wesw < 9 O622S9E0 LOZ: ¢€ HMA OLNO¥O! 4O ALISYIAINN ASV4SN ADO100Z 3 cys a a oe ea a ae Digitized by the Internet Archive in 2010 with funding from University of Toronto http://www.archive.org/details/structurelifehi0Omial ye 4 Ww Aarias ti bow: COCK ROACH Aw Antroduction to the Studp of Ansects : oo \ nsecva ™ STUDIES IN COMPARATIVE ANATOMY—III THE STRUCTURE AND LIFE-HISTORY THE COCKROACH (PERIPLANETA ORIENTALIS) An AIntroduction to the Study of Insects BY L. C. MIALL PROFESSOR OF BIOLOGY IN THE YORKSHIRE COLLEGE, LEEDS AND ALFRED DENNY LECTURER ON BIOLOGY IN THE FIRTH COLLEGE, SHEFFIELD Fo Y 4 4 oa ob ( \ LONDON: LOVELL REEVE & CO. LEEDS: RICHARD JACKSON 1886 STUDIES IN COMPARATIVE ANATOMY. ——¢¢—— I.—THE SKULL OF THE CROCODILE. A Manual for Students. By Professor L. C. Mrauu. 8vo, 2s. 6d. II.—_THE ANATOMY OF THE INDIAN ELEPHANT. By Professor L. C. Mr1att and F. GREENwoop. $8vo, 5s. Ill.—THE COCKROACH: An Introduction to the Study of Insects. By Professor L. C. Miatt and A, Denny. §8vo, 7s. 6d. IV.—_MEGALICHTHYS; A Ganoid Fish of the Coal Measures. By Professor L. C. Mian Un preparation). MAY BE HAD OF LOVELL REEVE & CO., LONDON; RICHARD JACKSON, LEEDS. PREFACH. THatT 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. Ata time when these subjects, though much lectured upon, were rarely taught, Dollinger, of Wiirzburg, 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 which more might crystallise. “What do you want lectures for? Bring any animal and dissect it here,” said he to Baer, then a young doctor longing to work at Comparative Anatomy.* It was Déllinger who trained Purkinje, Pander, Baer, and Agassiz, and such fame cannot be heightened by words of praise. In our own time and country Dollinger’s methods have been practised by Professor Huxley, whose descriptive guides, such as the Elementary Biology and the delightful little book on the Crayfish, now make it easy for every teacher to work on the same lines. From the description of the Cockroach in Huxley’s Anatomy of Invertebrated Animals came the impulse which has encouraged us to treat that type at length. It may easily turn out that in adding some facts and a great many words to his account, we have diluted what was valuable for its concentration. But there are students—those, namely, who intend to give serious attention to Entomology—who will find our explanations deficient rather than excessive in detail. It is our belief and hope that naturalists will some day recoil from their extravagant love of words and names, and turn to * Baer’s account of Déllinger is to be found in the Leben und Schriften von K. E, yon Baer, § 8, PREFACE. structure, development, life-history, and other aspects of the animal world which have points of contact with the life of man. We have written for such as desire to study Insects on this side. Whoever attempts to tell all that is important about a very common animal will feel his dependence upon other workers. Much of what is here printed has been told before. The large number of new figures is, however, some proof that we have worked for ourselves. It is a pleasant duty to offer our thanks for friendly help received. Professor Félix Plateau, of Ghent; Mr. Joseph Nusbaum, of Warsaw ; and Mr. S. H. Scudder, of Cambridge, Massachusetts, have very kindly consented to treat here of those parts of the subject which they have specially illustrated by their own labours.* Mr. E. T. Newton, of the Jermyn Street Museum, has lent us the wood blocks used to illustrate one of his papers on the Brain of the Cockroach. A number of the figures have been very carefully and faithfully drawn for us by Miss Beatrice Boyle, a student in the Yorkshire College. We are much indebted to Dr. Murie, the Librarian of the Linnean Society, for procuring us access to the extensive literature of Insect Anatomy, and for answering not a few troublesome questions. Five articles on the Cockroach were contributed by us to Science Gossip in 1884, and some of the figures were then engraved and published. In issuing a book which has been long in hand, but which can never hope to be complete, we venture to adopt the words already used by Leydig concerning his Lehrbuch der Histologie :—“ Die eigentlich nie fertig wird, die man aber fiir fertig erklaren muss, wenn man nach Zeit und Umstiinden das Moglichste gethan hat.” * Prof. Plateau’s chief communications will be found on pp. 131 and 159; Mr. Nusbaum has furnished the account of the Development of the Cockroach, pp. 180 to 195; and Mr. Scudder the Geological History of the Cockroach, chap. xi.’ CONTENTS. CHAP, PAGE 1.—Wraitincs on Insect ANATOMY 9 I11.—Tue Narurat History or THE CockROAcH ... da” > 1V.—Tue Outer SKELETON ... oa we ae te OR V.—Tue Muscies; tHe Fat-Bopy anpD Ca&Lom ... at gee VI.—TueE Nervous System AND SENSE ORGANS ... a eee VII.—Tue ALIMENTARY CANAL AND ITS APPENDAGES cde AES VIII.—Tue OrGans or CIRCULATION AND ReEsPIRATION (in- cluding a section on the Respiratory Movements of Insects, by Prof. Félix Plateau, of Ghent) ... wehde ITX.—REPRODUCTION ... oo a a 2 = a X.—DEVELOPMENT (including a section on the Embryonic Development of the Cockroach, by Joseph Nusbaum, of Warsaw)... ie Sas ™~— a Pome XI.—TuHeE CockroacH oF THE Past, by 8. H. Scudder, of the U.S. Geological Survey ... df a ... 205 APPENDIX :— PARASITES OF THE COCKROACH. SENSE OF SMELL IN INSECTs. *.* Where the species is not named, it is to be understood that the figures are drawn from the Cockroach. P- ‘ . ' i . Ww ’ Ye ' > . ’ , - ~~ . = STUDIES IN COMPARATIVE ANATOMY.—No. III. THE COCKROACH. CHAPTER I. Writincs on Insecr ANATOMY. MARCELLO MALPIGHI. 1628-1694. JAN SWAMMERDAM. 1637-1680. PIERRE LYONNET. 1707-1789. HERCULE STRAUS-DURCKHEIM. 1790-1865. Tue lovers of minute anatomy have always been specially attracted to Insects; and it is not hard to tell why. No other animals, perhaps, exhibit so complex an organisation condensed into so small a body. We possess, accordingly, a remarkable succession of memoirs on the structure of single Insects, begin- ning with the revival of Anatomy in the 17th century and extending to our own times. The most memorable of these Insect-monographs bear the names of Malpighi, Swammerdam, Lyonnet, and Straus-Diirckheim. 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 and fatiguing task, I was plagued next autumn with fevers and inflammation of the eyes. Nevertheless, such B 2 THE COCKROACH. was my delight in the work, so many unsuspected wonders of nature revealing themselves to me, that I cannot tell it in words.” We must recall the complete ignorance of Insect- anatomy which then prevailed, and remember that now for the first time the dorsal vessel, the tracheal system, the tubular appendages of the stomach, the reproductive organs, and the structural changes which accompany transformation were observed, to give any adequate credit to the writer of this masterly study. Treading a new path, he walks steadily for- ward, trusting to his own sure eyes and cautious judgment. The descriptions are brief and simple, the figures clear, but not rich in detail. There would now be much to add to Malpighi’s account, but hardly anything to correct. The only positive mistakes which meet the eye relate to the number of spiracles and nervous ganglia—mistakes promptly corrected by Swam- merdam. Had the tract De Bombycibus been the one work of its author, this would have kept his memory bright, but it hardly adds to the fame of the anatomist who discovered the cellular structure of the lung, the glandular structure of the liver and kidney, and the sensory papille of the skin, who first saw the blood-corpuscles stream along a vessel, who studied very early and very completely the minute structure of plants and the development of the chick, and whose name is rightfully associated with the mucous layer of the epidermis, the vascular tufts of the kidney, and the follicles of the spleen, as well as with the urinary tubules of Insects. All that we know of Malpighi commands our respect. Pre- cise and rapid in his work, keen to discover points of real interest, never losing himself in details, but knowing when he had done enough, he stands pre-eminent in the crowd of minute anatomists, who are generally faithful in a few things, but very unfit to be made rulers over many things. The last distinct glimpse which we get of him is interesting. Dr. Tancred Robinson, writing to John Ray, from Geneva, April 18th, 1684, tells how he met Malpighi at Bologna. They talked of the origin of fossils, and Malpighi could not contain himself about Martin Lister’s foolish hypothesis that fossils were sports of nature. ‘Just as I left Bononia,” he continues, “I had a lamentable spectacle of Malpighi’s house all in flames, occa- WRITINGS ON INSECT ANATOMY. 3 sioned by the negligence of his old wife. All his pictures, furniture, books, and manuscripts were burnt. I saw him in the very heat of the calamity, and methought I never beheld so much Christian patience and philosophy in any man before; for he comforted his wife, and condoled nothing but the loss of his papers, which are more lamented than the Alexandrian Library, or Bartholine’s Bibliothece, at Copenhagen.” * Swammerdam on the Honey Bee. Swammerdam’s great posthumous work, the Biblia Nature, 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 Silkwerm—a not inconsiderable advantage. His working-life as a naturalist comes within the ten years between 1663 and 1673; and this short space of time was darkened by anxiety about money, as well as by the religious fanaticism, which in the end completely extinguished his activity. The vast amount of highly-finished work which he accomplished in these ten years justifies Boerhaave’s rather rhetorical account of his industry. Unfortunately, Boerhaave, whom we have to thank not only for a useful sketch of Swammerdam’s life, but also for the preservation of most of his writings, was only twelve years old when the great naturalist died, and his account cannot be taken as personal testimony. Swammerdam, he tells us, worked with a simple microscope and several powers. His great skill lay in his dexterous use of scissors. Sometimes he employed tools so fine as to require whetting under the microscope. He was famous for inflated and injected preparations. As to his patience, it is enough to say that he would spend whole days in clearing a single caterpillar. Boerhaave gives us a picture of Swammerdam at work which the reader does not soon forget. “His labours were superhuman. Through the day he observed incessantly, and at night he described and drew what he had seen. By six o’clock in the morning in summer he began to * Correspondence of John Ray, p. 142. 4 THE COCKROACH. find enough light to enable him to trace the minutize of natural objects. He was hard at work till noon, in full sunlight, and bareheaded, so as not to obstruct the light; and his head streamed with profuse sweat. His eyes, by reason of the blaze of light and microscopic toil, became so weakened that he could not observe minute objects in the afternoon, though the light was not less bright than in the morning, for his eyes were weary, and could no longer perceive readily.” Comparing Swammerdam’s account of the Bee with the use- ful and amply illustrated memoir of Girdwoyn (Paris, 1876), it is plain that two centuries have added little to our knowledge of the structure of this type. Much has been made out since 1675 concerning the life-history of Bees, but of what was to be discovered by lens and scalpel, Swammerdam left little indeed to others. It is needless to dwell upon the omissions of so early an explorer, Swammerdam proved by dissection that the queen is the mother of the colony, that the drones are males, and the working-bees neuters; but he did not find out that the neuters are only imperfect females. In this instance, as in some others, Swammerdam’s authority served, long after his death, to delay acceptance of the truth. It is far from a reproach to him that in the Honey Bee he lit upon an almost inexhaustible subject. In the 17th century no one suspected that the sexual economy of any animal could be so complicated as that which has been demonstrated, step by step, in the Honey Bee. 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*) 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 or dead. ‘The dissections of the head are perhaps the most * Copies dated 1762 have a plate representing the microscope and dissecting instru- ments used by the author. WRITINGS ON INSECT ANATOMY, 5 extraordinary feat, and will never be surpassed. Modern treatises on Comparative Anatomy continue to reproduce some of these figures, such as the general view of the viscera, the structure of the leg, and the digestive tract. Nearly the whole interest of the volume lies in the plates, for the text is little more than a voluminous explanation of the figures. It is not without surprise that we find that Lyonnet was an amateur, who had received no regular training either in anatomy or engraving, and that he had many pursuits besides the delineation of natural objects. He was brought up for the Protestant ministry, turned to the bar, and finally became cipher-secretary and confidential translator to the United Pro- vinces of Holland. He is said to have been skilled in eight languages. His first published work in Natural History con- sisted of remarks and drawings contributed to Lesser’s Insect Theology (1742). About the same time, Trembley was prosecuting at the Hague his studies on the freshwater Polyp, and Lyonnet gave him some friendly help in the work. Those who care to turn to the preface of Trembley’s famous treatise (Mémoires pour servir a l'histoire des Polypes d’eau douce, 1744) will see how warmly Lyonnet’s services are acknowledged. He made all the drawings, and engraved eight of them himself, while Trembley is careful to note that he was not only a skilful draughtsman, but an acute and experienced observer. When the work was begun, Lyonnet had never even seen the operation of engraving a plate. Wandelaar, struck by the beauty of his drawings, persuaded him to try what he could do with a burin. His first essay was made upon the figure of a Dragon-fly, next he engraved three Butterflies, and then, without longer appren- ticeship, he proceeded to engrave the plates still required to complete the memoir on Hydra. Lyonnet tells us that the larva of the Goat Moth was not quite his earliest attempt in Insect Anatomy. He began with the Sheep Tick, but suspecting that the subject would not be popular, he made a fresh choice for his first memoir. Enough interest was excited by the Traité Anatomique to call for the fulfilment of a promise made in the preface that the description of the pupa and imago should follow. But though Lyonnet continued for some time to fill his portfolio with drawings and 6 THE COCKROACH. : notes, he never published again. Failing eyesight was one ground of his retirement from work. What he had been able to finish, together with a considerable mass of miscellaneous notes, illustrated by fifty-four plates from his own hand, was published, long after his death, in the Mémoires du Muséum (XVIII.-XX.). Straus-Diirckheim on the Cockchafer. In beauty and exact fidelity Straus-Diirckheim’s memoir on the Cockchafer (Considérations Générales sur Anatomie Comparée des Animaux Articulés, auxquelles on a joint l’ Anatomie Descrip- tive du Melolontha vulgaris, 1828) rivals the work of Lyonnet. Insect Anatomy was no longer a novel subject in 1828, but Straus-Diirckheim was able to treat it ina 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 master, to the Articulate sub-kingdom. This conception was realised as fully as the state of zoology at that time allowed, and the Considérations Génerales count as an important step towards a complete comparative anatomy of Arthropoda. Straus-Diirckheim had at command a great mass of anatomical facts, much of which had been accumulated by his own observations. He systematically compares Insects with other Articulata, Coleoptera with other Insects, and the Cock- chafer with other Coleoptera. Perhaps no one before him had been perfectly clear as to the morphological equivalence of the appendages in all parts of the body of Arthropods, and here he was able to extend the teaching of Savigny. His limitations are those of his time. If in certain sections we find his collection of facts to be meagre, and his generalisations nugatory, we must allow for the progress of the last sixty years—a progress in which Straus-Diirckheim has his share. It is the work of science continually to remake its syntheses, and no work becomes antiquated sooner than morphological generalisation. It is therefore no reproach to Straus-Diirckheim that his treatise should now be chiefly valuable, not as ‘‘ Considérations Générales,” but as the anatomy of the Cockchafer. Long after his theories and explanations have ceased to be instructive, when WRITINGS ON INSECT ANATOMY. | the morphology and physiology of 1828 have become as obsolete as the Ptolemaic astronomy, the naturalist will study these exquisite delineations of Insect-structure with something of the pleasure to be found in examining for the hundredth time a delicate organism familiar to many generations of microscopic observers. The fidelity and love of anatomical detail which characterise the description of the Cockchafer are not less conspicuous in Straus-Diirckheim’s Anatomie Descriptive du Chat (1846). Both treatises have become classical. We have seen how, in Straus-Diirckheim’s hands, Insect anatomy became comparative. New studies—histology, embry- onic development, and palzeontology—have since arisen to com- plicate the task of the descriptive anatomist, and it appears to be no longer possible for one man to complete the history of any animal of elaborate structure and ancient pedigree. As a method of research the monograph has had its day. The path of biological discovery now follows an organ or a function across all zoological boundaries, and it is in the humbler office of biological teaching that the monograph finds its proper use. 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* laboured, not unsuccessfully, to construct a General Anatomy of Insects, which should combine into one view a crowd of particular facts. The modern reader will gratefully acknowledge his industry and the beauty of his drawings, but will now and then complain that his sagacity does not do justice to his diligence. * Dufour. Rech. anat. et phys. sur les Hémiptéres (1833) les Orthoptéres, les Hymenoptéres et les Neuroptéres (1841), et les Diptéres (1851). Mém. de l'Institut, Tom. IV., VII., XI. Also many memoirs in Ann. des Sci. Nat. 8 ’ THE COCKROACH. Newport,* a naturalist of greater weight and interest, is memorable for his skill in minute dissection, for his many curious observations upon the life-history of Insects (see, for example, his memoir on the Oil-beetle), and especially for his early appreciation of the value of embryological study. Leydigt was the first to occupy fully the new field of Insect histology, and point out its resources to the physiologist. In all his works the student finds beauty and exactness of delinea- tion, suggestiveness in explanation. Leydig’s contributions to Insect anatomy and physiology, valuable as they are to the specialist, are not isolated researches, but form part of a new comparative anatomy, based upon histology. Incomplete so vast a work must necessarily remain, but it already extends over considerable sections of the animal kingdom. * Newport. Art. ‘‘ Insecta,” in Cycl. of Anat. and Phys. (1839), besides many special memoirs in the Phil. and Linn. Trans, + Leydig. Vom Bau des Thierischen Korpers (1864), Tafeln zur vergl. Anatomie (1864), Untersuchungen zur Anat. und Histologie der Thiere (1883), &c., besides many special memoirs in Miiller’s Archiv., Zeits, f. wiss. Zool., Nova Acta, ‘ke. CHAPTER II. Tur ZootocicAL Postrion oF THE CocKROACH. Sub-kingdom ARTHROPODA. Class I. Crustacea. >, II. Arachnida. », III. Myriopoda. >» LV. INSECTA. Order 1. Thysanura. >» 2. Orthoptera. Neuroptera. Hemiptera. Coleoptera. Diptera. Lepidoptera. Hymenoptera. SES SU Sok Tue place of the Cockroach in the Animal Kingdom is illus- trated by the above table. It belongs to the sub-kingdom Arthropoda, to the class Insecta, and to the order Orthoptera. 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, additional firmness may be gained by the incorporation of carbonate and phosphate of lime with the chitin. However rigid the integument, may be, it is rendered compatible with energetic movements by its unequal thickening. Along defined, 10 THE COCKROACH : usually transverse lines it remains thin, the chitinous layer, though perfectly continuous, becoming extremely flexible, and allowing a certain amount of deflection or retraction (fig. 1). Fig. 1.—Diagram of Arthropod limb extended, retracted, and flexed. Graber has given a similar figure (Insekten, fig. 8*). The joints of the trunk and limbs may thus resemble stiff tubes. Muscles are attached to their inner surface, and are therefore enclosed by the system of levers upon which they act (fig. 2B). In Vertebrate animals, on the contrary, which possess a true internal skeleton, the muscles clothe the levers (bones) to which B Fig. 2.—Vertebrate and Arthropod joints. A, Vertebrate joint, the skeleton clothed with muscles. B, Arthropod joint, the skeleton enclosing the muscles. they are attached (fig. 2a). The whole outer surface of an Arthropod, including the eyes, auditory membrane (if there is one), and surface-hairs, is chitinised. Chitin may also stiffen ITS ZOOLOGICAL POSITION. 1] the larger tendons, internal ridges and partitions, and the lining membrane of extensive internal cavities, such as the alimentary canal, and the air-tubes of Insects. In most Arthropoda the body is provided with many appen- dages. In Crustacea there are often twenty pairs, but some Myriopoda have not far from two hundred pairs. Some of these may be converted to very peculiar functions; in particular, several pairs adjacent to the mouth are usually appropriated to mastication. One or more pairs of appendages are often trans- formed into antenne. The relative position of the chief organs of the body, viz.:— heart, nerve-cord, and alimentary canal, is constant in Arthro- poda. The heart is dorsal, the nerve-cord ventral, the alimentary canal intermediate. (See fig. 3.) The cesophagus passes between the connectives of the nerve-cord. Not a few other animals, such as Annelids and Mollusca, exhibit the same arrangement. Arthropoda are not known to be ciliated in any part of the body, or in any stage of growth. Another histological pecu- liarity, not quite so universal, is the striation of the muscular fibres throughout the body. In many Invertebrates there are no striated muscles at all, while in Vertebrates only voluntary muscles, as a rule, are striated. The circulatory organs of Arthropoda vary greatly in plan and degree of complication, but there is never a completely closed circulation. « 3 The development of Arthropoda may be accompanied by striking metamorphosis, e.g., in many marine Crustacea, but, as in other animals, the terrestrial and fluviatile forms usually develop directly. Even in Insects, which appear to contradict this rule flatly, the exception is more apparent than real. The Insect emerges from the egg as a fully formed larva, and so far its development is direct. It is the full-grown larva, however, which corresponds most nearly to the adult Myriopod, while the pupa and imago are stages peculiar to the Insect. It is not by any process of embryonic development, but by a secondary metamorphosis of the adult that the Insect acquires the power of flight necessary for the deposit of eggs in a new site. THE COCKROACH 12 — ‘LX = ‘ptoo-oarou {9 "ar $4.xv0y ‘gz Sumgqoor ‘yf youuroys oyTTAYyo “yg £ paezzi3 4 £doro Wo { rioArOSo4 Awearyes Sug: f purps Lxearpes by Ssndvydosa 909 \ ‘suvSio pedroutid ay} Jo uorqztsod oyy Moys 04 ‘OVOIYOOH oyeuray Jo uoroos [PurpnytsuoT—e “Srp ne ITS ZOOLOGICAL POSITION. 13 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 antennz ; and by the tracheal respiration. Myriopods and Arachnida have no distinct thorax. Most Crustacea have two pairs of antenne, while in Arachnida antenne are wanting altogether. Crustacea, if they possess special respiratory organs at all, have branchize (gills) in place of traches (air-tubes). In Arachnida, Myriopoda, and Crustacea there are usually more than three pairs of ambulatory legs in the adult. The appendages of an Insect’s head (antennze, mandibles, maxille) are appropriated to special senses, or to the operations of feeding, and have lost that obvious correspondence with walking legs which they still retain in some lower Arthropoda (Peripatus, Limulus, Arachnida). The thorax consists of three* segments, each of which carries a pair of ambulatory legs. No abdominal legs are found in any adult insect. The middle thoracic segment may carry a pair of wings or wing-covers, and the third segment a pair of wings. The lower or less-specialised Insects, such as the Cockroach, have nearly as many nerve-ganglia as segments, and the longi- tudinal connectives of the nerve-cord are double. In the adult of certain higher Insectst (e.g., many Coleoptera, and some Diptera) the nerve-ganglia are concentrated, reduced in number, and restricted to the head and thorax; while all the con- nectives, except those of the esophageal ring, may be outwardly single. The heart, or dorsal vessel, is subdivided by constrictions into a series of chambers, from which an aorta passes forwards to the head. Air is usually taken into the body by stigmata or breathing- pores,? which lie along the sides of the thorax and abdomen. * In some Insects there are traces of a fourth thoracic segment. + So also in some larve (Calandra, @strus, &c.). + In some aquatic Insects the exchange of gases is effected by ‘‘ pseudobranchiz,” and the tracheal system is closed. 14 THE COCKROACH : It circulates through repeatedly-branching tracheal tubes, whose lining is strengthened by a spiral coil. Air-sacs (dilated por- tions of the air-tubes) occur in Insects of powerful flight. The generative organs are placed near the hinder end of the body.* Most Insects are oviparous.t The sexes are always dis- tinct ; but imperfect females (“neuters”’) occur in some kinds of social Insects. Agamogenesis (reproduction by unfertilised eggs) is not uncommon. 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 and wingless Thysanura. Two orders remain, in which the adult is commonly provided with wings; of these, the Orthoptera have biting jaws, the Hemiptera, jaws adapted for piercing and sucking. The name of Black Beetle, often given to the Cockroach, is therefore technically wrong. True Beetles have a resting or chrysalis stage, and may further be recognised in the adult state by the dense wing-covers, meeting along a straight line down the middle of the back, and by the transversely folded wings. Cockroaches have no resting stage, the wing-covers overlap, and the wings fold up fan-wise. 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 :— * Dragon-flies have the male copulatory apparatus, but not the genital aperture, in the fore part of the abdomen. 7 Aphis and Cecidomyia are at times viviparous, and a viviparous Moth has been observed by Fritz Miiller (Trans. Entom. Soc. Lond., 1883). ITS ZOOLOGICAL POSITION, ] a 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 pronotum. Eyes large, ocelli rudimentary, usually two, antennz long and slender. FF, te, Anal area , “nlernomedian area [24 a a” io” ee sss SSF ye of Pe SSSR Mediastinal area 4.—Generalised sketch of Cockroach wing-cover. About eight hundred species of Cockroaches have been defined, and to facilitate their arrangement, three groups have been proposed, under which the different genera are ranked.* Group 1. Both sexes wingless (Polyzosteria). Group 2. Males winged, females wingless (Perispheria, Heterogamia). Group 3. Both sexes with more or less developed wings (about 7 genera). * For descriptions of the species Fischer’s Orthoptera Europza (1853) or Brunner von}Wattenwyl’s Nouveau Systéme des Blattaires (1865) may be consulted. The classification adopted by the last-named author is here summarised. BLATTARIA. A,.—Femora spinous (Spinose). Fam. 1.—Zctobide. Seventh abdominal sternum undivided in female. Sub- anal styles absent in male. Wings with triangular apical area. Ectobia, including ZL. lapponica (Blatta) and other genera. Fam. 2.