal side of the principal nerve-cord, crosses over the ganglion next behind, and receives a small branch from it. Close behind the ganglio

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Stomato-gastric Nerves.

Stomato-gastric Nerves.

Fig. 44.—Stomato-gastric Nerves of Cockroach. fr.g. , frontal ganglion; at. , antennary nerve; conn. , connective; pa.g. , paired ganglia; r.n. , recurrent nerve; v.g. , ventricular ganglion. In the Cockroach the stomato-gastric nerves found in so many of the higher Invertebrates are conspicuously developed. From the front of each œsophageal connective, a nerve passes forwards upon the œsophagus, outside the chitinous crura of the tentorium. Each nerve sends a branch downwards to th

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Internal Structure of Brain.

Internal Structure of Brain.

Fig. 45.—A, lobes of the brain of the Cockroach, seen from within; c , cauliculus; p , peduncle; t , trabecula. B, ditto, from the front; ocx , outer calyx; icx , inner calyx. C, ditto, from above. Copied from E. T. Newton. The minute structure of the brain has been investigated by Leydig, Dietl, Flögel, and others, and exhibits an unexpected complexity. It is as yet impossible to reduce the many curious details which have been described to a completely intelligible account. The physiolog

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Sense Organs. The Eye of Insects.

Sense Organs. The Eye of Insects.

Fig. 50.—Plan of Eye of Cockroach, showing the number of facets along the principal diameters. as , antennary socket. The sense organs of Insects are very variable, both in position and structure. Three special senses are indicated by transparent and refractive parts of the cuticle, by tense membranes with modified nerve-endings, and by peculiar sensory rods or filaments upon the antennæ. These are taken to be the organs respectively of sight, hearing, and smell. Other sense organs, not as

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Sense of Smell in Insects.

Sense of Smell in Insects.

The existence of a sense of smell in Insects has probably never been disputed. Many facts of common observation prove that carrion-feeders, for example, are powerfully attracted towards putrid animal substances placed out of sight. The situation of the olfactory organs has only been ascertained by varied experiments and repeated discussion. Rosenthal, in 1811, and Lefebvre, in 1838, indicated the antennæ as the organs of smell, basing their conclusions upon physiological observations made upon l

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Sense of Taste in Insects.

Sense of Taste in Insects.

F. Will 119 gives an account of many authors who have investigated with more or less success the sense organs of various Insects. He relates also the results of his own experiments, and gives anatomical details of the sensory organs of the mouth in various Hymenoptera. Wasps, flying at liberty, were allowed to visit and taste a packet of powdered sugar. This was left undisturbed for some hours, and then replaced by alum of the same appearance. The Wasps attacked the alum, but soon indicated by d

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Sense of Hearing in Insects.

Sense of Hearing in Insects.

The auditory organs of Insects and other Arthropoda are remarkable for the various parts of the body in which they occur. Thus they have been found in the first abdominal segment of Locusts, and in the tibia of the fore-leg of Crickets and Grasshoppers, and more questionable structures with peculiar nerve-endings have been described as occurring in the hinder part of the abdomen of various larvæ ( Ptychoptera , Tabanus , &amp;c ). The auditory organ of Decapod Crustacea is lodged in the base

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The Alimentary Canal.

The Alimentary Canal.

The alimentary canal of the Cockroach measures about 2 3 / 4 inches in length, and is therefore about 2 3 / 4 times the length of the body. In herbivorous Insects the relative length of the alimentary canal may be much greater than this; it is five times the length of the body in Hydrophilus. Parts of the canal are specialised for different digestive offices, and their order and relative size are given in the following table:— Fig. 56.—Alimentary Canal of Cockroach. × 2. The principal appenda

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Appendages. The Salivary Glands.

Appendages. The Salivary Glands.