—Phyllodromide. Seventh abdominal sternum undivided in female. Sub-anal styles usual in male (0 or rudimentary in Phyllodromia). Wings without triangular apicalarea. Phyllodromia, including P. germanica (Blatta) and other genera. Fam. 3.—Epilampride. Fam. 4.—Periplanetide. Seventh abdominal sternum divided in female. Sub-anal styles conspicuous in male. Polyzosteria, Periplaneta, Kc. B.—Femora not spinous (Mutice). Families.—Chorisoneuride, Panchloride, Perispheride, Corydide, Hetero- gamide, Blaberide, Panesthide. Many useful references will be found in Seudder’s Catalogue of N. American Orthoptera, Smiths. Misc. Coll., viii. (1868). 16 THE COCKROACH. In Group 3 occur the only two genera which we shall find it necessary to describe—viz., Blatta, which includes the European Cockroaches, and Periplaneta, to which belong the Cockroaches of tropical Asia and America. Genus Biatia. A pulvillus between the claws of the feet. The seventh sternum of the abdomen entire in both sexes ; sub-anal styles rudimentary in the male. Genus Periplaneta. Readily distinguished from Blatta by the divided seventh abdominal sternum of the female, and the sub-anal styles of the male. Two species of Periplaneta have been introduced into Europe. These are— 1. P. orientalis (Common Cockroach, Black Beetle). Waing- covers and wings not reaching the end of the abdomen in the male; rudimentary in the female. 2. P.americana (American Cockroach). Waing-covers and wings longer than the body in both sexes. CHAPTER III. Tue Natrurat History or tHE CockROAcu. SPECIAL REFERENCES. HumMen. Essais Entomologiques, No. 1 (1821). CoRNELIUS. Beitriige zur niihern Kenntniss von Periplaneta orientalis (1853. ) GirRARD. La domestication des Blattes. Bull. Soc. d’Acclimatisation, 3° Sér., Tom. IV., p. 296 (1877). Range. Tue common Cockroach is native to tropical Asia,* 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 Blattze as occurring in wine cellars, flour mills, &c., in England. It is hard to determine in all cases of what insects he is speaking, since one of his rude woodcuts of a “ Blatta”’ is plainly Blaps mortisaga; another is, however, recognisable as the female of P. orientalis; a third, more doubtfully, as the male of the same species. He tells how Sir Francis Drake took the ship “ Philip,” + laden with spices, and found a great multitude of winged Blattz on board, ‘‘ which were a little larger, softer, and darker than ours.” Perhaps these belonged to the American species, but the description is obscure. Swammerdam also was acquainted with our Cockroach as an inhabitant of Holland early in the seventeenth century. He speaks of it as “‘insectum * Linnzus was certainly mistaken in his remark (Syst. Nat., 12th ed.) that this species is native to America, and introduced to the East—‘‘ Habitat in America: hospitatur in Oriente.” He adds, ‘‘ Hodie in Russiz adjacentibus regionibus frequens ; incepit nuperis temporibus Holmiz, 1759, uti dudum in Finlandia.” + This must have been the “San Felipe,” a Spanish East Indiaman, taken in 1587. See Motley, United Netherlands, Vol. II., p. 283. Cc 18 THE COCKROACH : illud Indicum, sub nomine Kakkerlak satis notum,” and very properly distinguishes from it “the species of Scarabzus” (Blaps), which Moufet had taken for a Blatta.* The American Cockroach is native to tropical America, but has now become widely spread by commerce. An Australian species also (P. australasie) has begun to extend its native limits, having been observed in Sweden,t Belgium, Madeira, the East and West Indies,t Florida,§ &c. In Florida it is said to be the torment of housekeepers. To the genus Béatta belong a number of small European species, which mostly lurk in woods and thickets. Some of these are found in the south of England. B. /apponica is one of the commonest and most widely distributed. It is smaller than the common Cockroach, and both sexes have long wings and wing-cases. The males are black and the females yellow. It is found on the mountains of Norway and Switzerland as high as shrubs extend, and when sheltered by human dwellings, can endure the extreme cold of the most northern parts of Europe. This is the insect of which Linnzus tells, that in company with Silpha lapponica it has been known to devour in one day the whole stock of dried but unsalted fish of a Lapland village. B. germanica also has the wings and wing-cases well developed in both sexes. Two longitudinal stripes on the pronotum, or first dorsal plate of the thorax, are the readiest mark of this species, which is smaller and lighter in colour than the common Cockroach, It is plentiful in most German towns, and has been introduced from Germany into many other countries;|| but it appears to be native, not to Germany alone, but to Asia and all parts of central and southern Europe. Where and how it first became domesticated we do not know. * Biblia Nature, Vol. I., p. 216. + De Borck. Skandinaviens riitvingade Insekters Nat. Hist., L., i., 35. + Brunner. N. Syst. d. Blattaires, p. 234. § Scudder. Proc. Boston Soc. N.H., Vol. XIX., p. 94. || For example, the Russians often call it Proussaki, the Prussian Cockroach, and believe that.their troops brought it home with them after the Seven Years’ War. The native Russian name is Tarakan. In Finland and Sweden the same species is called Torraka, which appears to be a corruption of the Russian word, and confirms the account of Linnzus quoted above. B. germanica is found in the United States from the Atlantic to the Pacifit. It is generally known as the Croton Bug, because in New York it is often met with about the water pipes, which are supplied from the Croton River (Dr. Scudder). ITS NATURAL HISTORY. 19 The other species of Cockroaches which have been met with in Europe are Panchlora madera, said by Stephens to be occa- sionally seen in London, and Blabera gigantea, the Drummer of the West Indies, which has often been found alive in ships in the London Docks. Blatta germanica, Periplaneta orientalis, and P. americana, are so similar in habits and mode of life as to be interchangeable, and each is known to maintain itself in particular houses or towns within the territory of another species, though usually without spreading. Orientalis is, for example, the common Cockroach of England, but germanica frequently gets a settlement and remains long in the same quarters. H.C. R., in Science-Gossip for 1868, p. 15, speaks of it as swarming in an hotel near Covent Garden, where it can be traced back as far as 1857. In Leeds, one baker’s shop is infested by this species; it is believed to have been brought by soldiers to the barracks, after the Crimean war, and to have been carried to the baker’s in bread-baskets. We have met with no instance in which it has continued to gain ground at the expense of orientalis. Americana also seems well estab- lished in particular houses or districts in England. H.C. R. (loc. cit.) mentions warehouses near the Thames, Red Lion and Bloomsbury Squares, and the Zoological Gardens, Regent’s Park. It frequents one single warehouse in Bradford, and is similarly local in other towns with foreign trade. Many cases are recorded in which germanica has been replaced by orientalis, as in parts of Russia and Western Germany, but detailed and authenticated accounts are still desired. On the whole orientalis seems to be dominant over both germanica and americana. The slow spread of the Cockroaches in Europe is noteworthy, not as exceptional among invading species, but as one more illustration of the length of time requisite for changes of the equilibrium of nature. It took two centuries from the first introduction of orientalis into England for it to spread far from London. Gilbert White, writing, as it would appear, at some date before 1790, speaks of the appearance of “an unusual insect,” which proved to be the Cockroach, at Selborne, and says: “‘ How long they have abounded in England I cannot say; 20 THE COCKROACH : but have never observed them in my house till lately.”* It is probable that many English villages are still clear of the pest. The House Cricket, which the Cockroaches seem destined to supplant, still dwells in our houses, often side by side with its rival, sharing the same warm crannies, and the same food. The other imported species, though there is reason to suppose that they cannot permanently withstand orientalis, are by no means beaten out of the field; they retreat slowly where they retreat at all, and display inferiority chiefly in this, that in countries where both are found, they do not spread, while their competitor does. It may yet require some centuries to settle the petty wars of the Cockroaches. It is also worth notice that in this, as in most other cases, the causes of such dominance over the rest as one species enjoys are very hard to discover. We caunot explain what peculiarities enable Cockroaches to invade ground thoroughly occupied by the House Cricket, an insect of quite similar mode of life: and it is equally hard to account for the superiority of orientalis over the other species. It is neither the largest nor the smallest; it is not perceptibly more prolific, or more voracious, or fonder of warmth, or swifter than its rivals, nor is it easy to see how the one conspicuous structural difference—viz., the rudimentary state of the wings of the female, can greatly favour orientalis. Some slight advantage seems to lie in characteristics too subtle for our detection or comprehension. Food and Habits. As to the food of Cockroaches, we can hardly except any animal or vegetable substance from the long list of their depre- dations. 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 please. They are extremely fond of warmth, lurking in nooks near the * Bell’s Edition, Vol. I., p. 454. - ITS NATURAL HISTORY. 3] oven, and abounding in bakehouses, distilleries, and all kinds of factories which provide a steady heat together with a supply of something eatable. Cold is the only check, and an unwarmed room during an English winter is more than they can endure. They are strictly nocturnal, and shun the light, although when long unmolested’ they become bolder. The flattened body enables the Cockroach to creep into very narrow crevices, and during cold weather it takes refuge beneath the flags of a kitchen floor, or in other very confined spaces. The Cockroach belongs to a miscellaneous group of animals, which may be described as in various degrees parasitic upon men. These are all in a vague sense domestic species, but have not, like the ox, sheep, goat, or pig, been forcibly reduced to servitude; they have rather attached themselves to man in various degrees of intimacy. The dog has slowly won his place as our companion; the cat is tolerated and even caressed, but her attachment is to the dwelling and not to us; the jackal and rat are scavengers and thieves; the weasel, jackdaw, and magpie are wild species which show a slight preference for the neigh- bourhood of man. All of these, except the cat, which holds a very peculiar place, possess in a considerable degree qualities which bring success in the great competitive examination. They are not eminently specialised, their diet is mixed, their range as natural species is wide. Apart from man, they would have become numerous and strong, but those qualities which fit them so well to shift for themselves, have had full play in the dwellings of a wealthy and careless host. Of these domestic parasites at least two are insects, the House-fly and the Cock- roach; and the Cockroach in particular is eminent in its peculiar sphere of activity. The successful competition of Cockroaches with other insects under natural conditions is sufficiently proved by the fact that about nine hundred species have already been described,* while their rapid multiplication and almost world- wide dissemination in the dwellings of man is an equally striking proof of their versatility and readiness to adapt them- selves to artificial circumstances. In numerical frequency they * British Museum Catalogue of Blattarie (1868) and Supplement (1869). It is probable that the number is over-estimated in this catalogue, the same species being occasionally renamed. 22 THE COCKROACH: probably exceed all domestic animals of larger size, while in geographical range the five species, Japponica, germanica, orientalis, americana, and australasie, are together comparable to the dog or pig, which have been multiplied and transported by man for his own purposes, and which cover the habitable globe. 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 Cock- roaches 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 abdomen, and the unconcentrated nervous system, are marks of the most primitive insect-types. The order Orthoptera is un- deniably the least specialised among winged insects at least, and within this order none are more simple in structure, or reach farther back in the geological record than the Cockroaches. The wingless Thysanura are even more generalised, but their geological history is illegible.* - 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 of the vulva is formed, which is hollow, and opens forwards towards the outlet of the common oviduct. Eggs are * Brongniart has just described a Carboniferous Insect which he considers a Thysanuran (Dasyleptus Lucasi), though it has but one anal appendage. See C. R. Soc. Ent., France, 1885. P | ITS NATURAL HISTORY. 23 now passed one by one into the capsule ; and as it becomes full, its length is gradually increased by fresh additions, while the first-formed portion begins to protrude from the body of the female. When sixteen eggs have descended, the capsule is closed in front, and after an interval of seven or eight days, is dropped in a warm and sheltered crevice. In Periplaneta orientalis it measures about *45 in. by *25 in. (fig. 5). The ova Ls ml tl mt il )» Hy Wh mn IN iM it sili I Fig. 5.—Egg-capsule of P. orientalis (magnified). A, external view ; B, opened ; C, end view. develop within the capsule, and when ready to escape are of elongate-oval shape, resembling mummies in their wrappings. Eight embryos in one row face eight others on the opposite side, being alternated for close packing. Their ventral surfaces, which are afterwards turned towards the ground, are opposed, and their rounded dorsal surfaces are turned towards the wall of capsule; their heads are all directed towards the serrated edge. The ripe embryos are said by Westwood to discharge a fluid (saliva?) which softens the cement along the dorsal edge, and enables them to escape from their prison. In Blatta germanica the female is believed to help in the process of extrication.* The larvee are at first white, with black eyes, but soon darken. They run about with great activity, feeding upon any starchy food which they can find. The larve of the Cockroach hardly differ outwardly from the adult, except in the absence of wings. The tenth tergum is notched in both sexes, as in the adult female. The sub-anal styles of the male are developed in the larva. Cornelius, in his Beitraége zur nihern Kenntniss von Peri- planeta orientalis (1853), gives the following account of the moults * Hummel, loc. cit. 24 THE COCKROACH : of the Cockroach. The first change of skin occurs immediately after escape from the egg-capsule, the second four weeks later, the third at the end of the first year, and each succeeding moult after a year’s interval. At the sixth moult the insect becomes a pupa,* and at the seventh (being now four years old) it assumes the form of the perfect Insect. The changes of skin Fig. 6.— Young nymph (male). x 6. are annual, and like fertilisation and oviposition, take place in the summer months only. He tells us further that the ova require about a year for their development. These statements are partly based upon observation of captive Cockroaches, and are the only ones accessible; but they require confirmation by independent observers, especially as they altogether differ from Hummel’s account of the life-history of Blatta germanica, and are at variance with the popular belief that new generations of the Cockroach are produced with great rapidity. The antennze of the male nymph resemble those of the adult female. Wings and wing-covers appear first in the later larval * The use of the term pupa to denote the last stage before the complete assump- tion of wings in the Cockroach, is liable to mislead. There is no resting-stage at all; wings are developed gradually, and are nearly as conspicuous in the last larval state as in the so-called pupa. There seems no reason for speaking of pupz in this case. It is preferable to designate as ‘‘nymphs” young and active Insects, immature sexually, but with mouth-parts like those of the adult. See Lubbock, Linn. Trans., 1863, and Eaton, Linn. Trans., 1883. ITS NATURAL HISTORY. 95 stages, but are then rudimentary, and constitute a mere pro- longation of the margins of the thoracic rings. Cornelius says that the round white spot internal to the antenna first appears plainly in the pupa, but we have readily found it in a very young larva. The Insect is active in all its stages, and is Fig. 7.— Older nymph (male) with rudiments of wings. X 23. therefore, with other Orthoptera, described as undergoing “incomplete metamorphosis.” After each moult it is for a few hours nearly pure white. Of the duration of life in this species we have no certain information, and there is great difficulty in procuring any. 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 :— 26 THE COCKROACH: Female. Antenna shorter than the body, the third joint longer than the second. Wings and wing-covers rudi- mentary. Mesosternum divided. Abdomen broader. Terga 8 and 9 not externally visible. The 10th tergum notched. The 7th sternum divided be- hind. The external outlet of the rectum and vulva between the 10th tergum and the 7th sternum. No sub-anal styles. Male. Antenna rather longer than the body, the third joint about as long as the second. Wings and wing-covers well developed. Mesosternum entire. Abdomen narrower. Terga8and9 externally visible. The 10th notched. The 7th sternum undivided. tergum hardly The outlet between the 10th tergum and the 9th sternum. Sub-anal styles. Parasites. We have before us a long list of parasites* which infest the Cockroach. There is a conferva, an ameeba, 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, chameleons, frogs, and wasps, but no single friend, unless those are reckoned as friends which are the foes of its foes. 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 * See Appendix. es to ~“ ITS NATURAL HISTORY. cock and roach, but has really nothing to do with either. The lexicographers usually hold their peace about it, or give deriva- tions which are absurd. Mr. James M. Miall informs us that “Cockroach can be traced to the Spanish cucardcha, a diminutive form of euco or coco (Lat. éoccum, a berry). Cucardcha is used also of the woodlouse, which, when rolled up, resembles a berry. The termination -dcha (Ital. -uccio, -accia) signifies mean or contemptible. The Spanish word has also taken a French form ; at least cogueraches has some currency (see, for example, Tylor’s Anahuace, p. 325). In provincial English Black Clock is a com- mon name. The German word Schabe, often turned into Schwabe, means perhaps Suabian, as Moufet, quoting Cordus, seems to explain.* yranzose and Dédne are other German words for the insect, applied specially to Blatta germanica; and all seem to imply some popular theory as to the native country of the Cockroach.t This etymology of Schabe is not free from suspicion, particularly as the same term is commonly applied to the clothes-moth. Aakerlac, much used in France and French- speaking colonies, is a Dutch word of unknown signification. P. Americana is usually named Kakerlac or Cancrelat by the French; while orientalis has many names, such as Cafard, Ravet, and Béte noire.t The name Blatta was applied by the ancients to quite different insects, of which Virgil and Pliny make mention; Periplaneta is a modern generic term, coined by Burmeister. 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. *Tnsectorum Theatrum, p. 138. The name Schwabe is frequent in Franconia, where it is believed to have taken origin. Suabia adjoins Franconia, to the south. + Compare the Swedish name (supra, p. 18). +A fuller list of vernacular names is given by Rolland, Faune Populaire de la France, Vol. III., p. 285. See also Nennich, Polyglotten Lexicon, Vol. I., p. 620. CHAPTER IV. THe Ovrer SKELETON. SPECIAL REFERENCES. KRUKENBERG. Vergleichend-Physiologische Vortrige. IV.—Vergl. Physiologie der Thierischen Geriistsubstanzen. (1885.) [Chemical Relations of Chitin. ] GRABER. Ueber eine Art fibrilloiden Bindegewebes der Insectenhaut. Arch. f. mikr. Anat. Bd. X. (1874.) [Minute Structure of Integument.] Also, VIALLANES. Recherches sur |’Histologie des Insectes. Ann. Sci. Nat., Zool. VIe Série, Tom. XIV. (1882). AUDOUIN. Recherches anatomiques sur le thorax des Insectes, &c. Ann. Sci. Nat. Tom. I. (1824.) [Theoretical Composition of Insect Segments.] Also, Mitne-Epwarps. Lecons sur la Physiologie et Anatomie Comparée. Tom. X. (1874.) | Savieny. Mémoires sur Jes animaux sans vertébres. Partie I* Théorie des organes de la bouche des Crustacées et des Insectes. (1816.) [Comparative Anatomy of the Mouth-parts.] MuurR. Ueber die Mundtheile der Orthopteren. Prag. 1877. [Mouth-parts of Orthoptera. ] Chitin. WHEN the skin of an Insect is boiled successively in acids, alkalies, aleohol, and ether, an insoluble residue known as Chitin (Cy; Hx N2 Oo) is obtained. It may be recognised and sufficiently separated by its resistance to boiling liquor potasse. 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 fre- quently exhibits is not due to any essential ingredient; it may be diminished or even destroyed by various bleaching processes. The colouring-matter of the chitin of the Cockroach, which is amber-yellow in thin sheets and blackish-brown in dense masses, is particularly stable and difficult of removal. Its com- position does not appear to have been ascertained ; it is white when first secreted, but darkens on exposure to air. Fresh-— THE COCKROACH: ITS OUTER SKELETON, 29 moulted Cockroaches are white, but gradually darken in three or four hours. Lowne* observes that in the Blow-fly the pig- ment is “first to be met with in the fat-bodies of the larvae. These are perfectly white, but when cut from the larva, and exposed to the air, they rapidly assume an inky blackness. When the perfect insect emerges from the pupa, and respiration again commences, the integument is nearly white, or a faint ashy colour prevails. This soon gives place to the characteristic blue or violet tint, first immediately around those portions most largely supplied with air vessels.” Professor Moseley} tells us that, thinking it just within the limits of possibility that the brown coloration of the Cockroach might be due to the presence of silver, he analysed one pound weight of Blatta. He found no silver, but plenty of iron, and a remark- able quantity of manganese. That light has some action upon the colouring matter seems to be indicated by the fact that in a newly-moulted Cockroach the dorsal surface darkens first. Chitin is not peculiar to Insects, nor even to Arthropoda. The pen of cuttle-fishes and the shell of Lingula contain the same substance,t which is also proved, or suspected, to occur in many other animals. The chemical stability of chitin is so remarkable that we might well expect it to accumulate like the inorganic con- stituents of animal skeletons, and form permanent deposits. Schlossberger§ has, however, shown that it changes slowly ~ under the action of water. Chitin kept for a year under water partially dissolved, turned into a slimy mass, and gave off a peculiar smell. This looks as if it were liable to putrefaction. The minute proportion of nitrogen in its composition may explain the complete disappearance of chitin in nature. The Chitinous Cuticle. The chitinous exoskeleton is rather an exudation than a true tissue. It is not made up of cells, but of many superposed * Anatomy of the Blow-fly, p. 11. + Q. J. Mier. Sci., 1871, p. 394. + Krukenberg. Vergl. Physiologische Vortriige, p. 200. Halliburton, Q. J. Micr. Sci., 1885, p. 173. § Ann. d. Chem, u. Pharm., Bd. 98. 30 THE COCKROACH : lamin, secreted by an underlying epithelium, or “ chitino- genous 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 with a high power Fig. 8.—Diagram of Insect integument, in section. &m, basement membrane ; hyp, hypodermis, or chitinogenous layer ; ct, ct’, chitinous cuticle ; s, a seta. shows extremely close and fine lines perpendicular to the laminz. The cells commonly form a mosaic pattern, as if altered in shape by mutual pressure. The free surface of the integument of the Cockroach is divided into polygonal, raised spaces. Here and there an unusually long, flask-shaped, epithelial cell projects through the cuticle, and forms for itself an elongate chitinous sheath, commonly articulated at the base; such hollow sheaths form the hairs or sete of Insects—structures quite different histologically from the hairs of Vertebrates. The polygonal areas of the cuticle correspond each to a chitinogenous cell. Larger areas, around which the surrounding ones are radiately grouped, are discerned at intervals, and these carry hairs, or give attachment to muscular fibres. Viallanes (loc. cit.) has added some interesting details to what was previously known of Insect-hairs. There are, he points out, two kinds of hairs, distinguished by their size and struc- ture. The smaller spring from the boundary between contiguous polygonal areas, and have no sensory character. The larger ones occupy unusually large areas, surmount chitinogenous cells of corresponding size, and receive a special nervous supply. ITS OUTER SKELETON. 31 The nerve* expands at the base of the hair into a spindle- shaped, nucleated mass (bipolar ganglion-cell), from which issues a filament which traverses the axis of the hair, piercing the chitinogenous cell, whose protoplasm surrounds it with a sheath which is continued to the tip of the hair. Such sensory hairs are abundant in parts which are endowed with special sensibility. Fig. 9.—Nerve-ending in skin of Stratiomys larva. h, hairs; 0, their chitinous base; c, nucleus of generating cell; g, ganglion cell. x 250. Copied from Viallanes. Fig. 10.—Diagram of sensory hair of Insect. Cc, chitinous cuticle; h, hair ; ¢, its generating cell; g, ganglion cell; bm, basement-membrane. The chitinous cuticle is often folded in so as to form a deep pit, which, looked at from the inside of the body, resembles a lever, or a hook. Such inward-directed processes serve chiefly for the attachment of muscles, and are termed apodemes (apode- mata). A simple example is afforded by the two glove-tips which lie in the middle line of the under-surface of the thorax (p. 58, and fig. 27). In other cases the pit is closed from the * Previously observed by Leydig in Corethra. By THE COCKROACH: first, and the apodeme is formed in the midst of a group of chitinogenous cells distant from the superficial layer, though continuous therewith. Many tendons of insertion are formed in this way. The two forked processes in the floor of the thorax (p. 58, and fig. 27) are unusually large and complex structures of the same kind. In the tentorium of the head (p. 39, and fig. 17) a pair of apodemes are supposed to unite and form an extensive platform which supports the brain and gullet. Fig. 11.—Nymph (in last larval stage) escaping from old skin. X 23. . Like other Arthropoda, Insects shed their chitinous cuticle from time to time. A new cuticle, at first soft and colourless, is previously secreted, and from it the old one gradually becomes detached. The sete probably serve the same purpose as the “casting-hairs” described by Braun in the crayfish, and by Cartier in certain reptiles,* that is, they mechanically loosen the old skin by pushing beneath it. In many soft-bodied nymphs the new skin can be gathered up into a multitude of fine wrinkles, which facilitate separation, but we have not found such wrinkles in the Cockroach, except in the wings. The integument about to be shed splits along the back of the Cockroach, from the head to the end of the thorax,+ and the animal draws its limbs out of their discarded sheaths with much effort. It is remarkable that the long, tapering, and many- jointed antennz are drawn out from an entire sheath. At the * A condensed and popular account of these researches will be found in Semper’s Animal Life, p. 20. + Prof. Huxley (Anat. Invert. Animals, p. 419) states that the integument splits along the abdomen also, but this is a mistake. ITS OUTER SKELETON. 33 same time the chitinous lining of the tracheal tubes is cast, while that of the alimentary canal is broken up and passed through the body. Fig. 12.—Cast skin of older nymph (‘‘pupa”). X 23. Prolonged boiling in caustic potash, though it dissolves the viscera, does not disintegrate the exoskeleton. This shows that the segments of the integument are not separate chitinous rings, but thickenings of a continuous chitinous investment. Nevertheless, their constancy in position and their conformity in structure often enable us to trace homologies between different segments and different species as certainly as between corres- ponding elements of the osseous vertebrate skeleton. Parts of a Somite. Audouin’s laborious researches into the exoskeleton of Insects* resulted in a nomenclature which has been generally adopted. He divides each somite (segment) into eight pieces, grouped in ~ pairs—viz., terga (dorsal plates), sferna (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 single * Audouin. Rech. anat. sur le thorax des Insectes, &c. (Ann. Sci. Nat., Tom L, p. 97. 1824.) D 34 THE COCKROACH: larval or adult Arthropod. Lower forms and younger stages take us further from such a type, instead of nearer to it; and Audouin’s theoretical conception is most fully realised in the thorax of an adult Insect with well-developed legs and wings. The morphologist would derive all the varieties of Arthropod segments from the very simple and uniform chitinous cuticle found in Annelids and many Insect-larve. This becomes differentiated by unequal thickening and folding in, and a series of rings connected by flexible membranes is produced. Loco- motive and respiratory activity commonly lead to the definition of terga and sterna, which are similarly attached to each other by flexible membranes. A pair of limbs may next be inserted between the terga and sterna, and the simple segment thus composed occurs so extensively in the less modified regions and in early stages that it may well be considered the typical Arthropod somite. Special needs may lead to the division of the sterna into lateral halves, but this is purely an adaptive change. The third thoracic sternum of the male Cockroach, and the second and third of the female are thus divided, as is also the hinder part of the seventh abdominal sternum of the female. In an early stage every somite has its tergal region divided into lateral halves, owing to the late completion of the body on this side. Traces of this division may survive even in the imago. There is often a conspicuous dorsal groove in the thoracic terga, and at the time of moult the terga split along an accurately median line (see fig. 12). Additional pieces may be developed between the terga and sterna, and these have long been termed p/eural.* There may be, for example, single stigmatic plates, as in the abdomen of the Cockroach, pieces to support the thoracic legs, and pieces to support the wings; but the number and position of these plates depends upon their immediate use, and their homologies become very uncertain when Insects of different orders are compared. In general, the pleural elements of the segment are late in development, variable, and highly adaptive. * This application of the word to denote parts intermediate between terga and sterna has become general since its adoption by Audouin. It appears also in the older and deservedly obsolete nomenclature of Kirby and Spence. Professor Huxley has unfortunately disturbed the consistent use of this term by giving the name pleura to the free edges of the terga in Crustacea, ITS OUTER SKELETON, 35 Somites of the Cockroach. The exoskeleton of the Cockroach is divisible into about seventeen segments, which are grouped into three regions, as follows :— Head | Procephalic lobes Post-oral segments int cores vs: we = pe ey Abdomen ... whe sie sie pal 17 It is a strong argument in favour of this estimate that many Insects, at the time when segmentation first appears, possess seventeen segments.t The procephalic lobes, from which a great part of the head, including the antenne, is developed, are often counted as an additional segment. The limbs, which in less specialised Arthropoda are carried with great regularity on every segment of the body, are greatly reduced in Insects. Those borne by the head are converted into sensory and masticatory organs; those on the abdomen are either totally suppressed, or extremely modified, and only the thoracic limks remain capable of aiding in locomotion. ° The primitive structure of the Arthropod limb is adapted to locomotion in water, and persists, with little modification, in most Crustacea. Here we find in most of the appendages§ a basal stalk (protopodite), often two-jointed, an inner terminal branch (endopodite), and an outer terminal branch (exopodite), each of the latter commonly consisting of several joints. It does not appear that the appendages of Insects conform to the biramous Crustacean type, though the ends of the maxillx are often divided into an outer and an inner portion. We shall now proceed to describe, in some detail, the regions of the body of the adult Cockroach. * Where the thorax apparently consists of four somites, as in some Hymenoptera, Hemiptera, Coleoptera, and Lepidotera, the first abdominal segment has become blended with it. + Balfour. Embryology, Vol. I., p. 337. _ $ £.9., by Graber. Insekten, Vol. IL., p. 423. § See, for example, Huxley on the Crayfish. 36 THE COCKROACH: Head; Central Parts. 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 Fig. 13.—Front of Head. x 10. 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, by which the head com- municates with the thorax. A rather long neck allows the head to be retracted beneath the pronotum (first dorsal shield of the thorax) or protruded beyond it. On the front of the head we observe the clypeus, which occupies a large central tract, extending almost completely across the widest part of the face. It is divided above by a sharply bent suture from the two epicranial plates, which form the top of the head as well as a great part of its back and sides. The labrum hangs like a flap from its lower edge. A little above the articulation of the labrum the width of the clypeus is suddenly reduced, as if a squarish piece had been cut out of each lower corner. In the re-entrant angle so formed, the ginglymus, or anterior articulation of the mandible, is situated. The labrum is narrower than the clypeus, and of squarish shape, the lower angles being rounded. It hangs downwards, ITS OUTER SKELETON. 37 with a slight inclination backwards towards the mouth, whose front wall it forms. On each side, about halfway between the lateral margin and the middle line, the posterior surface of the labrum is strengthened by a vertical chitinous slip set with large sete. Each of these plates passes above into a ring, from the upper and outer part of which a short lever passes upwards, and gives attachment to a muscle (/evator menti). Fig. 14.—Top of Head. ep, epicranial plate; oc, eye; ge, gena. X10. The top and back of the head are defended by the two epicranial plates, which meet along the middle line, but diverge widely as they descend upon the posterior surface, thus enclosing a large opening, the occipital foramen. Beyond the foramen, they pass still further downwards, their inner edges receding in a sharp curve from the vertical line, and end below in cavities for the articulation of the mandibular condyles.* p< +e Fig. 15.—Side of Head. oc, eye; ge, gena; mn, mandible. x 10. * One of the few points in which we have to differ from the admirable description of the Cockroach given in Huxley’s Comparative Anatomy of Invertebrated Animals, relates to the articulation of the mandible, which is there said to be earried by the gena. 38 THE COCKROACH : The sides of the head are completed by the eyes and the gene. The large compound eye is bounded above by the epicranium; in front by a narrow band which connects the epicranium with the clypeus; behind, by the gena. The gena passes downwards between the eye and the epicranial plate, then curves forwards beneath the eye, and just appears upon the front of the face, being loosely connected at this point with the clypeus. Its lower edge overlaps the base of the mandible, and encloses the extensor mandibule. The occipital foramen has the form of an heraldic shield. Its lateral margin is strengthened by a rim continuous with the tentorium, or internal skeleton of the head. Below, the fora- men is completed by the upper edge of the tentorial plate, Fig. 16.—Back of Head. ca, cardo ; st, stipes; ga, galea; la, lacinia; pa, palp ; sm, submentum ; m, mentum; pg, paraglossa. » 10. which nearly coincides with the upper edge of the submentum (basal piece of the second pair of maxille) ; a cleft, however, divides the two, through which nerve-commissures pass from the sub-cesophageal to the first thoracic ganglion. Through the occipital foramen pass the cesophagus, the salivary ducts, the aorta, and the tracheal tubes for the supply of air to the head. The internal skeleton of the head consists of a nearly trans- parent chitinous septum, named ¢entorium by Burmeister, which extends downwards and forwards from the lower border of the I'S OUTER SKELETON. 39 occipital foramen. In front it gives off two long crura, or props, which pass to the ginglymus, and are reflected thence upon the inner surface of the clypeus, ascending as high as the antennary socket, round which they form a kind of rim. Each crus is twisted, so that the front surface becomes first internal and then posterior as it passes towards the clypeus. The form of the tentorium is in other respects readily understood from Fig. 17.—Fore-half of Head, with tentorium, seen from behind. x 12. the figure (fig. 17). Its lower surface is strengthened by a median keel which gives attachment to muscles. The esophagus passes upwards between its anterior crura, the long flexor of the mandible lies on each side of the central plate; the supra- cesophageal ganglion rests on the plate above, and the sub- cesophageal ganglion lies below it, the nerve-cords which unite the two passing through the circular aperture. A similar internal chitinous skeleton occurs in the heads of other Orthop- tera, as well as in Neuroptera and Lepidoptera. Palmén* thinks that it represents a pair of stigmata or spiracles, which have thus become modified for muscular attachment, their respiratory function being wholly lost. In Ephemera he finds that the tentorium breaks across the middle when the skin is changed, ‘and each half is drawn out from the head like the chitinous lining of a tracheal tube. * Morphologie des Tracheen-systems, p. 103. 40 THE COCKROACH : Antenne ; Eyes. A pair of antennze 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 Fig. 18.—Base of Antenna of Male (to left) and Female (to right). x 24. about twice as wide as long; from this point they become more elongate. The joints are connected by flexible membranes, and provided with stiff, forward-directed bristles. The ordinary position of the antennze is forwards and outwards. Each antenna is attached to a relatively large socket (fig. 15), which lies between the epicranium and clypeus, to the front and inner side of the compound eyes. A flexible membrane unites the antenna to the margin of the socket, from the lower part of which a chitinous pin projects upwards and supports the basal joint. It is well known that in many Crustacea two pairs of antennze are developed, the foremost pair (antennules) bearing two com- plete filaments. Some writers have suggested that both pairs may be present in Insects, though not simultaneously, the Crustacean antennule being found in the larva, and the Crus- tacean antenna in the adult. This view was supported by the ITS OUTER SKELETON, 4] familiar fact that in many larvie the antenne are placed further forward than in the adult. The three large joints at the base of Orthopterous antenns have been taken to correspond with those of Crustacean antennules, and it has been inferred that in Insects with incomplete metamorphosis, only antennules or larval antenn are developed.* ‘This reasoning was never very cogent, and it has been impaired by further inquiry. Weismann has shown that in Corethra plumicornis, the adult antenna, though inserted much further back than that of the larva, is developed within it,t and Graber has described a still more striking case of the same thing in a White Butterfly.t There is, therefore, no reason to suppose that Insects possess more than one pair of antennze, which is probably preoral, not correspond- ing with either of the Crustacean pairs. We have already noticed (p. 26) the superficial points in which the antenna of the male Cockroach differs from that of the female. The eyes of some Crustacea are carried upon jointed appen- dages, but this is never the case in Insects, though the eye- bearing surface may project from the head, as in Diopsis and Stylops. Professor Huxley§ supposes that the head of an Insect may contain six somites, the eyes representing one pair of appendages. The various positions in which the eyes of Arthro- poda may be developed weakens the argument drawn from the stalk-eyed Crustacea. Claus and Fritz Miller go so far on the other side as to deny the existence of an eye-segment even in Crustacea. 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. * Zaddach, Entw. des Phryganiden Eies, p. 86; Rolleston, Forms of Animal Life, p. 75, &c. + Zeits. f. wiss. Zool., Bd. XVI., pl. vii., fig. 33. + Insekten, Vol. II., p. 508. § Anat. Invert. Animals, p. 398. 42 THE COCKROACH : There are three pairs of jaws, disposed behind the labrum, as in the diagram :— : LaAprum. lst pair of Jaws (MANDIBLEs). 2nd ‘6 (MAXILL#). 3rd e (Laxivum, or 2nd pair of Maxillz). Fig. 19.—Diagram of Cockroach Jaws, in horizontal section. The mandible is undivided in all, or nearly all, Insects. Each maxilla may consist of A palp on the outer side, A galea (hood), A lacinia (blade), on the inner side. The galea (hood) of the 3rd pair of jaws is sometimes called the paraglossa. A tongue-like process may be developed from the front wall of the mouth (epipharynz), or from the back wall (hypopharynx or dingua).* Both epipharynx and hypopharynx project into the mouth, and, in some Diptera, far beyond it. The tip of the labium is sometimes produced into a long tongue, called the igu/a (strap). The mouths of Insects may be classed as :— Brrrvc.—Orthoptera, Neuroptera, Coleoptera (in some Coleoptera a licking tongue is developed), most Hymenoptera. Lickinc AND Suckinc.—Some Hymenoptera—e.g., Honey Bee. Suckine.—(a) With lancets—Diptera, Hemiptera. (b) Without lancets—Lepidoptera. * Pyofessor Huxley has proposed to call the attached base hypopharynx, and the free tip lingua. ITS OUTER SKELETON. 13 The reference of these to a common plan, and the determina- tion of the constituent parts, is mainly the work of Savigny. Mouth-parts were made the basis of the classification of Insects by Fabricius (1745-1808). Fig. 20.—The Jaws, separated. Mn, mandible, seen from behind (to left) and front (to right) ; Ma! maxilla (first pair); Mx! labium, or second pair of maxille. The other letters as before. x 20. 44 THE COCKROACH : The mandibles of the Cockroach are powerful, single-jointed* jaws, each of which is articulated by a convex “condyle” to the lower end of the epicranial plate, and again by a concave ‘“‘ginglymus”’ to the clypeus. The opposable inner edges are armed with strong tooth-like processes of dense chitin, which interlock when the mandibles close; those towards the tip of the mandible are sharp, while others are blunt, as if for erush- ing. Each mandible can be moved through an angle of about 30°. A flexible chitinous flap extends from its inner border to the labrum. The powerful flexor of the mandible arises within the epicranial vault; its fibres converge to a chitinous tendon, which passes outside the central plate of the tentorium, and at a lower level through a fold on the lower border of the clypeus, being finally inserted near the ginglymus. A short flexor arises from the crus of the tentorium. The extensor muscle arises from the side of the head, passes through the fold formed by the lower end of the gena, and is inserted close to the outer side of the condyle of the mandible. The anterior maxille lie behind the mandibles, and like them are unconnected with each other. They retain much more of the primitive structure of a gnathite than the mandibles, in which parts quite distinct in the maxille are condensed or suppressed. The constituent pieces are seen in fig. 20. There is a two-jointed basal piece, consisting of the cardo (ca) and the stipes (st). The cardo is a transverse plate bent upon itself, and enclosing muscles; it is attached to the outward-directed pedicel of the occipital frame, and carries the vertical stipes. To the side and lower end of the stipes is attached the five-jointed palp (pa), a five-jointed limb used in feeding and in exploration, while the lacinia (/a) and galea (ga) are articulated to its extremity. The lacinia is internal and posterior to the galea ; it is broad above, but narrows below to a bifid tooth of dense chitin ; its inner surface is beset with a cluster of strong sete. The galea is more flexible, and forms an irregular three-cornered * Professor J. Wood-Mason points out that in Machilis (one of the Thysanura) the mandible shows signs of segmentation, while the apical portion is deeply divided into an inner and an outer half. Ripe embryos of Panesthia (Blatta) javanica are said to exhibit folds which indicate the consolidation of the mandible out of separate joints, while the cutting and crushing portions of the edge are divided by a ‘‘sutural mark,” which may correspond to the line of junction of the divisions of a biramous appen- dage (Trans. Ent. Soc., 1879, pt. 2, p. 145). ITS OUTER SKELETON. 15 prism with an obliquely truncated end, upon which are many fine hairs. A flexible and nearly transparent flap connects the inner edges of the stipes and cardo, and joins both to the labium. The muscles which move the bases of the maxilla spring from the crura, central plate, and keel of the tentorium. On the posterior surface of the head, below the occipital foramen, we find a long vertical flap, the labium, which extends downwards to the opening of the mouth. It represents a second pair of maxille, fused together in their basal half, but re,aining elsewhere sufficient resemblance to the less «modified smterior pair to permit of the identification of their component parts. The upper edge is applied to the occipital frame, but is neither continuous with that structure nor articulated thereto. By stripping off the labium upwards it may be seen that it is really continuous with the chitinous integument of the neck. The broad shield-like base is incompletely divided by a trans- verse hinge into an upper and larger piece, the submentum, and a distal piece, the mentum. To the mentum are appended representatives of the galeze (here named parag/osse) and laciniz, while a three-jointed palp with an additional basal joint (dis- tinguished as the palpiger) completes the resemblance to the maxille of the first pair.* In front of the labium, and lying in the cavity of the mouth is a chitinous fold of the oral integument, the /ingua, which lies like a tongue in the floor of the mouth. The common duct of the salivary glands enters the lingua, and opens on its hinder surface. The lingua is supported by the chitinous skeleton represented in the figures of the salivary glands. (Chap. vii., infra.) The epipkarynx, which is a prominent part in Coleoptera and Diptera, is not recognisable in Orthoptera. Functions of the Antenne and Mouth-parts. We must now shortly consider the functions of the parts just described. The antenne 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 * The homology of the labium with the first pair of maxillz is in no other Insects so distinct as in the Orthoptera. 46 THE COCKROACH : concerning its immediate surroundings. Long antenne, 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 authors have found reason to suppose that in the Insect- antenna resides the sense of hearing, but no evidence worth the name is forthcoming in favour of this view. Much better support can be found for the belief that the antenna is an olfactory organ,* and some experiments which seem conclusive on this point will be cited in a later chapter. In the Cockroach the mandibles and maxille are the only important instruments of mastication. The labium is indirectly concerned as completing the mouth behind and supporting the lingua, which is possibly of importance in the ordinary opera- tions of feeding. Plateaut+ has carefully described the mode of mastication as observed in a Carabus, and his account seems to hold good of biting Insects in general. The mandibles and maxille act, as he tells us, alternately, one set closing as the others part. The maxille actually push the morsel into the buccal cavity. When the mandibles separate, the head is slightly advanced, so that the whole action has some superficial resemblance to that of a grazing quadruped. The palps of the maxillz and labium have been variously regarded as sensory and masticatory instruments. Not a few authors believe that they are useful in both ways. The question has lately been investigated experimentally by Plateau,t who finds that removal of both maxillary and labial palps does not interfere either with mastication or the choice of food. He observes that in the various Coleoptera and Orthoptera sub- mitted to experiment the palps are passive while food is being passed into the mouth. Plateau’s experiments are conclusive as to the subordinate value of the palps in feeding. The observation of live Cock- * Rosenthal, Ueb. d. Geruchsinn der Insekten. Arch. f. Phys. Reil u. Autenrieth, Bd. X. (1811). Hauser, Zeits. f. wiss. Zool., Bd. XXXIV. (1880). + Mém. Acad. Roy. de Belgique, Tom. XLI. (1874). Prof. Plateau’s writings will often be referred to in these pages. We owe to him the most important researches into the physiology of Invertebrates which have appeared for many years. + Exp. sur le Role des Palpes chez les Arthropodes Maxillés. Pt. I. Bull. Soc. Zool, de France, Tom. X. (1885). ITS OUTER SKELETON, 47 roaches has satisfied us that the palps are constantly used when the Insect is active, whether feeding or not, to explore the surface upon which it moves. We have seen no ground for attributing to the palps special powers of perceiving odours or flavours, nor have we observed that they aid directly in filling the mouth with food. It is worthy of note that Leydig has described and figured in the larva of Jydroporus (?), and Hanser in Dytiscus, Carabus, &c., a peculiar organ, apparently sensory, which is lodged in the maxillary and labial palps. It consists of whitish spots, sometimes visible to the naked eye, characterised by unusual thinness of the chitinous cuticle and by the aggregation beneath it of a crowd of extremely minute sensory rods. Of this organ no satisfactory explanation has yet been given.* 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.t 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 vary extremely. It would be hard to find feeding- organs more unlike, at first sight, than the stylets of a Gnat and the proboscis of a Moth, yet the study of a few well-selected _ types will satisfy the observer that both are capable of deriva- tion from a common plan. Nor is this common plan at all vague. It is accurately pictured in the jaws of the Cockroach and other Orthoptera. These correspond so entirely with the primitive arrangement, inferred by a process of abstraction from * Leydig, Taf. z. vergl. Anat., pl. x., fig. 3. Hauser, Zeits. f. wiss. Zool., Bd. XXXIV., p. 386. Jobert has figured the sensory organs of the maxillary palps of the Mole-cricket (Ann. Sci. Nat., 1872), and Forel similar organs in Ants (Bull. Soe. Vaudoise, 1885). + The reader who desires to follow this subject further is recommended to study chap. vi. of Graber’s Insekten, which we have found very useful. 48 THE COCKROACH: the most dissimilar Insects, as to furnish a strong argument for the descent of all higher Insects from forms not unlike Orthop- tera in the structure of their mouth-parts. Though the jaws of the Cockroach are eminently primitive with respect to those of most other Insects, they are themselves derived from a far simpler arrangement, which is demonstrable in all embryonic Insects. Fig. 21 shows an Aphis within the Mn At ) Gar Fig. 21.—Embryo of Aphis. Copied from Mecznikow, Zeits. f. wiss. Zool., Bd. XVL., taf. xxx., fig. 30. References in text. X 220. ege. The rudiments of the antennz (4/), mandibles (Mn), and maxille (Mz!, Mz’) form simple blunt projections, similar to each other and to the future thoracic legs (Z', L*, LZ’). We see, therefore, that all the appendages of an Insect are similar in an early stage of growth; and we may add that a Centipede, a Scorpion, or a Spider would present very nearly the same appearance in the same stage. A Crustacean in the egg would not resemble an Insect or its own parent so closely.* Aquatic life favours metamorphosis, and most Crustacea do not begin life with their full quota of legs, but acquire them as they are wanted. Paired appendages of perfectly simple form are therefore the first stage through which all Insect-jaws must pass. Our second stage is a little more complex, and not nearly so universal as the first. A caterpillar (fig. 22) has its own special wants, and these are met by the unequal development of its jaws. The mandibles are already as complete as those of the Cockroach, which they * Freshwater Crustacea, however, are sometimes similar to their parents at the time of hatching. ITS OUTER SKELETON. 49 closely resemble, but the maxille are stunted cylinders formed mainly of simple rings, and very like the antennew. They show, however, the beginnings of three processes (palp, galea, and lacinia), which are usually conspicuous in well-developed maxilla. The second pair of maxille (Lm) are coalesced, as usual, and Fig. 22.—Head of larva of Goat Moth, seen from behind. Copied from Lyonnet. form the spinneret. The mouth-parts of the Caterpillar do not therefore in all respects represent a universal stage of develop- ment, but show important adaptive modifications. The man- dibles are rapidly pushed forward, and attain their full development in the larva; the first pair of maxille are tempo- rarily arrested in their growth, and persist for a long time in a condition which Orthopterous embryos quickly pass through ; the maxille of the second pair are not only arrested in their growth, but converted to a special use, which seems to stop all further progress. The labial palps, indeed, which are not at all developed in the caterpillar, survive, and become important parts in the moth; but the greater part of the labium disappears when the time for spinning the coccoon is over. We come next to the Orthopterous mouth, which is well illustrated by the Cockroach. This is retained with little modi- fication in all the biting Insects (Coleoptera and Neuroptera). The mandibles may become long and pointed, as in Staphylinus and other predatory forms; in some larve of strong carnivorous propensities (Ant-lion, Dytiscus,* Chrysopa) they are perforate at * In Dytiscus the mandibles are perforate at the base, and not at the tip. See Burgess in Proc. Bost. Soc. Nat. Hist., Vol. XXI., p. 223. E 50 THE COCKROACH: the tip, and through them the juices of the prey are sucked into the mouth, which has no other opening. The labium undergoes marked adaptive change, without great deviation trom the com- mon plan, in the “mask” of the larva of the Dragon-fly. This well-known implement has a rough likeness, in the arrangement and use of its parts, to a man’s fore-limb. The submentum forms the arm, the mentum the fore-arm. Both these are simple, straight pieces, connected by an elbow-joint. The hand is wider, and carries a pair of opposable claws, the paraglossze. In some Coleoptera the labium is reduced to a stiff spine, while in the Stag-beetle it is flexible and hairy, and foreshadows the licking tongue of the Bee. The maxillz become long and hairy in flower-haunting Beetles, and even the mandibles are flexible and hairy in the Scarabzeus-beetles. Fritz Miller has found a singular resemblance to the proboscis of a Moth in a species of Nemognatha, where the maxillz are transformed into two sharp grooved bristles 12 mm. long, which, when opposed, form a tube, but are incapable of rolling up.