The three principal appendages of the alimentary canal of the Cockroach are outgrowths of the three primary divisions of the digestive tube; the salivary glands are diverticula of the stomodæum, the cæcal tubes of the mesenteron, and the Malpighian tubules of the proctodæum. Fig. 71.—Salivary Glands and Receptacle, right side. The arrow marks the opening of the common duct on the back of the lingua. A , side view of lingua; B , front view of lingua. A large salivary gland and reservoir lie on

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The Cæcal Tubes.

The Cæcal Tubes.

There are eight (sometimes fewer) cæcal tubes arranged in a ring round the fore end of the chylific stomach; they vary in length, the longer ones, which are about equal to the length of the stomach itself, usually alternating with shorter ones, though irregularities of arrangement are common. The tubes are diverticula of the stomach and lined by a similar epithelium. In the living animal they are sometimes filled with a whitish granular fluid. Similar cæcal tubes, sometimes very numerous and den

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The Malpighian Tubules.

The Malpighian Tubules.

The Malpighian tubules mark the beginning of the small intestine, to which they properly belong. They are very numerous (60–70) in the Cockroach, as in Locusts, Earwigs, and Dragon-flies; and unbranched, as in most Insects. They are about ·8 inch in length, and ·002 inch in transverse diameter, so that they are barely visible to the naked eye as single threads. In larvæ about one-fifth of an inch long, Schindler 130 found only eight long tubules, the usual number in Thysanura, Anoplura, and Term

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Digestion of Insects.

Digestion of Insects.

The investigation of the digestive processes in Insects is work of extreme difficulty, and it is not surprising that much yet remains to be discovered. Plateau has, however, succeeded in solving some of the more important questions, which, before his time, had been dealt with in an incomplete or otherwise unsatisfactory way. The experiments of Basch, though now superseded by Plateau’s more trustworthy results, deserve notice as first attempts to investigate the properties of the digestive fluids

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Circulation of Insects.

Circulation of Insects.

A very long chapter might be written upon the views advanced by different writers as to the circulation of Insects. Malpighi first discovered the heart or dorsal vessel in the young Silkworm. His account is tolerably full and remarkably free from mistakes. The heart of the Silkworm, he tells us, extends the whole length of the body, and its pulsations are externally visible in young larvæ. He supposed that contraction is effected by muscular fibres, but these he could not distinctly see. The tub

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Heart of the Cockroach.

Heart of the Cockroach.

The heart of the Cockroach is a long, narrow tube, lying immediately beneath the middle line of the thorax and abdomen. It consists of thirteen segments (fig. 73), which correspond to three thoracic and ten abdominal somites. Each segment, as a rule, ends behind in a conspicuous fold which projects backwards from the dorsal surface; immediately in front of this are two lateral lobes. The median lobe passes into the angle between two adjacent terga, and is continuous with the dorsal wall of the s

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Pericardial Diaphragm and Space.

Pericardial Diaphragm and Space.

The heart lies in a pericardial chamber, which is bounded above by the terga and the longitudinal tergal muscles; below by a fenestrated membrane, the pericardial diaphragm. The intermediate space, which is of inconsiderable depth, is nearly filled by a cellular mass laden with fat, and resembling the fat-body. The pericardial diaphragm, or floor of the pericardium, is continuous, except for small oval openings scattered over its surface. It consists of loosely interwoven fibres, interspersed wi

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Circulation of the Cockroach.

Circulation of the Cockroach.

The pulsations of the heart are rhythmical and usually frequent, the number of beats in a given time varying with the species, the age, and especially with the degree of activity or excitement of the Insect observed . 143 Cornelius 144 watched the pulsations in a white Cockroach immediately after its change of skin, and reckoned them at eighty per minute; but he remarks that the Insect was restless, and that the beats were probably accelerated in consequence. In the living Insect a wave of contr

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Blood of the Cockroach.

Blood of the Cockroach.