* In the Honey Bee (fig. 23) nearly all the mouth-parts of the Cockroach are to be made out, though some are small and others extremely produced in length. The mandibles (Mn) are not much altered, and are still used for biting, as well as for knead- ing wax and other domestic work. The mandibular teeth have proved inconvenient, and are gone. The lacinia of the maxilla (Mz') forms a broad and flexible blade, used for piercing succu- lent tissues, but the galea has disappeared, and there is only a vestige of the maxillary palp (J/rp). In the second pair of maxiliz the palp (Zp) is prominent; its base forms a blade, while the tip is still useful as an organ of touch. The para- glossee (Pa) can be made out, but the laciniz are fused to form the long, hairy tongue. This ends in a spoon-shaped lobe (not unlike the “finger” of an elephant’s trunk), which is used both for licking and for sucking honey. The proboscis of the Bee is therefore more like a case of instruments than a single organ. The mandibles form a strong pair of blunt scissors. The maxille are used for piercing, for stiffening and protecting the base of the tongue, and when * Ein Kifer mit Schmetterlingsriissel, Kosmos, Bd. VJ. We take this reference from Hermann Miiller’s Fertilisation of Flowers. a ne a ITS OUTER SKELETON, 5] closed they form an imperfect tube outside the tongue, which, according to Hermann Miiller, is probably suctorial. The labial palps are protective and sensory. Lastly, the central part, or tongue, is a split tube used for suction ; it is very long, so as to Uf \ iy : (ieee retttt tis tt tt \ —*- Fig. 234.—Diagram of Mouth-parts of Honey Bee. OZ THE COCKROACH : penetrate deep flower-cups, and hairy, so that pollen may stick toit. When the proboscis is not in use it can be slid into the mentum (J/), while it and the mentum together can be drawn out of the way downwards and backwards.* In the singular suctorial mouth of Moths and Butterflies we observe, first of all, the great development of the maxille. Fig. 24.—Mouth-parts of Burnet Moth. Fig. 244.—Diagram of Mouth-parts of Moth. Each forms a half-tube, which can be accurately applied to its fellow, so as to form an efficient siphon. In many species the two halves can be held together by a multitude of minute hooks.t At the base of each maxilla is a rudimentary palp (Mxp). The mandibles (Jn) are also rudimentary and perfectly useless. The labium, which was so important to the larva as a spinneret, has disappeared almost completely, but the labial palps (Zp) are large and evidently important. * An interesting account of the structure and mode of action of the Bee’s tongue is to be found in Hermann Miiller’s Fertilisation of Flowers, where also the evolu- tion of the parts is traced through a series of graduated types. + See Newport’s figure of Vanessa atalanta (Todd’s Cyc., Art. Insecta), or Burgess on the Anatomy of the Milk-weed Butterfly, in Auniversary.Mem. of Boston Soc. Nat. Hist., pl. ii, figs. 8-10 (1880). ' I’TS OUTER SKELETON, 53 In Diptera both piercing and sucking parts are usually present. The Gad-fly (fig. 25) is typical. Here we recognise the labrum (Lr), mandible (Mn), and maxilla (Mz) of the Cockroach transformed into stylets. The maxillary palp (Map) is still sensory. A pointed process, stiffened by chitinous ribs, is developed from the back of the labrum. This is the Mx* Mxp Fig. 25.--Mouth-parts of Gad-fly Fig. 254.—Diagram of Mouth-parts (Tabanus). of Gad-fiy. epipharynx (Zp), a process undeveloped in the Cockroach, though conspicuous in some Coleoptera. All these parts are overtopped by the suctorial labium (Zm), which has a_ two- lobed expansion at the end. In the more specialised Diptera this becomes a kind of cupping-glass. The Gad-fly is inter- mediate between the Gnat, in which all the mouth-parts are converted into piercing organs of extraordinary length and sharpness, and such flies as the House-fly and Blow-fly, where the sucking labium forms an organ of the most elaborate kind, the piercing organs undergoing a marked reduction. Except where the labium is short, it is doubly or trebly hinged, so that it can be readily tucked away under the chin. 54 THE COCKROACH : In Hemiptera the long four-jointed labium (Zm) forms a sheath for the stylets. When not in use the whole apparatus is drawn up beneath the head and prothorax. The mandibles (Mn) are sharp at the tip, and close like a pair of forceps, en- closing the maxillze (Mz). These are of unequal length, only one reaching the end of the mandibular case. Both have saw teeth on the free edge. alps are entirely wanting. Door ET eo Fig. 26.—Mouth-parts of Bug. Copied from Fig. 26A.—Diagram of Mouth-parts Landois, Zeits. f. wiss. Zool., Bd. XVIIL., of Bug. taf, xi., fig. 3. Comparing the four kinds of suctorial mouths, of which the Bee, the Moth, the Fly, and the Bug furnish examples, we observe that. the sucking-tube is formed in the Moth out of the two maxille, in the other three out of the labium. Of these last the Bee has the edges of the labium turned down, so that the siphon becomes ventral; in the Bug and Fly the edges ITS OUTER SKELETON, 5D are turned wp, and the siphon becomes dorsal. The more specialised flies have the simple arrangement of the Bug com- plicated by a system of branching tubes, which are probably a special modification of the salivary duct. Similar as the mouth-parts of the four types may be in regard to their mode of working, they cannot be reduced to any common plan which differs materially from that presented by the jaws of the Cockroach. 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 develop- ment 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.* Each segment is normally provided with a pair of appendages. The foremost segment soon enlarges beyond the rest, and becomes divided by a median groove into two “procephalic lobes.” + Of the appendages the first eight pairs are usually more prominent than the rest, and of different form; those of the eighth segment, which may be altogether inconspicuous, never attain any functional importance. The first four pairs of appendages are budded off from the future head, while the next three pairs form the walking legs, and are carried upon the thoracic segments. All the existing appendages of the fore part of the body are thus accounted for, but the exact mode of formation of the head has not yet been made out. The chief part of its walls, includ- ing the clypeus, the compound eyes, and the epicranial plates, arise from the procephalic lobes, and represent the much altered segment of which the antenne are the appendages. The labrum is a secondary outgrowth from this segment, and, in some cases at least, it originates as a pair of processes which resemble true * Balfour, Embryology, Vol. I., p. 337. + Huxley, Med. Times and Gazette, 1856-7; Linn. Trans., Vol. XXII., p. 221, and pl. 38 (1858). 56 THE COCKROACH : appendages, though it is unlikely that such is their real character. No means at present exist for identifying the terga and sterna of the head, nor have the gena, the occipital frame, and the cervical sclerites (described below) been assigned to their segments.* It is worthy of notice that in the stalk-eyed Crustacea, the head, or what corresponds to the head of Insecta, consists of either five or six somites, taking into account a diversity of opinion with respect to the eyestalks, while only four pairs of appendages can be certainly traced in the head of the Insect. The mandibles and maxillz exist to the same number in both groups, and are homologous organs, so far as is known; the numerical difference relates therefore to the antenne, of which the Crustacean possesses two pairs, the Insect only one. Whether the pair deficient in the Insect is altogether undeveloped, or represented by the pair of prominences which give rise to the labrum,f is a question of much theoretical interest and of not a little difficulty. The following table shows the appendages of the head and thorax in the two classes. The homologies indicated are, how- ever, by no means established.¢ CRAYFISH. | CockROACcH. | Antenne. Eyestalks. Antennules. Antenne. Mandibles. Mandibles. Maxille (1). Maxille (1). Maxille (2). Maxille (2). Maxillipeds (1). Thoracic Legs (1). Maxillipeds (2). Thoracic Legs (2). Maxillipeds (3). Thoracic Legs (3). * ““T think it is probable that these cervical sclerites represent the hindermost of the cephalic somites, while the band with which the maxille are united, and the gen, are all that is left of the sides and roof of the first maxillary and the mandi- bular somites.”—Huxley, Anat. Invert. Animals, p. 403. + Balfour, Embryology, Vol. I., note to p. 337. + J. S. Kingsley in Q. J. Micr. Sci. (1885), has reviewed the homology of Insect, Arachnid, and Crustacean appendages, and comes to conclusions very different from | =s ITS OUTER SKELETON, 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 trans- versely, one behind the other, rather behind the dorsal sclerites, and close behind the submentum. There are two lateral sclerites on each side of the neck (fig. 27), a lower squarish one, which is set diagonally, nearly meeting its fellow across the ventral surface, and an oblong piece, closely adherent to the other, which extends forwards and upwards towards the dorsal side. Thorax. 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 (¢ergum) and a ventral plate (sternum). The sterna are often divided into lateral halves. Of the three terga the first (pronotwm) is the largest ; it has a wide free edge on each side, projects forwards over the neck, and when the head is retracted, covers this also, its semi-circular fore-edge then forming the apparent head-end of the animal. The two succeeding terga are of nearly equal size, and each is much shorter than the pronotum, contrary to the rule in winged Insects.* those hitherto accepted. He classifies the appendages as pre-oral (Insect-antenne) and post-oral, and makes the following comparisons :— HEXAPODA. ACERATA. CRUSTACEA. (=Insecta + Myriopoda?) | (=Arachnida + Limulus.) (1) Antenne. Absent. Absent. (2) Mandibles. Chelicerz. Antennules. (3) Maxillee. Pedipalpi. Antenne. (4) Labium. 1st pair legs. Mandibles. (5) Ist pair legs. 2nd pair legs. 1st Maxille. (6) 2nd pair legs. 3rd pair legs. 2nd Maxille. (7) 3rd pair legs. 4th pair legs. 1st Maxillipeds. Pelseneer (Q. J. Micr. Sci., 1885), concludes that both pairs of antennz are post- oralin A pus, and probably in all other Crustacea. * Many Orthoptera, which seize their prey with the fore legs, have a very long pronotum. 58 THE COCKROACH : All the terga are dense and opaque in the female; in the male the middle one (mesonotum) and the hindmost (metano- tum) are thin and semi-transparent, being ordinarily overlaid by the wing-covers. While the thoracic terga diminish back- wards, the sterna increase in extent and firmness, proportionally to the size of the uttached legs. The prosternum is small and coffin-shaped ; the mesosternum partly divided into lateral halves in the male, and completely so in the female. The metasternum is completely divided in both sexes, while a median piece, carrying the post-furca, intervenes between its lateral halves in the male. Behind the sterna, especially in the =—— (2) x cS chs Fig. 27.—Ventral Plates of Neck and Thorax of Male Cockroach. I, prosternum; II, mesosternum; II], metasternum. X 6. case of the second and third, the flexible under-surface of the thorax is inclined, so as to form a nearly vertical step. In the two hinder of these steps a chitinous prop is fixed; each is Y-shaped, with long, curved arms for muscular attachment, and a central notch, which supports the nerve-cord. The hind- most of these, known as the post-furca, lies immediately behind ITS OUTER SKELETON. 59 the metasternum, and its short basal piece is attached between the lateral halves of that plate. Behind the mesosternum is a somewhat slighter prop, the medi-furca. A third piece of similar nature (the ante-furca), which is well developed in some Insects— e.g., in Ants—is apparently wanting in the Cockroach, though there ‘is a transverse oval plate behind the prosternum, which may be a rudimentary furca. Fig. 27 shows two conical processes which lie in the middle line of the ventral surface of the thorax, one in front of the metasternum, the other in front of the mesosternum. These are the thoracic pits, tubular apodemata, serving for the insertion of muscles. The occurrence of stink-glands in the thorax of Hemiptera,* and of so-called poison-glands in the thorax of Solpuga, led us to look for glands in connection with these processes, but we have found none. Thoracic Appendages. Legs; Wings. 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, Gryllotaipa), and the third pair in leaping Orthoptera (Grasshoppers, &c.), being absent in the cursorial Blattina. Each leg is divided into the five segments usual in Insects (see fig. 28). The coxa is broad and flattened. The trochanter is a small piece obliquely and almost immovably attached to the proximal end of the femur, on its inner side. The femur is nearly straight and narrowed at both ends; along its inner border, in the position occupied by the stridulating apparatus of the hind leg of the Grasshoppers, is a shallow longitudinal groove, fringed by stiff bristles. The tibia is shorter than the femur in the fore leg, of nearly the same length in the middle leg, and longer in the hind leg; it is armed with numerous stiff spines directed towards the free end of the limb. There are usually reckoned five joints in the tarsus, which regularly diminish in length, except that the last joint is as long as the second. All the * Also in Phasmide (see Scudder, Psyche, Vol. I., p. 137). 60 THE COCKROACH : Ila Fig. 28.—The three Thoracic Legs of a Female Cockroach. I, s, sternum}; cx, coxa ; tr, trochanter; fe,femur; tb, tibia; ta, tarsus. In Il[4 the coxa is abducted, and the joints a (episternum) and 3 slightly separated. X 4. ITS OUTER. SKELETON. 6] joints bear numerous fine but stiff hairs upon the walking surface. The extremity of the fifth joint is segmented off, and carries a pair of equal and strongly curved claws.* At the base of each leg are several chitinous plates (fig. 28), upon which no small labour has been bestowed by different anatomists. They are arranged so as to form two joints inter- mediate between the coxa and the sternum, and these two joints admit of a hinge-like movement upon each other, while their other ends are firmly attached to the coxa and sternum respec- tively. (Compare III and IIIa, fig. 28.) These parts in the Cockroach may be taken for two basal leg-joints which have become adherent to the thorax. In other cases, however, they plainly belong to the thorax, and not to the leg. In the Mole- cricket, for instance, similar plates occur; but here they are firmly united, and form the lateral wall of the thorax. In the Locust they become vertical, and lie one in front of the other. Most authors have looked upon them as regular elements of a typical somite. They regard such a segment as including two pleural elements—viz., a dorsal plate (epimeron), and a ventral plate (episternum). We have already (p. 34) given reasons for doubting the constancy of the pieces so named. It is not inconvenient, however, to denote by the term episternum the joint which abuts upon the sternum; for the joint which is applied to the coxa no convenient term exists, and its occurrence in Insects is so partial, that the want need not be supplied at present.t Both joints are incompletely subdivided. In the first thoracic segment of the Cockroach they are less firmly con- nected than in the other two. Cockroaches of both sexes are provided with wings, which, however, are only functional in the male. The wing-covers (or anterior pair of wings) of the male are carried by the second thoracic: segment. As in most Orthoptera genuina, they are denser than the hind wings, and protect them when at rest. They reach to the fifth segment of the abdomen, and one * Professor Huxley (Anat. Invert. Animals, p. 404) points out that the so-called pulvillus ought to be counted as a sixth joint. The same is true of the foot of Diptera and Hymenoptera, where there are six tarsal joints, the last carrying the claws. (Tuffen West on the Foot of the Fly. Linn. Trans., Vol. XXIII.) + The nomenclature adopted by Packard (Third Report of U.S. Entomological Commission) seems to us open to theoretical objections. 62 THE COCKROACH : wing-cover overlaps the other. Branching veins or nervures form a characteristic pattern upon the surface (figs. 4, 29), and it is mainly by means of this pattern that many of the fossil species are identified and distinguished. The true or posterior wings are attached to the metathorax. They are membranous and flexible, but the fore-edge is stiffened, like that of the wing- covers, by additional chitinous deposit. When extended, each wing forms an irregular quadrant of a circle ; when at rest, the radiating furrows of the hinder part close up fan-wise, and the inner half is folded beneath the outer.* The wing reaches back as far as the hinder end of the fourth abdominal segment. The wing-covers of the female are small, and though movable, seem never to be voluntarily extended ; each covers about one-third of the width of the mesonotum, and extends backwards to the Fig. 29.—Wings and Wing-covers of Male Cockroach. x 4. middle of the metanotum. A reticulated pattern on the outer fourth of the metanotum plainly represents the hind wing; it is clearly rather a degeneration or survival than an anticipation of an organ tending towards useful completeness. * On wing-plaiting and wing-folding in Blattariz see Saussure, Etudes sur l’aile des Orthoptéres. Ann. Sci. Nat., Sér. 5° (Zool.), Tom. X. ITS OUTER SKELETON. 63 The rudimentary wing of the female Cockroach illustrates the homology of the wings of Insects with the free edges of thoracic terga, and this correspondence is enforced by the study of the developmént.of the more complete wings and wing-covers of the male. The hinder edges of the terga become produced at the later moults preceding the completely winged stage, and may even assume something of the shape and pattern of true wings ; it is not, however, true, though more than once stated, that winged nymphs are common. Adults with imperfectly developed wings have been mistaken for such. Origin of Insect Wings. The structure of the wing testifies to its origin as a fold of the chitinous integument. [t 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 larvee as those of Ephemeride, Perlide, Phryganide, &. In the larva of Chioeon (Ephemera) dipterum (fig. 30), for example, the second thoracic segment carries a pair of large expansions, which ultimately are replaced by organs of aerial flight. The abdominal segments carry similarly placed respiratory leaflets, the tracheal gills, which by their vigorous flapping movements bring a rush of water against their membranous and tracheated surfaces. Gegenbaur* has argued from the resemblance of these appendages to wings, that the wing and the tracheal leaflet are homologous parts, and this view has been accepted as probable by so competent an observer as Sir John Lubbock.t The leaflets placed most advantageously for propulsion seem to have become exclusively adapted to that end, while the abdominal gills have retained their respiratory character. At the time of change from aquatic to terrestrial life, which takes place in many common Insects when the adult condition is * Grundziige der Vergl. Anat. (Arthropoden, Athmungsorgane. ) 7 Origin and Metamorphoses of Insects, p. 73. THE COCKROACH : 64 x 14. Copied from Vayssiére (loc. cit.). Fig. 30. Chloeon (Chloeopsis) dipterum. Larva in eighth stage, with wings and respiratory leaflets. ITS OUTER SKELETON, 65 assumed, and which, according to Gegenbaur, was a normal event among primitive Insects, the tracheal gill is supposed to disappear, and in its place, at the next moult, an opening, the stigma, is formed by the rupture of an air-tube. Gegenbaur supposes that the primitive Insects were aquatic, and their tracheal system closed. The tracheal gill he takes to be the common structure which has yielded organs so unlike as the wing and the stigma. The zoological rank of the Insects (Kphemeridx, Perlide, and Libellulidie), in which tracheal gills are most usual, is not unfavourable to such an explanation. Lubbock has given reasons for regarding Campodea and the Collembola (of the order Thysanura) as surviving and not very much altered representatives of the most primitive Insects, and he has shown that no great amount of modification would be required to convert the terrestrial Campodea into the aquatic Chlocon- nymph.* We must not forget, however, that tracheal gills are by no means restricted to these families of low grade. Trichoptera, a few Diptera, two Lepidoptera (Vymphula and Acentropus), and two Coleoptera (Gyrinus and Eimis),+ have tracheal gills, and a closed tracheal system in the larval condi- tion. We cannot suppose that these larve of higher orders represent an unbroken succession of aquatic forms, but if we refuse to adopt this alternative, we must admit that the closed tracheal system with tracheal gills may be an adaptive modifi- cation of the open system with stigmata. It is well known¢ that in certain Ephemeride (e.g., Tricorythus and Cenis) a pair of anterior tracheal gills may become trans- formed into large plates, which partly protect the gills behind (fig. 31). A similar modification of the second and third thoracic gills in Prosopistoma and SBetisca brings all the functional respiratory organs under cover, and these enlarged plates resemble stiff and simple wings very closely. * Palmén cites one striking proof of the low position of Ephemeride among Insects. Their reproductive outlets are paired and separate, as in Worms and Crustacea. + These examples are cited by Palmén. } Eaton, Trans. Ent. Soc., 1868, p. 281; Vayssiére, Ann. Sci. Nat., Zool., 1882, p- 91. F 66 THE COCKROACH : q i et on a Hf a‘ fl j ) (| ym \ A i \ i) \ X\, : Al ¥ \ j " \ rl \\ C) 2 A ! iN Ry ] Fig. 31.—Tricorythus. Adult larva, with three functional leaflets. leaflet in front is converted into a protective plate. 7. A, protective plate of Tricorythus larva, seen from the outside. x 26. B, the same from within, showing the attached respiratory appendage. C, protective plate of Coenis larva, without respiratory appendage. All the figures are copied from Vayssiére. The next ITS OUTER SKELETON, 67 Palmén* has subjected Gegenbaur’s hypothesis to a very searching examination. He observes that :— 1. In Campodea, and presumably in other primitive Insects, the tracheal system is not closed and adapted for aquatic respiration, but open. ‘Tracheal gills are not by any means confined to the lowest Insects. (See above, p. 65.) 2. Tracheal gills are not always homodynamous or morpho- logically equivalent. _In Ephemeridz, some are dorsal in position, some ventral (first abdominal pair in Oligoneuria and Rhithrogena); they may be cephalic, springing from the base of the maxilla, as in Oligoneuria and Jolia; Jolia has a branchial tuft at the insertion of each of the fore legs.f In Perlidee the tracheal gills may have a tergal, pleural, sternal, or anal insertion. In some Libellulide also, anal leaflets occur.t 3. Tracheal gills never perfectly agree in position and number with the stigmata throughout the body. Sometimes they occur on different rings, sometimes on different parts of the same ring. Gegenbaur’s statements on this point are incorrect. 4. Tracheal gills may co-exist with stigmata. In Perlide the tracheal gills persist in the imago, and may be found, dry and functionless, beneath the stigmata. In Trichoptera they gradually abort at successive moults, and in some cases remain after the stigmata have opened. | 5. Stigmata do not form by the breaking off of tracheal appendages, but by the enlargement of rudimentary tracheal * Zur Morphologie des Tracheensystems (1577). 7 We take these instances from Eaton, Monograph of Ephemeride, Linn. Trans., 1883, p. 15. +t Charles Brongniart has lately described a fossil Insect from the Coal Measures of Commentry, which he names Corydaloides Scudderi, and refers to the Pseudo- Neuroptera. In this Insect every ring of the abdomen carries laminz, upon which the ramified trachez can still be made out by the naked eye. Stigmata co-existed with these tracheal gills. (Bull. Soc. Sci. Nat. de Rouen, 1885.) Some Crustacea are furnished with respiratory leaflets, curiously like those of Tracheates, with which, however, they have no genetic connection. In Isopod Crustacea the exopodites of the anterior abdominal segments often form opercula, which protect the succeeding limbs. In the terrestrial Isopods, Porcellio and Armadillo, these opercula contain ramified air-tubes, which open externally, and much resemble trachee. The anterior abdominal appendages of ZJ'ylus are provided with air-chambers, each lodging brush-like bundles of air-tubes, which open to the outer air. Lamellz, projecting inwards from the sides of the abdominal segments, incompletely cover in the hinder part of the ventral surface of the abdomen, and protect the modified appendages. (Milne Edwards, Hist. Nat. des Crustacés, Vol. III.) 68 THE COCKROACH : branches, which open into the main longitudinal trunks. In larvae with aquatic respiration these branches exist, though they are not functional. Palmén’s objections must be satisfactorily disposed of before Gegenbaur’s explanation, interesting as it is, can be fully accepted. Palmén has proved, what is on other grounds clear enough, that stigmata are more ancient than tracheal gills, aerial tracheate respiration than aquatic. But there is nothing as yet to contradict the view that the first Insect-wings were adapted for propulsion in water, and that they were respiratory organs before they became motor. It is Gegenbaur’s explana- tion of the origin of stigmata, and not his explanation of the origin of wings, which is refuted by Palmén. Abdomen. In the abdomen of the female Cockroach eight terga (1-7 ; 10) are externally visible. Two more (8, 9) are readily dis- played 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) are externally visible. The first is quite rudimentary, and consists of a transversely oval plate ; the second is irregular and imperfectly chitinised in front ; the seventh is large, and its hinder part, which is boat-shaped, is divided into lateral halves, for facilitating the discharge of the large egg-capsule. In the male Cockroach ten abdominal terga are visible without dissection (fig: 33, p. 70), though the eighth and ninth are greatly overlapped by the seventh. The tenth tergum is hardly notched. Nine abdominal sterna are readily made out, the first being rudimentary, as in the female. The eighth is narrower than the seventh, the ninth still narrower, and largely concealed by the eighth; its covered anterior part is thin and transparent, the exposed part denser. This forms the extreme end of the body, except that the small sub-anal styles project beyond it. The podical plates resemble those of the female. ITS OUTER SKELETON. 69 Pleural elements are developed in the form of narrow stigmatic plates, with the free edge directed backwards. These lie between the terga and sterna, and defend the spiracle.* The modifications of the hindmost abdominal segments will be more fully considered in connection with the reproductive organs. Fig. 32.—Under side of Abdomen of Male and Female Cockroach. x 4. The high number of abdominal segments found in the Cock- roach (ten or eleven) is characteristic of the lower orders of Insecta. It is never exceeded; though in the more specialised orders, such as Lepidoptera and Diptera, it may be reduced to nine, eight, or even seven. The sessile abdomen of the Cock- roach is primitive with respect to the pedunculate abdomen found in such insects as Hymenoptera, where the constricted and flexible waist stands in obvious relation to the operations of stinging and boring, or to peculiar modes of oviposition. The first abdominal segment, which is especially liable to dis- location and alteration in Insects, occupies its theoretical position in the Cockroach, though both tergum and sternum * Gerstaecker has found in the two first abdominal segments of Corydia carunculi- gera (Blattaric) pleural appendages, which are hollow and capable of protrusion. They have no relation to the stigmata, which are present in the same segments, and their function is quite unknown. See Arch. f. Naturg., 1861, p. 107. 70 THE COCKROACH : are reduced in size. The sternum is often altogether wanting, while the tergum may unite with the metathorax. The externally visible appendages of the abdomen are the cerci and the styles of the male Cockroach. The cerci are found in both sexes; they are composed of sixteen rings each, and project beneath the edge of the tenth tergum. They are capable of erection by special muscles, and are supplied by large nerves.* The sub-anal styles are peculiar in their insertion, being carried upon the sternum of their segment (the ninth). Fig. 33.— Profile of Male and Female Cockroach. x 4. The abdominal segments are never furnished with functional legs in adult Insects, but representatives of the lost appendages are often met with in larve. According to Biitschli,t all the abdominal segments are provided with appendages in the embryo of the Bee, though they disappear completely before hatching. Some Hymenopterous larve have as many as eight pairs of abdominal appendages, Lepidopterous larvae at most five (3-6; 10).+ * Jointed cerci are commonly found in Orthoptera (including Pseudo-Neuroptera) ; in the Earwig they become modified and form the forceps. The ‘‘ caudal filaments” of Apus are curiously like cerci. The cerci are concealed in the American Cryptocercus, Scudd. (Fam. Panesthide). + Entw. der Biene. Zeits. f. wiss. Zool. Bd. XX. Or,see Balfour’s Embryology, Vol. I., p. 338. ~ From more recent observations it is probable that abdominal appendages are usually present in the embryos of Orthoptera, Coleoptera, Lepidoptera, and possibly Hymenoptera. The subject is rapidly advancing, and more will be known very shortly. . CHAPTER V. Tue Muscies; tHe Fatr-Bopy anp Ca om. SPECIAL REFERENCES, VIALLANES. Histologie et Développement des Insectes. ‘Ann. Sci. Nat., Zool., Tom. XIV. (1882). KUuHnke in Stricker’s Histology, Vol. I., chap. v. PLATEAU. Various Memoirs in Bull. Acad. Roy. de Belgique (1865, 1866, 1883, 1884). [Relative and Absolute Muscular Force. | Lrypic. Zum feineren Bau der Arthropoden. Miiller’s Archiv., 1855. WEISMANN. Ueber zwei Typen contractilen Gewebes, &c. Zeits. fiir ration. Medicin. Bd. XV. (1862). 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.* Each fibre is invested by a transparent elastic sheath, the sarcolemma, and the space within the sarcolemma is subdivided by trans- verse membranes into a series of compartments. The com- partments are nearly filled by as many contractile discs, broad, doubly refractive plates, which are further divisible into prismatic columns, the sarcous elements, each being as Jong as the contractile disc. Successive sarcous elements, continued from one compartment to another, form the primitive fibrils of the muscle. In cross-section the fibrils appear as polygonal areas bounded by bright lines. Outside the fibres, but within the sarcolemma, are nuclei, imbedded in the protoplasm, or living and formative element of the tissue. * See, for example, Klein’s Elements of Histology, chap. ix. ~I bo THE COCKROACH : The muscular fibres of Insects present some important differences from the fibres just described. The nuclei are often found in the centre, and not on the surface of the fibres in both Insects and Crustacea. In both classes the fibrils are frequently subdivided into longitudinal strands, which have not been distinguished in Vertebrate muscles (Viallanes). The sarco- lemma is often undeveloped. Lastly, Insects, like other Arthropoda, exhibit the remarkable peculiarity that not only their voluntary muscles, but all, or nearly all, the muscles of the body, even those of the digestive tube, are striated.* 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 larvae, 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 and more energetic, the muscles become grouped in a more complicated fashion, and the legs and wings of a flying Insect may be set in motion by a muscular apparatus almost as elaborate as that of a bird. Muscles of the Cockroach. The following short notes on the muscles of the Cockroach, aided by reference to the figures, will render the more note- worthy 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. SrERNAL Muscies oF ABDOMEN.—The Jongitudinal sternal muscles (fig. 34) form a nearly continuous transversely seg- * The exceptions relate chiefly to the alary muscles of the pericardial septum. Lowne (Blow-fiy, p. 5, and pl. v.) states that some of the thoracic muscles of that Insect are not striated. THE MUSCLES; THE FAT-BODY AND CQZLOM, 73 mented sheet, covering the ventral surface between the fore- edge of the second abdominal sternum and the fore-edge of the seventh. These muscles, in conjunction with the longitudinal tergul muscles, tend to telescope the segments. Head muscles- UCL Ot CORA m= — on ve Abd. of coxa Ext. fem. ... 1st tergo-st. Long. stern. Obl. sternal Tergo-stern, ---—------ Fig. 34.—Muscles of Ventral Wall, with the Nerve-cord. x 5. “THE COCKROACH : 74 Head muscles- Lat. thor. ~ Ext. fem. --- Long. terg. - Abd. of coxa -- x ra} ° us) i] o Sad p> wo oS = Tergo-stern. -- Fig. 35.—Muscles of Dorsal Wall, with the Heart and Pericardial Tendons. X 5. THE MUSCLES; THE FAT-BODY AND CCiLOM. 75 The oblique sternal muscles (fig. 34), which are very short, connect the adjacent edges of the sterna (2-3, 3-4, 4-5, 5-6, 6-7). They extend inwards nearly to the middle line, but, like the longitudinal sternal muscles, they are not developed beneath the nerve-cord. Acting together, the oblique sternal muscles would antagonise the longitudinal, but it is probable that they are chiefly used to effect lateral flexion of the abdomen, and that only the muscles of one side of the abdomen contract at once. The tergo-sternal (or expiratory) muscles (figs. 35 and 36) form vertical pairs passing from the outer part of each abdo- minal sternum to the corresponding tergum. ‘Their action is to approximate the dorsal and ventral walls, and thus to reduce the capacity of the abdomen. The first tergo-sternal muscle has its ventral insertion into the stem of the postfurca, and takes an oblique course to the first abdominal tergum. TercaL Muscites or Axspomen.—The Jongitudinal tergal muscles extend from the fore part of each abdominal tergum, including the first, to the same part of the tergum next behind. They are interrupted by longitudinal spaces, so that the muscular sheet is less continuous than on the ventral surface, and has a fenestrated appearance. ‘The direction of the fibres is slightly oblique. Oblique tergal muscles, resembling the oblique muscles of the sterna, are also present. In the thorax the general arrangement of the muscles is greatly modified by the altered form of the dorsal and ventral plates, and by the attachment of powerful limbs. SternaL Muscres or THorax.—Two tubular apodemes, lying one behind the other, project into the thorax from the ventral surface (p. 59 and fig. 27). To the foremost of these are attached three paired muscles and one median muscle. The median muscle passes to the second tubular apodeme. The anterior pair pass forwards and outwards to the base of the prothoracic leg; the next pair directly outwards to the base of the middle leg; while the posterior pair pass outwards and backwards to the arms of the medifurca. From the second tubular apodeme, in front of the metasternum, four pairs of muscles spring. Those of the anterior pass forwards and out- 76 THE COCKROACH : wards to the coxa of the fore limb; the second pair directly outwards to the base of the metathoracic legs; the third pair backwards and outwards to the arms of the postfurca; the fourth pair backwards to the second abdominal sternum. Abd. of coxa Ext. fem. . Fig, 36.—Muscles of lateral wall, &. x 5. The muscles attached to the medi- and postfurca (other than those connecting them with the tubular apodemes) are :— THE MUSCLES; THE FAT-BODY AND CQSLOM. 77 er a Sixt, uy H | erie lt oe, os Retr fairs: Fig. 37.—Muscles of left mesothoracie leg, seen from behind. The muscles are— Adductor and abductor of the coxa; extensor and flexor of femoral joint ; flexor and extensor of tibial joint; flexor of tarsus; and a retractor tarsi, which swings the tarsus backwards, so that it points away from the head. It is opposed by another muscle, which moves the tarsus forwards. Both muscles parallelise the tarsus to the axis of the body, but in opposite directions. 78 THE COCKROACH : (1) A pair passing from the posterior edge of the arms of the medifurca to the stem of the postfurca; (2) a pair which diverge from the stem of the postfurca and proceed to the fore part of the second abdominal sternum; (3) a pair passing from the posterior edge of the arms of the postfurca, these are directed inwards and backwards, and are inserted into the hinder part of the second abdominal sternum ; (4) a pair already mentioned, which correspond in position and action to the tergo-sternal muscles, and spring from the stem of the post- furca, passing upwards and outwards to the sides of the first abdominal tergum. The muscles attached to the arms of each furca pass to other structures in or near the middle line of the body. The pull of such muscles must alter the slope of the two steps in the ventral floor of the thorax (p. 58, and fig. 3, p. 12). When the © furca is drawn forwards, the step is rendered vertical or even inclined forward, the sterna being approximated; while, on the other hand, a backward pull brings the step into a horizontal position, and separates the sterna. TercaL Muscies or THorax.—The longitudinal tergal muscles are much reduced in width when compared with those of the abdomen. Sets of obliquely placed muscles, which may be called the Jateral thoracic muscles, arise from near the middle of each tergum, and converge to tendinous insertions on the fore edge of each succeeding tergum, close to the lateral wall of the body. The principal muscles of the legs are figured and named, and their action can readily be inferred from the names assigned to them. 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-Diirckheim are not a sufficient basis for a thorough treatment of the sub- ject, 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 THE MUSCLES; THE FAT-BODY AND Cd&LoM. 79 of great eminence have been led into erroneous statements when they have attempted to characterise shortly a complex animal mechanism which they did not think it worth while to analyse completely.* The action of flight and the muscles attached to the wings are best studied in Insects of powerful flight. The female Cockroach cannot fly at all, and the male is by no means a good flier. Both sexes are, however, admirably fitted for running. In running, two sets, each consisting of three legs, move simultaneously. A set includes a fore and hind limb of the same side and the opposite middle leg. Numbering them from before backwards, and distinguishing the right and left sides by their initial letters, we can represent the legs which work together as— kh, Ly Rs Ly Ry Ls The different legs have different modes of action. The fore- leg may be compared to a grappling-iron; it is extended, seizes the ground with its claws, and drags the body towards its point of attachment. The middle leg is chiefly used to support and steady the body, but has some pushing power. The hind leg, the largest of the three, is effective in shoving, and chiefly propels the body. 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. * For example, Prof. Huxley, in his Anatomy of Invertebrated Animals (p. 254), says that ‘‘as the hard skeleton [of Arthropods] is hollow, and the muscles are inside it, it follows that the body, or a limb, is bent towards that side of its axis, which is opposite to that on which a contracting muscle is situated.”” The flexor muscles of the tail of the Crayfish, which, according to the above rule, should be extensors, the muscles of the mandibles of an Insect, and the flexors and extensors of Crustacean pincers are among the many conspicuous exceptions to this rule. 80 THE COCKROACH : 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.* The Cockchafer is said to be six times as strong as a horse, making allowance for size. A caterpillar of the Goat Moth, imprisoned beneath a bell-glass, weighing half a pound, which was loaded with a book weighing four pounds, nevertheless raised the glass and made its escape. This interesting subject has been investigated by Plateau,t who devised the following experiment. The Insect to be tested was confined within a narrow horizontal channel, which was laid with cloth. A thread attached to its body was passed over a light pulley, and fastened to a small pan, into which sand was poured until the Insect could no longer raise it. Some of the results are given in the following table :— Table of Relative Muscular Force of Insects (Plateau). Weight of body Ratio of weight lifted in grammes. to weight of body. Carabus auratus... a 0°703 xe 17°4 Nebria brevicollis ... 5 0°046 sie 25°3 Melolontha vulgaris 5s 0-940 ce 14°3 Anomala Frischii ... ie 0°153 po 24°3 Bombus terrestris ... pee 0°381 = 14:9 Apis mellifica ae ons 0-090 Pa 23°5 One obvious result is that within the class of Insects the relative muscular force (as commonly understood) is approxi- mately in the inverse proportion of the weight—that is, the strength of the Insect is (by this mode of calculation) most conspicuous in the smaller species. In a later memoirt Plateau gives examples from different Vertebrate and Invertebrate animals, which lead to the same general conclusion. * Haller. This and other examples are taken from Rennie’s Insect Transformations. + Bull. Acad. Roy. de Belgique, 2° Sér., Tom. xx. (1865), and Tom. xxii. (1866). } Loe. cit. 3° Sér., Tom. vii. (1884). Authorities for the various estimates are cited in the original memoir. THE MUSCLES; THE FAT-BODY AND CdSLOM. 8] Ratio of weight drawn to weight of body (Plateau). Horse Pf bh bad ‘ed ang, AO 46088 Man... sists veg ve ah inal, ieee Meese) ees lake (> tae = ae ONOT. rarer .-. 14°83 to 23°5 The inference commonly drawn from such data is that the muscles of small animals possess a force which greatly exceeds that of large quadrupeds or man, allowance being made for size, and that the explanation of this superior force is to be looked for in some peculiarity of composition or texture. Gerstaecker,* for example, suggests that the higher muscular force of Arthropoda may be due to the tender and yielding nature of their muscles. An explanation so desperate as this may well lead us to inquire whether we have understood the facts aright. Plateau’s figures give us the ratio of the weight drawn or raised to the weight of the animal. This we may, with him, take as a measure of the relative muscular force. In reality, it is a datum of very little physiological value. By general reasoning of a quite simple kind it can be shown that, for muscles possessing the same physical properties, the re/ative muscular force necessarily increases very rapidly as the size of the animal decreases. For the contractile force of muscles of the same kind depends simply upon the number and thickness of the fibres, 7¢, upon the sectional area of the muscles. If the size of the animal and of its muscles be increased according to any uniform scale, the sectional area of a given muscle will increase as the square of any linear dimension. But the weight increases in a higher _ proportion, according to the increase in length, breadth, and depth jointly, or as the cube of any linear dimension.t The * Klassen und Ordnungen des Thierreichs, Bd. V., pp. 61-2. + This change in the relation of weight to strength, according to the size of the structure, has long been familiar to engineers. (See, for example, ‘‘ Comparisons of Similar Structures as to Elasticity, Strength, and Stability,” by Prof. James Thomson, Trans. Inst. Engineers, &c., Scotland, 1876.) The application to animal structures has been made by Herbert Spencer (Principles of Biology, Pt. IT., ch. i.). The principle can be readily explained by models. Place a cubical block upon a square column. Double all the dimensions in a second model, which may be done by fitting together eight cubes like the first, and four columns, also the same as before except in length. Each column, though no stronger than before, has now to bear twice the weight. G 82 THE COCKROACH : ratio of contractile force to weight must therefore become rapidly smaller as the size of the animal increases. Plateau’s second table (see above) actually gives a value for the relative muscular force of the Bee, in comparison with the Horse, which is only one-fourteenth of what it ought to turn out, supposing that both animals were of similar construction, and that the muscular fibres in both were equal in contractile force per unit of sectional area.* A later series of experimentst brings out this difference in a precise form. Plateau has determined by ingenious methods what he calls the Absolute Muscular Forcet of a number of Invertebrate animals (Lamellibranch Mollusca, and Crustacea), comparing them with man and other Vertebrates. His general conclusions may be shortly given as follows:—The absolute muscular force of the muscles closing the pincers of Crabs is * Contractile force varies as sectional area of muscle. Let W be weight of Horse; w, weight of Bee; R, a linear dimension of Horse; 7, a linear dimension of Bee. Then "Contr. force of Horse __ sect. area of muscles (Horse) _ R? Contr. force of Bee ~ sect. area of muscles (Bee) ——r?” : Wo Re: Gea r But since 3 pe ae Theref Contr. force of Horse — Wr eretore ‘Contr. force of Bee ~ wh’ But, by definition, Contr. f. of Horse Rel. m.f. of Horse W Contr. f. of Horse w "Rel. m.f. of Bee ~ Contr. f. of Bee = Contr ie Bevcc ae Ww : Wr wr _ (\ oe De See \Re BA 4 The weight of a horse is about 270,000 grammes, that of a bee 09 gramme ; so that w \4 09 ; (+7) ms (soon) = (-000,000,3)! = ‘0015 (nearly) = Calculated Ratio of \ Relative Muscular Force of Horse to that of Bee. The Observed Ratio (Plateau) is se = ‘02128; so that the relative muscular force of the Horse is more than fourteen times as great in comparison with that of the Bee as it would be if the muscles of both animals were similar in kind, and the proportions of the two animals similar in all respects. + Rech. sur la Force Ahsolue des Muscles des Invertébrés. I® Partie. Mollusques Lamellibranches. Bull. Acad. Roy. de Belgique, 3° Sér., Tom. VI. (1883). Do., Ile Partie. Crustacés Décapodes. Ibid., Tom. VII. (1884). + Statical muscular force and Specific muscular force are synonymous terms in common use. Contractile force per unit of sectional area gives perhaps the clearest idea of what is meant. THE MUSCLES; THE FAT-BODY AND CdLOM, 83 low in comparison with that of Vertebrate muscles. The abso- lute force of the adductor muscles closing a bivalve shell may, in certain Lamellibranchs, equal that of the most powerful Mammalian muscles; in others it falls below that of the least powerful muscles of the frog, which are greatly inferior in contractile force to Mammalian muscles. We find, therefore, that the low contractile force of Insect muscles is in harmony, and not in contrast, with common observation of their physical properties, and that the high vedative muscular force, correctly enough attributed to them, is explicable by considerations which apply equally well to models or other artificial structures. The comparison between the muscular force of Insects and Jarge animals is sometimes made in another way. For example, in Carpenter’s Zoology* the spring of the Cheese-hopper is described, and we are told that “the height of the leap is often from twenty to thirty times the length of the body; exhibiting an energy of motion which is particularly remarkable in the soft larva of an Insect. A Viper, if endowed with similar powers, would throw itself nearly a hundred feet from the ground.” It is here implied that the equation Height of Insect’s leap _ Supposed ht. of Viper’s leap (100 ft.) Length of Insect =~ Length of Viper should hold if the two animals were “endowed with similar powers.” But it is known that the work done by contraction of muscles of the same kind is proportional to the volume of the muscles (“ Borelli’s Law’’),t and. in similar animals the muscular volumes are as the weights. Therefore the equation Work of Insect | Work of Viper Weight of Insect Weight of Viper will more truly represent the imaginary case of equal leaping power. But the work = weight raised x height, and the weight raised is in both cases the weight of the animal itself. Therefore Wt. x Ht. IW Ge se Ett: : we (Insect) = ete | sees (Viper), * Vol. IL., p. 203. The calculation here quoted is based upon an observation of Swammerdam, who relates that a Cheese-hopper, } in. long, leaped out of a box 6 in. deep. + Haughton’s Animal Mechanics, 2nd ed., p. 43. 84 THE COCKROACH : and Ht. (Insect) = Ht. (Viper). The Viper’s efficiency as a leaping animal would, therefore, equal that of a Cheese-hopper if it leaped the same vertical height. Therefore, if the two animals were “endowed with similar powers,” the heights to which they could leap would be equal, and not proportional to their lengths, as is assumed in the passage quoted. Straus-Diirckheim observes that a Flea can leap a foot high, which is 200 times its own length, and this has been considered a stupendous feat. It is really less remarkable than a school- boy’s leap of two feet, for it indicates precisely as great efficiency of muscles and other leaping apparatus as would be implied in a man’s leap to the same height, viz., one foot.* 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 dis- appear, the cell-boundaries become indistinct, and a fluid, loaded with minute refractive granules,t takes the place of the living protoplasm. Rhombohedral or hexagonal crystals, containing uric acid, form in the cells and become plentiful in old tissue. The salt (probably urate of soda) is formed by the waste of the proteids of the body. What becomes of it in the end we do not know for certain, but conjecture that it escapes by the blood which bathes the perivisceral cavity, that it is taken up again by the Malpighian tubules, and is finally discharged into the intestine. The old gorged cells probably burst from time to time, and the infrequency of small cells among them renders it probable that rejuvenescence takes place, the burst cells passing through a resting-stage, accompanied by renewal of their nuclei, and then repeating the cycle of change. The segmental tubes forming the Wolffian body of Verte- brates have at first no outlet, and embryologists have hesitated * In any comparison it is necessary to cite not the height cleared by the man, but the displacement during the leap of his centre of gravity. + The granules are not shown in the figure, having been removed in the prepara- tion of the tissue for microscopic examination. THE MUSCLES; THE FAT-BODY AND CasLOM. 85 to regard this phase of development as the permanent condition of any ancestral form.* It is, therefore, of interest to find in the fat-body of the Cockroach an example of a solid, meso- blastic, excretory organ, functional throughout life, but without efferent duct. Fig. 38.—Fat-body of Cockroach, cleared with turpentine. A, young tissue, with distinct cell-boundaries and nuclei, a few cells towards the centre with dead contents; B, older ditto, loaded with urates, the cell-walls much broken down, and the nuclei gone; tr, tracheal tubes. %X 250. The fat-body is eminently a metabolic tissue, the seat of active chemical change in the materials brought by the blood. Its respiratory needs are attested by the abundant air-tubes which spread through it in all directions. The considerable bulk of the fat-body in the adult Cockroach points to the unusual duration of the perfect Insect. It is usually copious in full-fed larvae, but becomes used up in the pupa-stage. Extensions of the fat-body surround the nervous chain, the reproductive organs and other viscera. Sheets of the same substance lie in the pericardial sinus on each side of the heart. The Celom. The fat-body is in reality, as development shows, the irregular cellular wall of the ccelom, 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 ccelom, the rest of the mesoblast having gone to form the muscular layers of the body-wall and of the digestive tube. * Balfour, Embryology, Vol. II., p. 603. CHAPTER VI. Tue Nervous System AND SENSE ORGANS. SPECIAL REFERENCES. Newport. Nervous System of Sphinx Ligustri. Phil. Trans. (1832-4). Todd’s Cyclopedia, Art. ‘‘ Insecta” (1839). Leyptc. Vom Bau des Thierischen Kérpers. Bd. I. (1864). Tafeln zur. vergl. Anat. Hft. L. (1864). Branpt (E.). Various memoirs on the Nervous System of Insects in Hore Soc. Entom. Ross., Bd. XIV., XV. (1879). MicHEts. Nervensystem von Oryctes nasicornis im Larven—, Puppen—, und Kiferzustande. Zeits. f. wiss. Zool., Bd. XXXIV. (1881). : DietL. Organisation des Arthropodengehirns. Zeits. f. wiss. Zool., Bd, XX VII. (1876). ; : FLOGEL. Bau des Gehirns der verschiedenen Insektenordnungen. Zeits. f. wiss. Zool., Bd. XXX. Sup. (1878). Newton. On the Brain of the Cockroach. Q. J. Micr. Sci. (1879). Journ. Quekett Club (1879). E GRENACHER. Sehorgan der Arthropoden. (1879). [Origin, Structure, and Action of the Compound Eye.] CARRIERE. Sehorgane der Thiere, vergl.-anat. dargestellt (1885). [Comparative Structure of various Simple and Compound Eyes. ] General Anatomy of Nervous Centres. THE. nervous system of the Cockroach comprises ganglia and connectives,* which extend throughout the body. We have, first, a supra-cesophageal ganglion, or brain, a sub-cesophageal ganglion, and connectives which complete the esophageal 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 coalescence or suppression, and we find only eleven ganglia in the Cockroach—viz., two cephalic, three thoracic, and six abdominal. * Yung (‘‘Syst. nerveux des Crustacées Décapodes, Arch. de Zool. exp. et gén.,” Tom. VII.,1878) proposes to name connectives the longitudinal bundles of nerve-fibres which unite the ganglia, and’ to reserve the term commissures for the transverse communicating branches. ee eee THE COCKROACH: ITS NERVOUS SYSTEM. 87 S ae. ony . AQAsz Fig. 39.—Nervous System of Female Cockroach, x 6. a, optic nerve; 6, antennary nerve ; ¢, d, €, nerves to first, second, and third legs; f, to wing-cover; g, to second thoracic spiracle ; h, to wing; 7, abdominal nerve; Jj, to cerci. 88 THE COCKROACH : The nervous centres of the head form a thick, irregular ring, which swells above and below into ganglionic enlargements, and leaves only a small central opening, occupied by the cesophagus. The tentorium separates the brain or supra- cesophageal ganglion from the sub-csophageal, while the connectives traverse its central plate. Since the cesophagus passes above the plate, the investing nervous ring also lies almost wholly above the tentorium. Fig. 40.—Side view of Brain of Cockroach, x 25. op, optic nerve; oe, cesophagus; t, tentorium; sb, sub-cesophageal ganglion; mn, mx, ma’, nerves to mandible and maxille. Copied from E. T. Newton. The brain is small in comparison with the whole head; it consists of two rounded lateral masses or hemispheres, incom- pletely divided by a deep and narrow median fissure. Large optic nerves are given off laterally from the upper part of each hemisphere; lower down, and on the front of the brain, are the ‘two gently rounded antennary lobes, from each of which proceeds an antennary nerve; while from the front and upper part of each hemisphere a small nerve passes to the so-called “ ocellus,’’ a transparent spot lying internal to the antennary ITS NERVOUS SYSTEM AND SENSE ORGANS, 89 socket on each side in the suture between the clypeus and the epicranium. The sub-csophageal ganglion gives off branches to the mandibles, maxilla, und labrum. While, therefore, the supra-cesophageal is largely sensory, the sub-cesophageal gang- lion is the masticatory centre. The csophageal ring is double below, being completed by the connectives and the sub-cesophageal ganglion; also by a smaller transverse commissure, which unites the connectives, and applies itself closely to the under-surface of the cesophagus.* Two long connectives issue from the top of the sub- esophageal ganglion, and pass between the tentorium and the submentum on their way to the neck and thorax. The three thoracic ganglia are large (in correspondence with the important appendages of this part of the body) and united by double connectives. The six abdominal ganglia have also double connectives, which are bent in the male, as if to avoid stretching during forcible elongation of the abdomen. The sixth abdominal ganglion is larger than the rest, and is no doubt a complex, representing several coalesced posterior ganglia; it supplies large branches to the reproductive organs, rectum, and cerci. 