The blood of the Cockroach may be collected for examination by cutting off one of the legs, and wiping the cut end with a cover-slip. It abounds in large corpuscles, each of which consists of a rounded nucleus invested by protoplasm. Amœboid movements may often be observed, and dividing corpuscles are occasionally seen. Crystals may be obtained by evaporating a drop of the blood without pressure; they form radiating clusters of pointed needles. The fresh-drawn blood is slightly alkaline; it is c

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Respiratory Organs of Insects.

Respiratory Organs of Insects.

Fig. 77.—Tracheal System of Cockroach. Side view of head seen from without, introducing the chief branches of the left half. × 15. The respiratory organs of Insects consist of ramified tracheal tubes, which communicate with the external air by stigmata or spiracles. Of these spiracles the Cockroach has ten pairs—eight in the abdomen and two in the thorax. The first thoracic spiracle lies in front of the mesothorax, beneath the edge of the tergum; the second is similarly placed in front of th

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Tracheal Tubes.

Tracheal Tubes.

The accompanying figures sufficiently explain the chief features of the tracheal system of the Cockroach, so far as it can be explored by simple dissection. Leaving them to tell their own tale, we shall pass on to the minute structure of the air-tubes, the spiracles, and the physiology of Insect respiration. The tracheal wall is a folding-in of the integument, and agrees with it in general structure. Its inner lining, the intima, is chitinous, and continuous with the outer cuticle. It is secrete

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Tracheal Thread.

Tracheal Thread.

Fig. 84.—Intima (chitinous lining) of a large tracheal tube. The spiral thread divides here and there. Copied from MacLeod, loc. cit., fig. 9. In the finest tracheal tubes (·0001 in. and under) the intima is to all appearance homogeneous. In wider tubes it is strengthened by a spiral thread, which is denser, more refractive, and more flexible than the intervening membrane. The thread projects slightly into the lumen of the tube, and is often branched. It is interrupted frequently, each len

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The Spiracles.

The Spiracles.

The spiracles of the Cockroach are by no means of complicated structure, but their small size, and the differences between one spiracle and another, are difficulties which cost some pains to overcome. Fig. 85.—First Thoracic Spiracle (left side), seen from the outside. × 70. V , valve; I , setose lining of valve (mouth of tracheal tube) × 230. The occlusor muscle is shown. The arrow indicates the direction of air entering the spiracle. In the natural position this spiracle is set ob

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Mechanism of Respiration.

Mechanism of Respiration.

In animals with a complete circulation, aërated blood is diffused throughout the body by means of arteries and capillaries, which deliver it under pressure at all points. Such animals usually possess a special aërating chamber (lung or gill), where oxygen is made to combine with the hæmoglobin of the blood. It is otherwise with Insects. Their blood escapes into great lacunæ, where it stagnates, or flows and ebbs sluggishly, and a diffuse form of the internal organs becomes necessary for their fr

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Respiratory Movements of Insects.

Respiratory Movements of Insects.

By FÉLIX PLATEAU, Professor in the University of Ghent. The respiratory movements of large Insects are in general very apparent, and many observers have said something about what they have seen in various species. It is only since the publication of Rathke’s memoir, however, that precise views have been gained as to the mechanism of these movements. This remarkable work, treating of the respiratory movements in Insects, the movable skeletal plates, and the respiratory muscles characteristic of a

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Respiratory Activity of Insects.

Respiratory Activity of Insects.

The respiratory activity of Insects varies greatly. Warmth, feeding, and movement are found to increase the frequency of their respirations, and also the quantity of carbonic acid exhaled. In Liebe’ s 157 experiments a Carabus produced ·24 mgr. of carbonic acid per hour in September, but only ·09 mgr. per hour in December. A rise of temperature raised the product temporarily to twice its previous amount; but when the same insect was kept under experiment for several days without food, the amount

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Origin of Tracheal Respiration.

Origin of Tracheal Respiration.

Kowalewsky, Bütschli, and Hatschek have described the first stages of development of the tracheal system. Lateral pouches form in the integument; these send out anterior and posterior extensions, which anastomose and form the longitudinal trunks. The tracheal ramifications are not formed by a process of direct invagination, but by the separation of chitinogenous cells, which cohere into strings, and then form irregular tubules. The cells secrete a chitinous lining, and afterwards lose their dist

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Female Reproductive Organs.