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 rela- tively thick, and very distinct neurilemma, probably chitinous, encloses the cord. Its cellular matrix, or chitinogenous layer, * This commissure, which has been erroneously regarded as characteristic of Crustacea, was found by Lyonnet in the larva of Cossus, by Straus-Diirckheim in Locusta and Buprestis, by Blanchard in Dytiscus and Otiorhynchus, by Leydig in Glomeris and Telephorus, by Dietl in Gryllotalpa, and by Liénard in a large number of other Insects and Myriapods, including Periplaneta. See Liénard, ‘‘ Const. de Vanneau cesophagien,” Bull. Acad. Roy. de Belgique, 2° Sér., Tom. XLIX., 1880. 90 THE COCKROACH : is distinguished by the elongate nuclei of its constituent cells.* Tracheal trunks pass to each ganglion, and break up upon and within it into a multitude of fine branches. Fig. 41.—Transverse section of Third Thoracic Ganglion. meu, neurilemmar cells ; ge, ganglionic cells; tr, tracheal tubes; A, ganglionic cells, highly magnified. x-75. 3 Fig. 42.—Longitudinal vertical section of Third Thoracic Ganglion. 7, connective. The other references as in fig. 41. X 75. Bundles of commissural fibres pass from the ganglion cells of one side of the cord to the peripheral nerves of the other. : There are also longitudinal bands which blend to form the connectives, and send bundles into the peripheral nerves. Of : * We have not been able to distinguish in the adult Cockroach the double layer of neurilemmar cells noticed by Leydig and Michels in various Coleoptera. ITS NERVOUS SYSTEM AND SENSE ORGANS. 9] the peripheral fibres, some are believed to pass direct to their place of distribution, while others traverse at least one complete segment and the corresponding ganglion before separating from the cord. 3 i i! ¥ ¥ oe , 2. = = = r ni Fig. 43.— Longitudinal horizontal section of Third Thoracic Ganglion. 2, peripheral nerves. The other references as before. X 75. Many familiar observations show that the ganglia of an Insect possess great physiological independence. ‘The limbs of decapitated Insects, and even isolated segments, provided that they contain uninjured ganglia, exhibit unmistakable signs of life. 92 THE COCKROACH : Median. Nerve-Cord. Lyonnet,* Newport,t and Leydigt 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 commis- sures 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 ganglion it bifurcates, the branches passing outwards and blending with the peripheral nerves. Each branch, close to its origin, swells into a ganglionic enlargement. The median nerve and its branches differ in appearance and texture from ordinary peripheral nerves, being more transparent, delicate, and colourless. They are said to supply the occlusor muscles of the stigmata. In the Cockroach the median nerves are so slightly developed in the thorax and abdomen (if they actually exist) that they are hardly discoverable by ordinary dissection. We have found only obscure and doubtful traces of them, and these only in one part of the abdominal nerve- cord. The stomato-gastric nerves next to be described appear to constitute a peculiar modification of that median nerve-cord which springs from the circum-cesophageal connectives. Stomato-gastric Nerves. In the Cockroach the stomato-gastric nerves found in so many of the higher Invertebrates are conspicuously developed. From the front of each cesophageal connective, a nerve passes forwards upon the cesophagus, outside the chitinous crura of the tentorium. Each nerve sends a branch downwards to the labrum, and the remaining fibres, collected into two bundles, join above the cwesophagus to form a triangular enlargement, the * Traité Anat., p. 201, pl. ix., fig. 1. + Phil. Trans., 1834, p. 401, pl. xvi. + Vom Bau des Thierischen Kérpers, pp. 203, 262; Taf. z. vergl. Anat., pl. vi., fig. 3. Oh a ITS NERVOUS SYSTEM AND SENSE ORGANS. 93 frontal ganglion. From this ganglion a recurrent nerve passes backwards through the esophageal ring, and ends on the dorsal surface of the crop (‘3 inch from the ring), in a triangular oF, Fig. 44.—Stomato-gastric Nerves of Cockroach. fr.g., frontal ganglion; at., anten- nary nerve; conn., connective; pd.g., paired ganglia; 7.7., recurrent nerve; v.g., ventricular ganglion. ganglion, from which a nerve is given off outwards and back- wards on either side. Each nerve bifurcates, and then breaks up into branches which are distributed to the crop and gizzard.* Just behind the esophageal ring, the: recurrent nerve forms a * The stomato-gastric nerves of the Cockroach have been carefully described by Koestler (Zeits. f. wiss. Zool., Bd. XXXIX., p. 592). 94 THE COCKROACH : plexus with a pair of nerves which proceed from the back of the brain. Each nerve forms two ganglia, one behind the other, and each ganglion sends a branch inwards to join the recurrent nerve. Fine branches proceed from the paired nerves of the wsophageal plexus to the salivary glands. The stomato-gastric nerves differ a good deal in different insects; Brandt* considers that the paired and unpaired nerves are complementary to each other, the one being more elaborate, according as the other is less developed. A similar system is found in Mollusca, Crustacea, and some Vermes (e.g., Nemerteans). When highly developed, it contains unpaired: ganglia and nerves, but may be represented only by an indefinite plexus - (earthworm). It always joins the esophageal ring, and sends branches to the cesophagus and fore-part of the alimentary canal. The system has been identified with the sympathetic, and also with the vagus of Vertebrates, but such correlations are hazar- dous; the first, indeed, may be considered as disproved. Internal Structure of Brain. The minute structure of the brain has been investigated by Leydig, Dietl, Flégel, 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 physiological significance, and the homologies of many parts are as yet altogether obscure. The comparative study of new types will, however, in time, bridge over the wide interval between the Insect-brain and the more familiar Verte- brate-brain, which is partially illuminated by physiological experiment. Mr. E. T. Newton has published a clear and useful descriptiont of the internal and external structure of the brain of the Cockroach, which incorporates what had previously been ascertained with the results of his own investigations. He has also described+ an ingenious method of combining a number of successive sections into a dissected model of the * ““Mem. Acad: Petersb.,” 1835. 7 “Q. J. Mier. Sci.,” 1879, pp. 340-356, pl. xv., xvi. + ‘Journ. Quekett Micr. Club,” 1879. ITS NERVOUS SYSTEM AND SENSE ORGANS. 95 brain. Having had the advantage of comparing the model with the original sections, we offer a short abstract of Mr. Newton’s memoir as the best introduction to the subject. He describes the central framework of the Cockroach brain as consisting of two solid and largely fibrous trabecul, which lie side by side along the base of the brain, becoming smaller at their hinder ends; they meet in the middle line, but apparently without fusion or exchange of their fibres. Each trabecula is continued upwards by two fibrous columns, the cauliculus in front, and the peduncle behind; the latter carries a pair of cellular disks, the Fig. 45.—A, lobes of the brain of the Cockroach, seen from within ; c, cauliculus; p, peduncle ; ¢, trabecula. B, ditto, from the front; ocx, outer calyx ; icr, inner calyx. C, ditto, from above. Copied from E. T. Newton. ealices (the cauliculus, though closely applied to the calices, is “not connected with them); these disks resemble two soft cakes pressed together above, and bent one inwards, and the other outwards below. The peduncle divides above, and each branch joins one of the calices of the same hemisphere. This central framework is invested by cortical ganglionic cells, which possess distinct nuclei and nucleoli. A special cellular mass forms a cap to each pair of calices, and this 96 THE COCKROACH : Fig. 46.—Model of Cockroach Brain, constructed from slices of wood representing successive sections. Fig. 47.—Right half of Model-brain seen from the inner side, with the parts dissected away, so as to show the anterior nervous mass (cauliculus), a; the median mass (trabecula), m; the mushroom-bodies (calices), mb; and their stems (peduncles), st. The cellular cap, c, has been raised, so as to display the parts below : com, is a part of the connective uniting the brain and infra-cesophageal ganglia. [Figs. 45-48 are taken from Mr. E. T. Newton’s paper in ‘‘ Journ. Quekett Club,” 1879.] ITS NERVOUS SYSTEM AND SENSE ORGANS. 97 Fig. 48.—Diagrammatic outlines of sections of the Brain of a Cockroach. Only one side of the brain is here represented. The numbers indicate the position in the series of thirty-four sections into which this brain was cut. al, antennary lobe; mb, mushroom bodies (calices), with their cellular covering, c, and their stems (peduncles), st; a, anterior nervous mass (cauliculus); m, median nervous mass (trabecula). From E. T. Newton. H 98 THE COCKROACH : consists of smaller cells without nucleoli. Above the meeting- place of the trabecule is a peculiar laminated mass, the central body, which consists of a network of fibres continuous with the neighbouring ganglionic cells, and enclosing a granular sub- stance. The antennary lobes consist of a network of fine fibres hie 1 AN Wed SS >) "i ‘i te 64a By Ndi pre [J [REZ ep Fig. 49.—Frontal section of Brain of Cockroach. C, cellular layer beneath neuri- lemma; J Cx, inner calix ; O Cx, outer calix; GC, ganglion-cells; P, peduncle ; T, trabecula; Op, optic nerve; AnZ, antennary lobe. X 24. enclosing ganglion cells, and surrounded by a layer of the same. It is remarkable that no fibrous communications can be made out between the calices and the cauliculi, or between the trabecule and the esophageal connectives. Sense Organs. The Eye of Insects. The sense organs of Insects are very variable, both in position and structure. Three special senses are indicated by trans- parent and refractive parts of the cuticle, by tense membranes with modified nerve-endings, and by peculiar sensory rods or ITS NERVOUS SYSTEM AND SENSE ORGANS. 99 filaments upon the antenne. These are taken to be the organs respectively of sight, hearing, and smell. Other sense organs, not as yet fully elucidated, may co-exist with these. The maxillary palps of the Cockroach, for example, are continually used in exploring movements, and may assist the animal to select its food; the cerci, where these are well-developed, and the halteres of Diptera, have been also regarded as sense organs of some undetermined kind, but this is at present wholly conjecture.* | on as & ' 1 ad tae oe a oe Fig. 50.—Plan of Eye of Cockroach, showing the number of facets along ; the principal diameters. as, antennary socket. The compound eyes of the Cockroach occupy a large, irregu- larly oval space (see fig. 50) on each side of the head. The total number of facets may be estimated at about 1,800. The number is very variable in Insects, and may either greatly exceed that found in the Cockroach, or be reduced to a very small one indeed. According to Burmeister, the Coleopterous genus Mordella possesses more than 25,000 facets. Where the facets are very numerous, the compound eyes may occupy nearly the whole surface of the head, as in the Bans Hy. Dragon-fly, or Gad-fly. Together with compound eyes, many Insects are furnished also with simple eyes, usually three in number, and disposed in * It is to be remarked that unusually large nerves supply the cerci of the Cockroach. 100 THE COCKROACH : a triangle on the forehead. The white fenestrae, which in the Cockroach lie internal to the antennary sockets, may represent two simple eyes which have lost their dioptric apparatus. In many larvz only simple eyes are found, and the compound eye is restricted to the adult form; in larval Cockroaches, however, the compound eye is large and functional. Fig. 51.—One element of the Compound Eye of the Cockroach, x 700. Co. F, corneal facets; Cr, crystalline cones; Rm, nerve-rod (rhabdom); RI, retinula of protoplasmic fibrils. To thefright are transverse sections at various levels. Copied from Grenacher. Each facet of the compound eye is the outermost element of a series of parts, some dioptric and some sensory, which forms one of a mass of radiating’ rods or fibres. The facets are ITS NERVOUS SYSTEM AND SENSE ORGANS. 101 transparent, biconvex, and polygonal, often, but not quite regularly, hexagonal. In many Insects the deep layer of each facet is separable, and forms a concavo-convex layer of different texture from the superficial and biconvex lens. The facets, taken together, are often described as the cornea; they repre- sent the chitinous cuticle of the integument. The subdivision of the cornea into two layers of slightly different texture suggests an achromatic correction, and it is quite possible, though unproved, that the two sets of prisms have different dispersive powers. Beneath the cornea we find a layer of erystalline cones, each of which rests by its base upon the inner surface of a facet, while its apex is directed inwards towards ies hyp Fig. 52.—Diagram of Insect Integument, in section. 6m, basement-membrane ; hyp, hypodermis, or chitinogenous layer ; ct, ct’, chitinous cuticle ; s, a seta. the brain. The crystalline cones are transparent, refractive, and coated with dark pigment; in the Cockroach they are comparatively short and blunt. Behind each cone is a nerve- rod (rhabdom), which, though outwardly single for the greater part of its length, is found on cross-section to consist of four components (rhabdomeres)* ; these diverge in front, and receive the tip of a cone, which is wedged in between them; the nerve-rods are densely pigmented. The rhabdom is invested by a protoplasmic sheath, which is imperfectly separated into * The number in Insects varies from eight to four, but seven is usual; four is the usual number in Crustacea. 102 THE COCKROACH : segments (retinule), corresponding in number with the rhab- domeres. ach retinula possesses at least one nucleus. The retinulee were found by Leydig to possess a true visual purple. To the hinder ends of the retinule are attached the fibres of the optic nerve, which at this point emerges through a “ fene- strated membrane.” In the simple eye the non-faceted cornea and the retinula are readily made out, but the crystalline cones are not developed p \ NGS (Of Fig. 53.—-Section through Eye of Dytiscus-larva, showing the derivation of the parts from modified hypodermic cells. JZ, lens; Cr, crystalline cones; R, nerve- rods; WV. Op. optic nerve. From Grenacher. as such. The morphological key to both structures is found in the integument, of which the whole eye, simple or compound, is a modification. A defined tract of the chitinous cuticle becomes transparent, and either swells into a lens (fig. 53), or becomes regularly divided into facets (fig. 55), which are merely the elaboration of imperfectly separated polygonal areas, easily recognised in the young cuticle of all parts of the body. Next, the chitinogenous layer is folded inwards, so as to form a cup, and this, by the narrowing of the mouth, is transformed into a flask, and ultimately into a solid two-layered cellular mass (fig. 53). The deep layer undergoes conversion into a retina, its chitinogenous cells developing the nerve-rods as interstitial structures, while the superficial layer, which loses its functional 4 4 ; ITS NERVOUS SYSTEM AND SENSE ORGANS. 103 importance in the simple eye, gives rise by a similar process of interstitial growth to the crystalline cones of the compound eye (fig. 55). The basement-membrane, underlying the chitin- ogenous cells, is transformed into the fenestrated membrane. The nerve-rods stand upon it, like organ pipes upon the sound- board, while fibrils of the optic nerve and fine trachez pass through its perforations. The mother-cells of the crystalline cones and nerve-rods are largely replaced by the interstitial substances they produce, to which they form a sheath; they are often loaded with pigment, and the nuclei of the primitive-cells can only be distinguished after the colouring-matter has been discharged by acids or alkalis. / envenniah atl R A **Ceeolo oleate} Oot ah i) \\\' \ \ Tf A, Why SC WY we thy N. Op My, i uy AE Fig. 54.—Section through Simple Eye of Vespa. The references as above. Simplified from Grenacher. Dr. Hickson* has lately investigated the minute anatomy of the optic tract in various Insects. He finds, in the adult of the higher Insects, three distinct ganglionic swellings, consisting of a network of fine fibrils, surrounded by a sheath of crowded nerve-cells. Between the ganglia the fibres usually decussate. In the Cockroach, and some other of the lower Insects, the * AEP = 1D ERR ssw om ee a8 ee DLO? thu Re Y, Q) Me Z Y oun @, D The dorsal integument removed and the viscera in place. X 5d. EEE THE ORGANS OF CIRCULATION AND RESPIRATION. 147 Z QD Zw Z Z NWN NOS Fs ‘oy U7 enw GH LLL \\ Fig. 81,—Tracheal System of Cockroach. The viscera removed to show the ventral tracheal communications. xX d.. 148 THE COCKROACH: a Z| Q y 7, PULL x x Z | e e BI 2 S Ze, Al a FALUN Y) mites ON) ANCA a) S ’. S\ os Y A Fig. 82.—Tracheal System of Cockroach. The ventral integument and viscera removed to show the dorsal tracheal communications. ma E® THE ORGANS OF CIRCULATION AND RESPIRATION. 149 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 secreted by an epithelium of nucleated, chitinogenous cells, and outside this is a thin and homogeneous basement mem- brane. The integument, the tracheal wall, and the inner layers of nearly the whole alimentary canal are continuous and equivalent structures. The lining of the larger tracheal tubes at least is shed at every moult, like that of the stomodzeum and proctodzeum. Fig. 83.—Tracheal tube with its epithelium and spiral thread. Slightly altered from a figure given by Chun (Rectal-driisen bei den Insekten, pl. iv., fig. 1). 150 THE COCKROACH: Tracheal Thread. 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 refrac- tive, 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 length making but a few turns round the tube, and ending in a point. The thread of a branch is never continued into a main trunk. Both the thread and the intervening membrane become invisible or faint when the tissue is soaked with a transparent fluid, so as ‘Fig. 84.—Intima (chitinous lining) of a large tracheal tube. The spiral thread divides here and there. Copied from MacLeod, loc. cit., fig. 9. to expel the air. Both, but especially the thread, absorb colouring matter with difficulty. The thread, from its greater thickness, offers a longer resistance to solvents, suck as caustic alkalies, and also to mechanical force; it can therefore be readily unrolled, and often projects as a loose spiral from the end of a torn tube, while the membrane breaks up or crumbles away.* The large tracheal tubes close to the spiracles are without spiral thread, and the intima is here subdivided into polygonal * Investigators are not yet agreed as to the minute structure of the tracheal thread. Chun (Abh. d. Senkenberg. Naturf. Gesells., Bd. X., 1876) considers it an independent chitinous formation, not a mere thickening of the intima. He describes the thread as solid. The intima itself is, he believes, divisible in the larger tubes into an inner and an outer layer, into both of which the thread is sunk. Macloskie (Amer. Nat., June, 1884) describes the spiral as a fine tubule, opening by a fissure along its length. He regards it as a hollow crenulation of the intima, and con- tinuous therewith. Packard (Amer. Nat. Mag., May, 1886) endeavours to show that the thread is not spiral, but consists of parallel thickenings of the intima. He is unable to find proof of the tubular structure, or of the external fissure. We have specially examined the trachea of the Cockroach, and find that the thread can readily be unwound for several turns. It is truly spiral. ee OO ———————— |) THE ORGANS OF CIRCULATION AND RESPIRATION, 151 areas, each of which is occupied by a reticulation of very fine threads. This structure may be traced for a short distance between the turns of the spiral thread. The chitinogenous layer of the tracheal tubes is single, and consists of polygonal, nucleated cells, forming a mosaic pattern, but becoming irregular and even branched in the finest branches. The cell walls are hardly to be made out without staining. Externally, the chitinogenous cells rest upon a delicate basement membrane. Where a number of branches are given off together, the tracheal tube may be dilated. Fine branches, such as accom- pany nerves, are often sinuous. In the very finest branches the tube loses its thread, the chitinogenous cells become irregular, and the intima is lost in the nucleated protoplasmic mass which replaces the regular epithelium of the wider tubes.* The Spiracles. The spiracles of the Cockroach are by no means of compli- cated structure, but their small size, and the differences between. one spiracle and another, are difficulties which cost some pains to overcome. The first thoracic spiracle (fig. 85) is the largest in the body. It lies in front of the mesothorax, between the bases of the first and second legs. It is placed obliquely, the slit being inclined downwards and backwards, and is closed externally by a large, slightly two-lobed valve, attached by its lower border. The aperture immediately within the valve divides into two nearly equal cavities, each of which leads to a separate tracheal trunk ; and between these cavities is a septum, thickened on its free edge, against which the margin of the valve appears to close. A special occlusor muscle arises from the integument below the spiracle, and is inserted into a chitinous process which projects inwardly from the centre of the valve. A second muscle, whose connections and mode of action we have not been able to make out satisfactorily, lies beneath the first, and is inserted into the thickened edge of the septum. * Tt has been supposed that these irregular cells of the tracheal endings pass into those of the fat-body, but the latter can always be distinguished by their larger and more spherical nuclei. 152 THE COCKROACH: The second thoracic spiracle (fig. 86) lies in front of the meta- thorax, between the bases of the second and third legs. It is much smaller and simpler than the first. Its valve is nearly semi-circular, and the free border is strengthened on its deep surface by a chitinous rim, which terminates beyond the end of the hinge of the valve in a process which gives insertion to the occlusor muscle. Fig. 85.—First Thoracic Spiracle (left side), seen from the outside. x 70. V, valve; I, setose lining of valve (mouth of tracheal tube) X 230. The occlusor muscle is shown. The arrow indicates the direction of air entering the spiracle. In the natural position this spiracle is set obliquely, the slit being inclined downwards and backwards. (P. americana.) The abdominal spiracles present quite a different plan of structure. The external orifice is permanently open, owing to the absence of valves, but communication with the tracheal trunk may be cut off at pleasure by an internal occluding apparatus. The external orifice leads into a shallow oval cup, which commu- nicates with the tracheal trunk by a narrow slit, or internal aperture of the spiracle. The chitinous cuticle, surrounding this internal aperture, is richly provided with sete, which are turned towards the opening.* Fig. 87C represents a spiracle * In the first abdominal spiracle the setze are developed only on that lip which carries the bow. : : ; THE ORGANS OF CIRCULATION AND RESPIRATION. 153 seen from within, and shows that the slit divides the cup into two unequal lips, the smaller of which inclines away from the middle line of the body, is movable, and is strengthened on its deep surface by a curved chitinous rod, the “bow” of Landois. Fig. 86.—Second Thoracic Spiracle (left side), seen from the outside. x 70. V, lower (movable) valve. The occlusor muscle is shown. The arrow indicates the direction of air entering the spiracle. (P. americana.) From the opposite lip, a pouch is thrown out, which serves for the attachment of the occlusor muscle. The muscle is inserted into the extremity of the bow, and when it contracts, the bow is pulled over into the position shown in fig. 87D, and the opening is closed. The antagonist muscle, which exists in all the abdominal spiracles, is shown in fig.88 ; it arises from the 154 THE COCKROACH : supporting plate of the spiracle, and is inserted opposite to the occlusor, into the extremity of the bow. rao =I == _ Fig. 87.—Four views of the First Abdominal Spiracle (left side). x 70. The bow is shaded in all the figures. (P. americana.) A—tThe spiracle, seen from the outside; p, lateral pouch; J, internal aperture. B— Do., side view. Cc— Do., — seen from the inside, the aperture open. The occlusor muscle is shown. D—The spiracle, seen from the inside, the aperture shut. ee ee \ on == THE ORGANS OF CIRCULATION AND RESPIRATION, L155 Kach of the eight abdominal spiracles is constructed on this plan; the first merely differs from the others in its larger size and dorsal position, being carried upon the lateral margin of the first abdominal tergum, whereas the others are placed on the side of the body, each occupying an interspace between two wr LB Y Fig. 88.—Abdominal Spiracle (left side) in side view, showing the bow: xX 70; p, lateral pouch of spiracle, seen from within. The tesselated structure of the spiracle and trachea is shown at A (X 230), and the margin of the external aperture at B (x 230). (P. americana.) terga and two sterna. The bow is of about the same length in all; hence the apparent disproportion in the figures of different spiracles. The external aperture of the abdominal spiracles is oval or elliptical, placed vertically and directed backwards. We have already pointed out that the wall of the air-tube, for a short distance from the spiracular orifice, has a tesselated instead of a spiral marking. In the thoracic spiracles the tesselated cells. are grouped round regularly placed sete (fig. 85 I). The chitinous cuticle within the opening is crowded with fine sete, which are often arranged so as to form a fringe on one or both sides of the internal aperture. (Supra, p. 152.) 156 THE COCKROACH : Mechanism of Respiration. In animals with a complete circulation, aérated blood is dif- fused throughout the body by means of arteries and capillaries, which deliver it under pressure at all points. Such animals usually possess a special aérating chamber (lung or gill), where oxygen is made to combine with the hemoglobin of the blood. It is otherwise with Insects. Their blood escapes into great lacunze, where it stagnates, or flows and ebbs sluggishly, and a diffuse form of the internal organs becomes necessary for their free exposure to the nutritive fluid. The blood is not injected into the tissues, but they are bathed by it, and the compact kidney or salivary gland is represented in Insects by tubules, or a thin sheet of finely divided lobules. By a separate mechanism, air is carried along ramified passages to all the tissues. Every organ is its own lung. We must now consider in more detail how air is made to enter and leave the body of an Insect. The spiracles and the air-tubes have been described, but these are not furnished with any means of creating suction or pressure; and the tubes themselves, though highly elastic, are non-contractile, and must be distended or emptied by some external force. Many Insects, especially such as fly rapidly, exhibit rhythmical move- ments of the abdomen. There is an alternate contraction and dilatation, which may be supposed to be as capable of setting up expirations and inspirations as the rise and fall of the diaphragm of a Mammal. In many Insects, two sets of muscles serve to contract the abdomen—viz., muscles which compress or flatten, and muscles which approximate or tele- scope the segments.* In the Cockroach the second set is feebly developed, but the first is more powerful, and causes the terga and sterna alternately to approach and separate with a slow, rhythmical movement; in a Dragon-fly or Humble-bee the action is much more conspicuous, and it is easy to see that the abdomen is bent as well as depressed at each contraction. No special muscles exist for dilating the abdomen, and this seems to depend entirely upon the elasticity of the parts. It was * This subject is treated at greater length in Prof. Plateau’s contribution on Respiratory Movements of Insects. (Infra, p. 159.) THE ORGANS OF CIRCULATION AND RESPIRATION. 157 long supposed that, when the abdomen contracted, air was expelled from the body, and the air passages emptied; that when the abdomen expanded again by its own elasticity, the air passages were refilled, and that no other mechanism was needed. Landois pointed out, however, that this was not enough. Air must be forced into the furthest recesses of the tracheal system, where the exchange of oxygen and carbonic acid is effected more readily than in tubes lined by a dense intima. ut in these fine and intricate passages the resistance to the passage of air is considerable, and the renewal of the air could, to all appearance, hardly be effected at all if the inlets remained open. Landois accordingly searched for some means of closing the outlets, and found an elastic ring or spiral, which surrounds the tracheal tube within the spiracle. By means of a special muscle, this can be made to compress the tube, like a spring clip upon a flexible gas pipe. When the muscle contracts, the passage is closed, and the abdominal muscles can then, it is supposed, bring any needful pressure to bear upon the tracheal tubes, much in the same way as with ourselves, when we close the mouth and nostrils, and then, by forcible contraction of the diaphragm and abdominal walls, distend the cheeks or pharynx. Landois describes the occluding apparatus of the Cockroach as completely united with the spiracle. It consists, according to him, of two curved rods, the “‘ bow” and the “‘ band,” one of which forms each lip of the orifice. From the middle of the band projects a blunt process for the attach- ment of the occlusor muscle, which passes thence to the extremity of the bow. ‘The concave side of each rod is fringed with seta, and turned towards the opening, which lies between the two. Upon this description of the spiracles of the Cock- roach we have to remark that there is no occluding apparatus at all in the thoracic spiracles, which are provided with external valves. In the abdominal spiracles the bow is per- fectly distinct, but the “band” of Landois has no separate existence. Though the actual mechanism in this Insect does not altogether agree with Landois’ description, it is capable of performing the physiological office upon which he justly lays so much stress—viz., the closing of the outlets of the tracheal system, in order that pressure may be brought upon the contained air. 158 THE COCKROACH : The injection of air by muscular pressure into a system of very fine tubes may, however, appear to the reader, as it formerly did to ourselves, extremely difficult or even impossible. Can any pressure be applied to tubes within the body of an Insect which will force air along the passages of (say) ‘0001 in. diameter ? It may well seem that no pressure would suffice to distend these minute tubules, in which the actual replacement of carbonic acid by oxygen takes place, but that the air would either contract to a smaller volume or burst the tissues. If we question the physical possibility of Landois’ explana- tion, an alternative is still open to us. The Jate Prof. Graham has applied the principle of Diffusion to the respiration of animals, and has shown how by a diffusion-process the carbonic acid produced in the remote cavities would be moved along the smaller tubes, and emptied into wider tubes, from which it could be expelled by muscular action. The carbonic acid is not merely exchanged for oxygen, but for a larger volume of oxygen (O95: CQ, 81); and there is consequently a tendency to accumulation within the tubes, which is counteracted by the elasticity of the air vessels, as well as by special muscular contractions.* Whether diffusion or injection by muscular pressure is the chief means of effecting the interchange of gases between the outer air and the inner tissues of the Insect, is a question to be dealt with by physical enquiry. If we suppose two reservoirs of different gases at slightly different pressures to be connected by a capillary tube of moderate dimensions, such as one of the larger trachea of the Cockroach, transference by the molecular movements. of diffu- sion would be small compared with that effected by the flow of the gas in mass. But if the single tube were replaced by a number of others, of the same total area, but of the fineness (say) of the pores in graphite, the flow of the gas would be stopped, and the transference would be effected by diffusion only. We may next consider tubes of intermediate fineness, say a tracheal tubule of the Cockroach at the point * Phil. Mag., 1833. Reprinted in ‘‘ Researches,” p. 44. Graham expressly applies the law of diffusion of gases to explain the respiration of Insects. Sir John Lubbock quotes and comments upon the passage in his paper on the Distribution of the Trachez in Insects. (Linn. Trans. Vol. XXIII.) THE ORGANS OF CIRCULATION AND RESPIRATION, 159 where the spiral thread ceases, and where the exchange of gases through the wall of the tubule becomes comparatively unobstructed. Such a tubule is about ‘0001 in. diameter. If we may extend to such tubules the laws which hold good for the flow of gases in capillary tubes of much greater diameter, the quantity of air which might be transmitted in a given time by muscular pressure of known amount can be determined. Suppose the difference of pressure at the two ends of the tubule to be one-hundredth of an atmosphere, and further, that the tubule is a quarter of an inch long and ‘0001 in. diameter. The tubule would then be cleared out every four seconds. Such a flow of air along innumerable tubules might well suffice for the respiratory needs of the Cockroach. Without laying too much stress upon this calculation, for which exact data are wanting, we may be satisfied that an appreciable quantity of air may be made by muscular pressure to flow along even the finer air passages of an Insect.* Respiratory Movements of Insects. By FELIX 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 all the principal groups, filled an important blank in our knowledge. But, notwithstanding the skill displayed in this research, many questions still remained unanswered, which required more exact methods than mere observation with the naked eye or the simple lens. The writer, who was followed a year later by Langendorff, conceived the idea of studying, by such graphic methods as are now familiar, the respiratory movements of perfect Insects. He * For an explanation of the physical principles involved in this discussion, and for the calculation (based upon our own assumptions), we are indebted to Mr. A. W.. Riicker, F.R.S. 160 THE COCKROACH : has made use of two modes of investigation. The first, or graphic method, in the strict sense of the term, consisted in recording upon a revolving cylinder of smoked paper the respiratory movements, transmitted by means of very light levers of Bristol board, attached to any selected part of the Insect’s exoskeleton. Unfortunately, this plan is only applicable to insects of more than average size. A second method, that of projection, con- sisted in introducing the Insect, carried upon a small support, into a large magic lantern fitted with a good petroleum lamp. When the amplification does not exceed 12 diameters, a sharp profile may be obtained, upon which the actual displacements may be measured, true to the fraction of a millimetre. Placing a sheet of white paper upon the lantern screen, the outlines of the profile are carefully traced in pencil so as to give two superposed figures, representing the phases of inspiration and expiration respectively. By altering the position of the Insect, so as to obtain profiles of transverse section, or of the different parts of the body, and, further, by gluing very small paper slips to parts whose movements are hard to observe, the successive positions of the slips being then drawn, complete information is at last obtained of every detail of the respiratory movements: nothing is lost. This method, similar to that employed by the English phy- siologist, Hutchinson,* is valuable, because it enables us, with a little practice, to investigate readily the respiratory movements of very small Arthropods, such as Flies or Lady-birds. It has this advantage over all others, that it leaves no room for errors of interpretation. Not satisfied with mere observation by such means as these, of the respiratory movements of Insects, the writer has also studied the muscles concerned, and, in common with other physiologists (Faivre, Barlow, Luchsinger, Dénhoff, and Langen- dorff), has examined the action of the various nervous centres upon the respiratory organs. The results at which he has arrived may be summarised as follows :— 1. There is no close relation between the character of the respiratory movements of an Insect and its position in the zoological system. Respiratory movements are similar only * J. Hutchinson, Art. Thorax, Todd’s Cycl. of Anat. and See THE ORGANS OF CIRCULATION AND RESPIRATION, 161 when the arrangement of the abdominal segments, and especially when the disposition of the attached muscles are almost identical. Thus, for example, the respiratory movements of a Cockroach are different from those of other Orthoptera, but resemble those of Hemiptera Heteroptera. 2. The respiratory activity of resting Insects is localised in the abdomen. V. Graber has expressed this fact in a picturesque form, by saying that in Insects the chest is placed at the hinder end of the body. 3. In most cases the thoracic segments do not share in the respiratory movements of an Insect at rest. Among the singular exceptions to this rule is the Cockroach (P. orientalis), in which the terga of the meso- and meta-thoracic segments perform movements exactly opposite in direction to those of the abdomen. (See fig. 89, Ms. th, Mt. th.) Fig. 89.—Profile of Cockroach (P. orientalis). The black surface represents the expiratory contour, while the inspiratory is indicated by a thin line. The arrows show the direction of the expiratory movement. V/s. th., mesothorax ; Mt. th., metathorax. Reduced from a magic-lantern projection. 4, Leaving out of account all details and all exceptions, the respiratory movements of Insects may be said to ‘consist of alternate contraction and recovery of the figure of the abdomen in two dimensions—viz., vertical and transverse. During ex- piration the diameters in question are reduced, while during respiration they revert to their previous amounts. The trans- verse expiratory contraction is often slight, and may be imper- ceptible. On the other hand, the vertical expiratory contraction is never absent, and usually marked. In the Cockroach (P. orientalis) it amounts to one-eighth of the depth of the abdomen (between segments 2 and 3). M 162 THE COCKROACH: 5. Three principal types of respiratory mechanism occur in Insects, and these admit of further subdivision :— (a) Sterna usually stout and very convex, yielding but little. Terga mobile, rising and sinking appreciably. To this class belong all Coleoptera, Hemiptera Heteroptera, and Blattina (Orthoptera). Fig. 90.—Transverse section of Abdomen, Lamellicorn Beetle. The position of the terga and sterna after an inspiration, is indicated by the thick line; the dotted line shows their position after an expiration, and the arrow mack the direction of the expiratory movement. In the Cockroach (Periplaneta) the sterna are slightly raised during expiration. (See figs. 89 and 91.) v Fig. 91.—Transverse section of Abdomen, Cockroach (P. orientalis). (b) Terga well developed, overlapping the sterna on the sides of the body, and usually concealing the pleural membrane, which forms a sunk fold. The terga and sterna approach and recede alternately, the sterna being almost always: the’ more mobile. To this type belong Odonata, Diptera, aculeate Hymenoptera, and Acridian Orthoptera. (Fig. 92.) (c) The pleural membrane, connecting the terga with the sterna, is well developed and exposed on the sides of the body. The terga and sterna approach and recede alter- nately, while the pleural zone simultaneously becomes depressed or returns to its original figure. To this type the writer assigns the ligcectad the Lepidoptera and the true Neve (excluding Phryganide). (Fig. 98.) THE ORGANS OF CIRCULATION AND RESPIRATION. 163 Fig. 92.—Transverse section of Abdomen, Bee (Bombus). 6. Contrary to the opinion once general, changes in length of the abdomen, involving protrusion of the segments and sub- sequent retraction, are rare in the normal respiration of Insects. Such longitudinal movements extend throughout one entire group only—viz., the aculeate Hymenoptera. Isolated examples occur, however, in other zoological divisions. Fig. 95.—Transverse section of Abdomen, Hawk Moth (Sphingina). 7. Among Insects sufficiently powerful to give good graphic tracings, it can be shown that the inspiratory movement is slower than the expiratory, and that the latter is often sudden. 8. In most Insects, contrary to what obtains in Mammals, only the expiratory movement is active; inspiration is passive, and effected by the elasticity of the body-wall. 9. Most Insects possess expiratory muscles only. Certain Diptera (Calliphora vomitoria and FEristalis tenax) afford the simplest arrangement of the expiratory muscles. In these types they form a muscular sheet of vertical fibres, connecting the terga with the sterna, and underlying the soft elastic mem- brane which unites the hard parts of the somites. One of the 164 THE COCKROACH : most frequent complications arises by the differentiation of this sheet of vertical fibres into distinct muscles, repeated in every segment, and becoming more and more separated as the sterna increase in length. (See the tergo-sternal muscles of the Cockroach, fig. 36, p. 76.) Special inspiratory muscles occur in Hymenoptera, Acridiide, and Phryganide. 10. The abdominal respiratory movements of Insects are wholly reflex. Like other physiologists who have examined this side of the question, the writer finds that the respiratory movements persist in a decapitated Insect, as also after destruc- tion of the cerebral ganglia or esophageal connectives; further, that in Insects whose nervous system is not highly concentrated (e.g., Acridiidee and Dragon-flies), the respiratory movements persist in the completely-detached abdomen; while all external influences which promote an increased respiratory activity in the uninjured animal, have precisely the same action upon Insects in which the anterior nervous centres have been removed, upon the detached abdomen, and even upon isolated sections of the abdomen. The view formerly advocated by Faivre, that the metathoracic ganglia play the part of special respiratory centres, must be entirely abandoned. All carefully performed experiments on the nervous system of Arthropoda have shown that each ganglion of the ventral chain is a motor centre, and in Insects a respiratory centre, for the somite to which it belongs. This is what Barlow calls the “ self-sufficiency ”’ of the ganglia. The writer has made similar observations upon the respiration of Spiders and Scorpions ;* but to his great surprise he has been unable either by direct observation, or by the graphic method, or by projection, to discover the slightest respiratory movement of the exterior of the body. This can only be explained by supposing that inspiration and expiration in Pulmonate Arachnida are intra-pulmonary, and affect only the proper respiratory organs. The fact is less surprising because of the wide zoological separation between Arachnida and Insects. * De V’absence de mouvements respiratoires perceptibles chez les Arachnides (Archives de Biologie de Van Beneden et Van Bambeke, 1885.) ———eo ee THE ORGANS OF CIRCULATION AND RESPIRATION. 165 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* 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 fell in spite of its increased warmth. Treviranust gives the carbonic acid exhaled by a Humble-bee as varying from 22 to 174, according as the temperature varied from 56° to 74° F. Larvee often breathe little, especially such as lie buried in wood, earth, or the bodies of other animals. The respiration of pupz is also sluggish, and not a few are buried beneath the ground or shrouded in a dense cocoon or pupa-case. Muscular activity originates the chief demand for oxygen, and accordingly Insects of powerful flight are most energetic in respiration. A rise of temperature proportionate to respiratory activity has been observed in many insects. Newport? tells us how the female Humble-bee places herself on the cells of pups ready to emerge, and accelerates her inspirations to 120 or 130 per minute. During these observations he found in some instances that the temperature of a single Bee was more than 20° above that of the outer air. Some Insects can remain long without breathing. They survive for many hours when placed in an exhausted receiver, or in certain irrespirable gases. Cockroaches in carbonic acid speedily become insensible, but after twelve hours’ exposure to the pure gas they revive, and appear none the worse. H. Miiller§ says that an Insect, placed in a small, confined space, absorbs a// the oxygen. In Sir Humphry Davy’s *‘Consolations in Travel’’|| is a description of the Lago dei * Ueb. d. Respiration der Tracheaten. Chemnitz (1872). + See table in Burmeister’s “ Manual,” Eng. trans. p. 598. + Art. ‘‘ Insecta,” Cyc. Anat. and Phys., p. 989. § Pogg. Ann. 1872, Hft. 3. || Works, Vol. IX., p. 287. This passage has been cited by Rathke. 166 THE COCKROACH. Tartari, near Tivoli, a small lake whose waters are warm and saturated with carbonic acid. Insects abound on its floating islands; though water birds, attracted by the abundance ot food, are obliged to confine themselves to the banks, as the carbonic acid disengaged from the surface would be fatal to them, if they ventured to swim upon it when tranquil. Origin of Tracheal Respiration. Kowalewsky, Biitschli, 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 longi- tudinal 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 distinct contours, fusing to a continuous tissue, in which the individual cells are indicated only by their nuclei, though by appropriate re-agents the cell boundaries can be defined. The ingenious hypothesis propounded by Gegenbaur, that the tracheal tubes of Insects were originally adapted to aquatic respiration, and that the stigmata arose as the scars of disused tracheal gills, has been discussed in chap. iv. Semper has suggested* that tracheze may be modified segmental organs, but the most probable view of their origin is that put forth by Moseley,+ that they arose as ramified cutaneous glands. In Peripatus the openings are distributed irregularly over the body; the external orifices lead to pits, from which simple tubes, with but slight spiral markings, extend into the deeper tissues. * Arbeiten a. d. Zool. Zoot. Inst. Wiirzburg. Bd. 11., 1874. + Phil. Trans., 1874, p. 757. CHAPTER IX. REPRODUCTION. SPECIAL REFERENCES. Branpt, A. Ueber die Hirbhren der Blatta (Periplaneta) orientalis. Mem. Acad. St. Petersb. Ser. 7, Vol. XXI. (1874). [Ovarian Tubes of Cockroach. ] Lacazg-DuTHiers. Rech. sur l’armure génitale femelle des Insectes Orthoptéres. Ann. Sci. Nat., Zool., 3° Sér., Tom. XVII. (1852). [External reproductive organs of female Orthoptera. ] BreRLEsE. Ricerde sugli organi genitali degli Ortotteri. Atti della R. Acad. dei Lincei. Ser. 5, Vol. XI. (1882). [Genital Organs of European Orthoptera. | Kapyi. Beitr. zur Vorgiinge beim. Hierlegen der Blatta Orientalis. Vorliufige Mittheilung. Zool. Anz., 1879, p. 632. [Formation of egg-capsules of Cockroach. } Bream. Comparative structure of the reproductive organs in Blatta germanica and Periplaneta orientalis. Mem. Soc. Ent. St. Petersb., Tom. VIII. (1880). In Russian. [Male organs only. | Ragewsky. Ueber die Geschlechtsorgane von Blatta orientalis, &c. Nachr. d. kais. Gesellsch. d. Moskauer Universitit., Bd. XVI. (1875). [Testes of Cockroach. The original paper is in Russian; an abstract is given in Hofmann and Schwalbe’s Jahresbericht, 1875, p. 425.] BuTscHul. Ban u. Entwickelung d. Samenfaden bei Insekten u. Crustaceen. Zeits. f. wiss. Zool., Bd. XXI., pp. 402-414; 526-534. Pl. xl. xli. (1871). [Spermatozoa and spermatogenesis in the Cockroach. | La VALETTE ST. GEORGE. Spermatologische Beitriige, II. Blatta germanica. Arch. f. mikr. Anat., Bd. XX VII. (1886). [Spermatogenesis in B. germanica.] MorRAVITzZ. Quedam ad anat. Blattze germanice pertinentia. Dissertatio inaugu- ralis. Dorpat. (1853). [An excellent early account of the anatomy of B. germanica, including a description of the male and female organs. The figures are not trustworthy. | Female Reproductive Organs. 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. Trachez and fat-cells tie the ovarian tubes 168 THE COCKROACH: of each side together into a spindle-shaped bundle. Each tube is about ‘4 in. long, and has a beaded appearance, owing to the eggs which distend its elastic wall. It gradually tapers in front; then suddenly narrows to a very small diameter; and lastly, joins with the extremities of the other tubes to form a slender solid filament, which passes towards the heart, and becomes lost in the fat-body. The wall of an ovarian tube consists of a transparent elastic membrane, lined by epithelium, and invested externally by a peritoneal layer of connective tissue. Fig. 94.—Female Reproductive Organs. Od, oviduct; CG, colleterial gland. x 14. The epithelium of an ovarian tube presents some remarkable peculiarities which disguise its true character. High up in the tube, the narrow lumen is occupied by a clear protoplasm, in which nuclei, but no cell walls, can be discerned. Where the tube suddenly widens, large rounded and nucleated masses of protoplasm appear, interspersed with nuclei entangled in a ; = REPRODUCTION, 169 network of protoplasm. Passing down the tube, the large cells, which can now be recognised as eggs, arrange themselves in a single row, to the number of about twenty. They are at first polygonal or squarish, but gradually become cylindrical, and finally oval. Between and around the eggs the nuclei gradually arrange themselves into one-layered follicles, which are attached, not to the wall of the tube, but to the eggs, and travel downwards with them. As the eggs descend, the yolk which they contain increases rapidly, and the germinal vesicle Cia wa Fig. 95.—Ovarian Tube (acetic acid preparation), showing scattered nuclei (upper figure), which ultimately form follicles around the ova (lower figure). Copied from Brandt, loc. cit. 170 THE COCKROACH: and spot (nucleus and nucleolus), which were at first very plain, disappear. A vitelline membrane is secreted by the inner surface, and a chitinous chorion by the outer surface of the egg-follicle. The lowest egg in an ovarian tube is nearly or altogether of the full size; it is of elongate-oval figure, and slightly curved, the convexity being turned towards the uterus. It is filled with a clear albuminous fluid, which mainly consists of yolk. The chorion now forms a transparent yellowish capsule, which under the microscope appears to be divided up into very many polygonal areas, defined by rows of fine dots. These areas probably correspond to as many follicular cells. The convex surface of the chorion is perforated by numerous micropyles, fine pores through which it is probable the spermatozoa gain access to the interior of the egg. The uterus has a muscular wall and a chitinous lining. Two repeatedly branched colleterial glands open into its under side. Of these the left is much the larger, and overlies the other. It consists of many dichotomous tubes, some of which are a little dilated at their blind ends. The gland is much entangled with fat-cells, which make it difficult to unravel. The right gland is probably of no functional importance; the left gland is filled with a milky substance, containing many crystals and a coagulable fluid, out of both of which the egg-capsule is formed.* : At its hinder end the uterus opens by a median vertical slit, which lies in the 8th sternum, into a genital pouch which represents part of the external integument, folded back far into the interior of the abdomen. (See fig. 96.) Upon the dorsal wall of the genital pouch the orifice of the spermatheca is situated.+ This is a short tube dilated at the end, and wound * The crystals have been supposed to consist of oxalate of lime (Duchamp, Rev. des sci. nat. Montpellier, Tom. VIIL.). Hallez observes that they are prismatic, with rhombic base, the angles truncated. They are insoluble in water and weak nitric acid, but dissolve rapidly in strong sulphuric acid without liberation of gas, and still more rapidly in caustic potash. (Compt. Rend., Aug., 1885.) + It is usually stated that the spermatheca of the Cockroach opens into the uterus, as it does in most other Insects, but this is not true. Locusts and Grass- hoppers have the outlet of the spermatheca placed as in the Cockroach; in other European Orthoptera, it lies upon the dorsal wall of the uterus. (Berlese, loc. cit., p. 273.) REPRODUCTION, 171 into a spiral of about one turn. From the tube a cecal process is given off, which may correspond with the accessory gland attached to the duct of the spermatheca in many Insects (¢.g., Coleoptera, Hymenoptera, and some Lepidoptera). The sperma- theca is filled during copulation, and is always found to contain ae ee oe A 9 8 vi 6 av 6 Fig. 96.—Diagram to show the theoretical (upper figure) and actual position of the hinder abdominal sterna in the female Cockroach. JU, uterus; s, spermatheca. The nerve-cord is introduced into both figures. spermatozoa in the fertile female.* The spermatozoa are no doubt passed into the genital pouch from time to time, and there fertilise the eggs descending from the ovarian tubes. The external reproductive organs of the female Cockroach belong to the 7th, 8th, and 9th somites. The 7th sternum is incompletely divided into anterior and posterior sections, and the posterior section is split iato lateral halves. These are joined by a flexible membrane, which admits of the wide separation of the halves, when copulation or the passage of the large egg-capsule renders it necessary. The vertical faces of the membrane, which are pressed together when the parts are at rest, are stiffened by chitinous thickenings. If the succeeding sterna retained their proper place, as they do in some Orthoptera (e.g., the Mole Cricket), the 8th and 9th sterna would project beyond the 7th, while the rectum would * It is a striking proof of the sagacity of Malpighi, that he should have observed in the Silkworm the spermatophore of the male (‘‘in spiram cireumvolutum per- simile semen”) and the spermatheca of the female. His reasoning as to the function of the spermatheca wanted nothing but microscopic evidence of the actual transference of spermatozoa to establish it in all points. Audouin and Siebold supplied what was wanting nearly two centuries later, but they mistook the spirally wound spermatophore for a broken-off penis, and Stein (Weibl. Geschlechtsorgane der Kifer, p. 85) first arrived at the complete proof of Malpighi’s explanation. 172 THE COCKROACH : open beneath the last tergum, and the uterus between the 8th and 9th sterna. In the adult female Cockroach, however, the - 8th and 9th somites are telescoped into the 7th, and completely hidden by it. Their terga are reduced to narrow bands. The Sth sternum forms a semi-transparent plate which slopes down- wards and backwards, and is pierced by a vertical slit, the outlet of the uterus. The upper edge of this sternum is hinged Fig. 97.—-Hinder end of abdomen of female Cockroach. In the upper figure the halves of the 7th sternum are closed ; in the lower figure they are open. upon the projecting basis of the anterior gonapophyses (to be described immediately), and the parts form a kind of spring joint, ordinarily closed, but capable of being opened wide upon occasion. The 9th sternum is a small median crescentic plate, distinct from the 8th ; it supports the spermatheca, whose duct traverses an oval plate which projects from the fore-edge of the sternum. By the telescoping of the 8th and 9th somites the sterna take the position shown in fig. 964, and a new cavity, the genital pouch, is formed by invagination. This receives the extremity of the body of the male during copulation, while it serves as a mould in which the egg-capsule is cast during oviposition. Its chitinous lining resembles that of the outer REPRODUCTION, ] ~] oN integument. The uterus opens into its anterior end, which is bounded by the 8th sternum; the spermatheca opens into its roof, which is supported by the 9th sternum and the gonapop- hyses; while its floor is completed by the 7th sternum and the infolded chitinous membrane. I sab Fig. 98.