Female Reproductive Organs.

Fig. 94.—Female Reproductive Organs. Od , oviduct; CG , colleterial gland. × 14. The ovaries of the two sides of the body are separated, as in most Insects, and consist on each side of eight tubes, four dorsal and four ventral, which open into the inner side of a common oviduct. The two oviducts unite behind, and form a very short uterus. Tracheæ and fat-cells tie the ovarian tubes of each side together into a spindle-shaped bundle. Each tube is about ·4 in. long, and has a beaded appearance

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Male Reproductive Organs.

Male Reproductive Organs.

The male reproductive organs of Insects, in spite of very great superficial diversity, are reducible to a common type, which is exemplified by certain Coleoptera. The essential parts are (1) the testes , which in their simplest form are paired, convoluted tubes; more commonly they branch into many tubules or vesiculæ, while they may become consolidated into a single organ; (2) long coiled vasa deferentia , opening into or close to (3) paired vesiculæ seminales , which discharge into (4) the ejac

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The Embryonic Development of the Cockroach. 174

The Embryonic Development of the Cockroach. 174

By JOSEPH NUSBAUM, Magister of Zoology, Warsaw. The development of the Cockroach is by no means an easy study. It costs some pains to find an accessible place in which the females regularly lay their eggs, and the opaque capsule renders it hard to tell in what stage of growth the contained embryos will be found. Accordingly, though the development of the Cockroach has lately attracted some observers, the inexperienced embryologist will find it more profitable to examine the eggs of Bees, of Aphi

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Post-embryonic Development.

Post-embryonic Development.

At the time of hatching the Cockroach resembles its parent in all essentials, the wings being the only organs which are developed subsequently, not as entirely new parts, but as extensions of the lateral edges of the thoracic terga. The mode of life of the young Cockroach is like that of the adult, and development may be said to be direct, or with only a trifling amount of metamorphosis. In the Thysanura even this small post-embryonic change ceases to appear, and the Insect, when it leaves the e

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Animal Metamorphoses.

Animal Metamorphoses.

To investigate the causes of metamorphosis, let us select from the same sub-kingdom two animals as unlike as possible with respect to the amount of post-embryonic change to which they are subject. We can find no better examples than Amphioxus and the Chick. The newly-hatched Amphioxus is a small, two-layered, hollow sac, which moves through the sea by the play of cilia which project everywhere from its outer surface. It is a Gastræa, a little simpler than the Hydra, and far simpler than a Jelly-

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The Genealogy of Insects.

The Genealogy of Insects.

To construct from embryological and other data a chart of the descent of Insects, and of the different orders within the class, is an attempt too hazardous for a student’s text-book . 192 A review of the facts of Arthropod development led Balfour 193 to conclude that the whole of the Arthropoda cannot be united in a common phylum. The Tracheata are probably “descended from a terrestrial Annelidan type related to Peripatus ... . The Crustacea, on the other hand, are clearly descended from a Phyll

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CHAPTER XI.

CHAPTER XI.

The Cockroach of the Past. By S. H. SCUDDER, of the U.S. Geological Survey. Small and large intestines. Ref. —Leidy, Trans. Amer. Phil. Soc., Vol. X., p. 244, pl. xi. (1852). Plagiotoma (Bursaria) blattarum , Stein. Infusoria. Rectum. Ref. —Stein, Sitzb. d. königl. Böhm. Ges., 1860, pp. 49, 50. Lophomonas Blattarum , Stein. Infusoria. Rectum. Ref. —Stein (loc. cit.); Bütschli, Zeits. f. wiss. Zool., Bd. XXX., p. 258, plates xiii., xv. (1878). L. striata , Bütschli. Infusoria. Rectum. Ref. —Bütsc

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