—External Reproductive Organs of Female. 7%, &c., terga; S’, &e., sterna; G, anterior gonapophysis; G1, its base; g, posterior gonapophyses ; Od, oviduct ; sp, spermatheca; R, rectum. The upper figure shows the parts in oblique profile; the left lower figure is an oblique view from before of the outlet of the uterus, the anterior gonapophyses being cut short ; the right lower figure shows the gonapophyses. Arrows indicate the outlet of the oviduct and uterus. A pair of appendages (anterior gonapophyses) are shown by the development of the parts to belong to the 8th somite. 174 THE COCKROACH : They are slender, irregularly bent, and curved inwards at the tips. A small, forked, chitinous slip Connects them with both the 8th and 9th terga, but their principal attachment is to the upper (properly, posterior), edge of the 8th sternum. The anterior gonapophyses expand at their bases into broad hori- zontal plates, which form part of the roof of the genital pouch. Two pairs of appendages, belonging to the 9th somite, form the posterior gonapophyses. The outer pair are relatively large, soft, and curved: the inner narrow, hard, and straight.* The anterior gonapophyses form the lower, and the posterior the upper jaw of a forceps, which in many Insects can be protruded beyond the body. Some of the parts are often armed with teeth, and the primary use of the apparatus is to bore holes in earth or wood for the reception of the eggs. Hence the apparatus is often called the ovipositor. It forms a promi- nent appendage of the abdomen in such Insects as Crickets, Saw-flies, Sirex, and Ichneumons. The sting of the Bee is a peculiar adaptation of the same organ to a very different purpose. In the Cockroach the ovipositor is used to grasp the egg-capsule, while it is being formed, filled with eggs, and hardened ; and the notched edge (fig. 5, p. 23) is the imprint of the inner posterior gonapophyses, made while the capsule is still soft. The shape of the parts in the male and female indicates that the ovipositor is passive’in copulation, and is then raised to allow access to the spermatheca. 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 vesicule, while they may become consolidated into a * The descriptions and figures of the reproductive appendages of female Orthop- tera by Lacaze-Duthiers (Ann. Sci. Nat., 1852) are so often consulted, that it may be useful to explain how we understand and name the same parts. In pl. xi, fig. 2, 8’ and 9’ are the 8th and 9th terga; the anterior gonapophyses are seen to be attached to them below; «@ (figs. 2 and 4) is the base of the same appendage, but the twisted ends are incorrect; the 8th sternum is seen at the back (figs. 2 and 4); a’ represents the outer, f the inner pair of posterior gonapophyses. ee EET REPRODUCTION, 175 single organ; (2) long coiled vasa deferentia, opening into or close to (3) paired vesicude seminales, which discharge into (4) the ejaculatory duct, a muscular tube, with chitinous lining, by which the spermatozoa are forcibly expelled. Opening into the vesiculze seminales, the ejaculatory duct, or by a distinct external orifice, may be found (5) accessory glands, very variable in form, size, and number. More than one set may oceur in the same Insect. ‘To these parts, which are rarely deficient, are very often appended an external armature of hooks or claspers. The male Cockroach will be found to agree with this description. It presents, however, two peculiarities which are uncommon, though not unparalleled. In the first place the testes are functional only in the young male. They subsequently shrivel, and are functionally replaced by the vesicule seminales and their appendages, where the later transformations of the sperm-cells are effected. The atrophied testes are nevertheless sufficiently large in the adult to be easily made out. Secondly, the accessory glands are numerous, and differ both in function and insertion. ‘T'wo.sets are attached to the vesiculz seminales, and the fore end of the ejaculatory duct (utriculi majores and breviores); another large conglobate gland opens separately to the exterior. We shall now describe the structure of these parts in more detail.* The testes may be found in older larve or adults beneath the fifth and sixth terga of the abdomen. They lie in the fat-body, from which they are not very readily distinguished. Each testis consists of 30-40 rounded vesicles attached by short tubes to the vas deferens.t The wall of the testis * We propose to notice here the chief differences which we have found between the figures of Brehm (/oc. cit.), which are the fullest and best we have seen, and our own dissections. ; Figs. 10, 11 (pp. 169-70). The ejaculatory duct and duct of the conglobate gland are made to end in the penis (infra, p. 178). Figs. 14,15 (p. 173). These figures seem to us erroneous in many respects, such as the median position of the penis and titillator. Fig. 16 (p. 174). The pair of hooks marked EZ are too small, and there are additional plates at the base, which are not figured (see our fig. 102). F (of our fig.) is omitted. +t In Blatta germanica the testes are functional throughout life. They consist of four lobes each. The vasa deferentia are much shorter than in P. orientalis. 176 THE COCKROACII : consists of a peritoneal layer and an epithelium, which is folded inwards along transverse lines. The cells of the epithelium give rise to spermatocysts,* which enclose sperm cells. By oN \ Fig. 99.—1. Male Organs, ventral view. T's, testis; VD, vas deferens; DE, ductus ejaculatorius; U, utriculi majores; wu, utriculi breviores. 2. Do., dorsal view, showing termination of vasa deferentia. 3. Conglobate gland, and its duct. x 8. division of the nuclei of the sperm cells spermatozoa are formed, which have at first nucleated heads and long tails. * The spermatocysts are peculiar to Insects and Amphibia. They arise by division of the spermatospores, or modified epithelial cells, and form hollow cysts, within which sperm cells (or spermatoblasts) are developed by further division. The sperm cells are usually placed radiately around the wall of the spermatocyst. They escape by dehiscence, and are transformed into spermatozoa. REPRODUCTION. 177 Subsequently the enlarged heads disappear. The spermatozoa move actively. In adult males the testes undergo atrophy, but can with care be discovered in the enveloping fat-body. The vasa deferentia are about ‘25 inch in length. They pass backwards from the testes, then turn downwards on each side of the large intestine, and finally curve upwards and forwards, entering the vesiculze seminales on their dorsal side. Each vas deferens divides once or twice into branches, which immediately reunite; in the last larval stage the termination of the passage dilates into a rounded, transparent vesicle. Fig. 100.—Male Organs, side view. 77, seventh tergum; S7, seventh sternum ; Ts, DE, as before. =. * ee a : Y) - Externo-* Fig. 119.—Schematic view of Wing of Paleozoic Cockroach, showing the veins and areas. Now these veins are all present in both front and hind wings of palzeozoic Cockroaches, and also in the hind wings of existing species; but in the front wings or tegmina of the latter the number is never complete, the externomedian vein being always amalgamated either with the scapular, or with the interno- median, and the mediastinal frequently blended with the scapular vein. The hind wings are thus shown to be conservative elements of structure, since they have preserved from the highest antiquity both their transparency and their normal number of P 210 THE COCKROACH veins. They have retained the use to which they were first put, and the changes that have come about, such as the wider expan- sion of the anal area, have been in fuller development of the same purpose; while the front wings, in virtue of their position in repose, have become more and more protectors of the hind wings, and have gradually lost, in part, if not entirely, their original use.’ The hind wings of existing Insects, thus pro- tected, have given less play to selective action, and have become to some degree interpreters for us of the more complicated structure, the more modernised anatomy, the more varied organisation of the front wing. A third distinction between palzozoic and modern Cockroaches is found in the veinlets of the anal area. These, unlike the branches of the other veins, do not part from the main anal vein at various points along its course, but form a series of semi-independent veinlets, and in palzeozoic Cockroaches take the same general course as the main anal vein, or “anal furrow”? (the curved, deeply sunken vein that marks off the anal area from the rest of the front wing, both in ancient and modern Cockroaches), and terminate at sub-equidistant intervals upon the inner margin; while in modern Cockroaches these veins either run sub-parallel to the inner margin and terminate on the descending portion of the anal furrow, or they form a fusiform bundle and terminate in proximity to one another and to the tip of the anal furrow. These differences, which were mentioned by Germar and Goldenberg, and their universality pointed out in my memoir on Paleeozoic Cockroaches,* seem to warrant our separating the older forms from the modern as a family group, under the name of Paleoblattarie ; this family has been thus characterised :— Fore wings diaphanous, generally reticulated, and nearly symmetrical on either side of a median line. Externomedian vein completely developed, forking in the outer half of the wing, its branches generally occupying the apical margin ; internomedian area broad at base (beyond the anal area), rapidly tapering apically, and filled with oblique mostly parallel veins, having nearly the same direction as the anal veinlets, which, like them, strike the inner margin. * Memoirs Bost. Soc, Nat. Hist., III., 23 seq. (1880). OF THE PAST. 211 About eighty palaozoic species have been published up to the present time, and have been grouped in two sub-families and thirteen genera. Besides these, Brongniart has not yet given any hint of how many have been found at Commentry, a French locality which may be expected to increase the number largely, and about twenty undescribed species are known to me from the American Carboniferous rocks. The two tribes or sub-families differ in the structure of the mediastinal vein; in one type (Blattinarie) the branches part from the main stem as in the other veins, at varying distances Fig. 120.—Htoblattina mazona Scudd. xX 3. (The outline of natural size.) Carboniferous, Illinois. along its course (see the figure of Etoblattina); in the other (Mylacride) they spread like unequal rays of a fan from the very base of the wing (see the figure of Mylacris). What is 212 THE COCKROACH curious is that the latter type has been found only in the New World, while the former is common to Europe and America. The latter appears to be the more archaic type, since it is probable that the primeval Insect wing was broad at the base, as is the general rule in palaeozoic wings, and had the veins somewhat symmetrically disposed on either side of a middle line; in this case the mediastinal and anal areas would be somewhat similar and more or less triangular in form, and the Fig. 121.—Mylacris anthracophilum Scudd. xX 2. Carboniferous, Illinois. space they occupied would be most readily filled by radiating veins; such a condition of things, which we find in the Mylacride, would naturally precede one in which the mediastinal vein, to strengthen the part of the wing most lable to strain, should, as in the Blattinarie, follow the basal curve of the costal margin, and throw its branches off at intervals toward the border, much after the fashion of the mediastinal vein. This view of the relative antiquity of the two tribes of Paleoblattarie is supported by the fact that while in both of them the internomedian branches show a tendency to repeat the general course of the anal nervules, as in the corresponding veins of the costal region, this tendency is lost in modern types; and among those ancient Blattinarie, which are esteemed highest in the series, there is a marked tendency toward a loss OF THE PAST, 213 of this repetition of the style of branching of the mediastinal and anal offshoots by the scapular and internomedian respec- tively. A certain amount of geological evidence may also be claimed in support of this view. A survey of the species of the two groups found up to the present time in America, published and unpublished, shows that all the My/acridw are found below the Upper Carboniferous, while more than half the Blattinariv are found in or above it. This results largely from a recent and as yet unpublished discovery of Blattinarie in the Upper Coal Measures of Ohio and West Virginia, which in their general features are much nearer than previously discovered American Cockroaches to the European Blattinariv, the latter of which come generally from Upper Carboniferous beds. The Mylacride have therefore been found in America in strata generally regarded as older than those which in Europe have yielded Cockroaches, and this gives a sufficient explanation why no Mylacride have yet been found in the Old World. In America one is mostly dealing with absolutely older forms, and they naturally give that continent a more old-fashioned look, when we regard the Carboniferous fauna as a whole. As already stated, a wing from the French Silurian (Pal/eoblattina Douvillet Brongn.) has been claimed as a Cockroach, but without good reason, and to see a real old Cockroach one must look to America. Up to this point we have contrasted the paleeozoic Cockroaches with the existing forms only, and finding such important dis- tinctions between them, we naturally turn with some curiosity to the intermediate mesozoic and tertiary formations. Now, not only are the mesozoic species as numerous (actually, but not relatively) as the paleozoic, but a recent discovery of a Triassic fauna of considerable extent, in the elevated parks of Colorado, presents us with a series of intermediate forms between those peculiar to the Coal Measures and those charac- teristic of the later mesozoic rocks. Excluding, however, for a moment this Triassic fauna, we may say of the later mesozoic species that they are Meoblattarie, not Paleoblattarie, though they still show some lingering characteristics of their ancestry. Thus the front wings are in general of a less dense texture than 214 THE COCKROACH in modern times, but without the perfect diaphaneity of the paleeozoic species; in some the anal veins fall in true paleo- blattarian fashion on the inner margin, while in others which cannot be dissociated generically from them, the anal veins are disposed as in modern types. But in all there is a loss of one of the principal veins, or rather an amalgamation of two or more—a characteristic of more fundamental character. As a general rule, moreover, to which we shall again advert, the mass of the species are of small size, in very striking contrast to the older types. To return now to the Triassic deposits of Colorado, we recog- nize here an assemblage of forms of a strictly intermediate character. Here are Paleoblattarie and Neoblattarie, side by side. The larger proportion are Paleobdlattarie, but all of them are specifically, and most of them generically, distinct from paleozoic species, and all rank high among Blattinarie; still further, the species are all of moderate size, their general average being but little above that of mesozoic Cockroaches, ; x Ss Fig. 122.—Weorthroblattina Lakesii Seudd. x 5, Trias, Colorado. and only a little more than half that of paleozoic types. The Jeoblattarie of this Triassic deposit are still smaller, being actually smaller than the average mesozoic Cockroach, and one or two of them, of the genus Neorthroblattina (see figure of NV. Lakesii), have marked affinity to one of the genera of Paleoblattarie (Poroblattina) peculiar to the same beds, differ- ing mainly in the union or separation of the mediastinal and scapular veins; while others, as Scutinoblattina, have a OF THE PAST. 915 Phoraspis-like aspect and density of membrane. This novel assemblage of species bridges over the distinctions between the Paleoblattarie and Neoblattarie. We find, first, forms in which the front wings are diaphanous, with distinct mediastinal and scapular veins, and the anal veinlets run to the border of the wing (Spiloblattina, Poroblattina) ; next, those having a little opacity of the front wings, with blended mediastinal and scapular, and the anal veins as before (some species of Neorthro- biattina); then those with still greater opacity, with the same structural features (other species of Neorthroblattina) ; next, those having a coriaceous or leathery structure, blended mediastinal and scapular, and anal veins falling on the inner margin (some species of Scwtinoblattina) ; and, finally, similarly thickened wings with blended mediastinal and scapular, and anal veins impinging on the anal furrow (other species of Scutinoblattina). It is not alone, however, by the union of the mediastinal and scapular stems that the reduction of the veins in the wings of later Cockroaches has come about; for in many mesozoic types the externomedian vein is blended with one of its neighbours, while in others not only are the mediastinal and scapular united, but at the same time the externomedian and interno- median. As regards the other structural distinction between the Paleoblattarie and Neoblattarie—the course of the anal nervules—there is much diversity, and very imperfect know- ledge, since this very portion of the wing is not infrequently lost, a fracture most readily occurring at the anal furrow. In most of the mesozoic genera, the anal nervules, as far as known, strike the margin; but the larger portion of these show a decided tendency to trend toward the tip of the anal furrow, as in many modern forms. This feature can hardly be considered as firmly established in mesozoic times, and the same genus, as Seutino- blattina, may contain species which differ in this respect. A further peculiarity of mesozoic Cockroaches, already alluded to, is their generally small size. The average length of the front wing of paleozoic Cockroaches has been estimated to be 26 mm., that of the Triassic Paleoblattarie is about 16 mm., while that of the mesozoic Neoblattarie is 125 mm. One 216 THE COCKROACH exception to this small size must be noted in the species from the Jura of Solenhofen, all of which were large and some gigantic, one wing reaching the length of 60 mm., or about the size of our largest tropical Blabere. If we omit these excep- tional forms, the average length of the wing of the mesozoic Cockroach would be scarcely more than 11 mm. Now an average of the 243 species of which the measurements are given in Brunner’s Systéme des Blattaires (1865), gives the length of the front wing of living Cockroaches as a little over 18 mm.; so that the mesozoic Cockroaches were as a rule con- siderably smaller, the palzeozoic Cockroaches much larger, than the living. Nearly eighty species of mesozoic Neoblattarve are known, and they are divided into thirteen genera,* one of which, Mesoblattina (see figure of I. Brodiei), contains upwards of twenty species, mainly from the Lias and Oolites of England. The Upper Oolite has proved the most prolific, considerably Fig. 123.—Mesoblattina Brodiei Scudd. x 4. Purbecks, England. more than half the species having been found in the English Purbecks, while nearly a fourth occur in the Lias of England, Switzerland, and Germany. Many of the English species have been figured in Brodie’s Fossil Insects of the Secondary Rocks of England, in Westwood’s paper on Fossil Insects in the tenth volume of the Quarterly Journal of the Geological Society, and in the memoir alluded to above. No species has yet been found in rocks of different geological horizons, and the * See a paper on mesozoic Cockroaches now printing in the Memoirs Bost. Soc. Nat. Hist., Vol. TIL, p. 439 seq. OF THE PAST. 217 genera of the Trias are peculiar to it. So, too, are some of the genera of the Oolite, but all of the Liassic genera occur also in the Oolite. Among these mesozoic Cockroaches are some of very peculiar aspect; one, Blattidium (see figure of B. Simyrus), found only in the lower Purbecks, has ribbon-shaped wings with parallel —_— fi ; Fig. 124.—Blattidium Simyrus Westw. x 3. Lower Purbecks, England. sides, longitudinal neuration, and anal nervures with a course at right angles to their usual direction ; another, Pterinoblattina (see figure of P. intermizxta), geologically widespread, is very broad, more or less triangular, and has an exceedingly fine and delicate neuration, so arranged as to resemble the barbs of a feather. A comparison of the neuration of the tegmina of mesozoic and recent Cockroaches, to determine as far as possible the immediate relations of the former to existing types, gives as yet little satisfaction. The prolific genera, Wesoblattina and Rithma, may be said to bear considerable resemblance to the Phyllodromide, and the peculiar neuration of Elisama is in part repeated in the Panchloride, as well as in some Phyllodromide 218 THE COCKROACH and Epilampride. Scutinoblattina also reminds one in certain features of some LEpilampride, like Phoraspis. The other genera appear to have no special relations to any existing type. Asa whole, it would appear as if the Blattarie spinose approached closer to the mesozoic forms than do the Blattarie mutice. Fig. 125.—Pterinoblattina intermixta Scudd. x 4. Upper Lias, England. As to the tertiary Cockroaches we know very little, exceed- ingly few having been preserved, even in amber—that wonderful treasury of fossil Insects. Here first we come across apterous forms, Polyzosteria having been recognised in Prussian amber,* together with winged species, which seem to be Phyllodromide ; these are the only Blattarie spinose known from the Tertiaries. Of the other group, we have Zetobora, one of the Panchiloride, and Paralatindia, one of the Corydide, from American rocks, and Heterogamia and Homeo- gamia, one from Parschlug in Steiermark, the other from Florissant in Colorado, belonging to the sub-family Heteroga- midce. Others are mentioned, generally under the wide generic term Blatta, from Oeningen, Eisleben, Rott, and even from Spitzbergen and Greenland ; but little more than their names are known to us. Paralatindia, from the Green River beds of Wyoming, U.S., is the only tertiary Cockroach yet referred to an extinct genus; but close attention has not yet been paid even to the few tertiary Cockroaches which we know. There is no reason to suppose that they will be found to differ more from the existing types than is generally the case with other * The wingless creature from the Carboniferous deposits of Saarbriicken, described by Goldenberg as a Cockroach, under the name of Polyzosterites granosus, appears to be a Crustacean. OF THE PAST. 219 Insects. The more we learn of csenozoic Insects, the more truly do we find that the early Tertiary period was in truth the dawn of the present, the distinction between the faunas of these remotely separated times (though not to be compared in character) being scarcely greater than is found to-day between the Insects of the temperate and torrid zones. We began this review with the statement that no Insect was so important palzontologically as the Cockroach. This would more clearly appear had we space to pass in review the geologi- cal history of all the Insect tribes; for then it could be shown that it was only in the passage from palzeozoic to mesozoic times that the great ordinal groups of Insects were differentiated, and that the Triassic period therefore becomes the expectant ground of the student of fossil Insects. Up to the present time we do not know half a dozen Insects besides Cockroaches from these rocks. Yet, notwithstanding this advantage on the part of the Cockroaches, how meagre is the history, how striking the “imperfection of the geological record” concerning them, the following tabulation of the fossil species by their genera will show. It here appears that there are about 80 species known from the paleeozoic rocks, two or three more than that from the mesozoic, and only nine from the czenozoic! When we call to mind that half the paleozoic Insects were Cockroaches, and that seven or eight hundred species exist to-day, what shall we say of the paltry dozen* from the rich tertiaries? Shall we claim that these figures represent their true numerical proportion to their numbers in the more distant past? Then, indeed, must the palzeozoic period have been the Age of Cockroaches; for all research into the past shows that a type once losing ground continues to lose it, and does not again regain its strength. The Cockroaches of to-day are no longer, as once, a dominant group; they are but a fragment of the world’s Insect-hosts; yet even now the species are numbered by hundreds. If this be a waning type, what must its numbers have been in the far- off time, when the warm moisture which they still love was the prevailing climatic feature of the world; and how few of that vast horde have been preserved to us! The housekeeper will thank God and take courage. * This includes all possible forms; our table shows but nine. GEOLOGICAL DISTRIBUTION OF FOSSIL COCKROACHES. Figures in italics represent the number of American species ; in roman, of European. PALHOBLATTARIA. Mylacride—Mylacris Promylacris Paromylacris Lithomylacris Necymylacris Blattinarie—Etoblattina Spiloblattina Archimylacris .. Anthracoblattina!) .. Gerablattina Hermatoblattina Progonoblattina Oryctoblattina .. Petrablattina Poroblattina NEOBLATTARLE. Ctenoblattina .. Neorthroblattina .. Rithma .. SA Mesoblattina .. Elisama .. .. Pterinoblattina Blattidium Nannoblattina Dipluroblattina Diechoblattina Scutinoblattina Legnophora Aporoblattina.. Not yet referred to sub-families Phyllodromide—“ Blatta ” Periplanetide—Polyzosteria .. Panchloride—Zetobora .. Corydide—Paralatindia . . Heterogamide—Homeogamia Heterogamia GRAND TOTALS .. Carboniferous. 10 I L : 2 2 oleate I 1 a ees Zz ey. 1 1 uf, (23)| (6) 23 6 (41) | (11) (10)| 4] 1 1 ¢ 5 | 8 ug i} 4! ete x| @ S| 2c ee z . 10 ae 1 g 1 _ 4 a 2 1 28 if 3 a7 13 Py 12 ‘its 2 re : 3 2 4 2 2s = =) _ — a tog : . BR Werks aves : ie 2/10 12 7 Vas 2 1 1} Ss 6 ; 3-| *6 9 a 2 2 3 3 1 1 3a 2 2, 3 ai > 1 1 de 3) Sais 9 : (8) | (17)| (52) (77) co *| oe eee 3 3 2 2 Z 1 q u a 1 43 1 1 (8) | (1) } (9) 8} 1 SamurEL H. ScuppDEr. APPENDIX. PARASITES OF THE COCKROACH. Spirillum, sp. [ Vibrio]. SCHIZOMYCETES. Rectun. Ref.—Biitschli, Zeits. f. wiss. Zool., Bd. X-XT., p. 254 (1871). Hygrocrocis intestinalis, Val. CYANOPHYCE. Filaments of a very minute Alga abound in the rectum of the Cockroach, where this species is said by Valentin to occur. The intestine of the Crayfish is given as another habitat. Leidy observes that the filaments which he found in the rectum of the Cockroach are inarticulate, and do not agree with Valentin’s description of the species. Ref.— Valentin, Repert. f. Anat. u. Phys., Bd. I., p. 110 (1836) ; Robin, Végét. qui croissent sur Homme, p. 82 (1847); Leidy, Smithsonian Contr., Vol. V., p. 41 (1853) ; Bitschli, Zeits. f. wiss. Zool., Bd. XXI., p. 254 (1871). Endameba (Ameba) latte, Bitschli. RHIZOPODA. Rectum. Ref—Siebold, Naturg. wirbelloser Thiere (1839) jide Stein ; Stein, Organismus d. Infusions-thiere, Bd. II., p. 345 (1867) ; Bitschli, Zeits. f. wiss. Zool., Bd. XXX., p. 273, pl. xv. (1878) ; Leidy, Proc. Acad. N. 8. Phil., Oct. 7th, 1879, and Freshwater Rhizopods of N. America, p. 300 (1879). Gregarina (Clepsidrina) Blattarum, Sieb. GREGARINIDA. Encysted in chylific stomach and gizzard; free in large intestine. ftef—Siebold, Naturg. wirbelloser Thiere, pp. 56, 71 (1839) ; Stein, Mull. Arch., 1848, p. 182, pl. ix., figs. 38, 39; Leidy, Trans. Amer. Phil. Soc., Vol. X., p. 239 (1852); Biitchsli, Zeits. f. wiss. Zool., Bd. XXI., p. 254 (1871), and Bd. XXXV., p. 384 (1881) ; Schneider, Grégarines des Invertébrés, p. 92, pl. xvii. figs. 11, 12 (1876). 222, APPENDIX. Nyctotherus ovalis, Leidy. INFUSORIA. 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. kénigl. Bohm. Ges., 1860, pp. 49, 50. Lophomonas Blattarum, Stein. INFUSORIA. Rectum. Ref.—Stein (loc. cit.) ; Biitschli, Zeits. f. wiss. Zool., Bd. XXX., p. 258, plates xiii., xv. (1878). L. striata, Bitschli. INFUSORIA. Rectun. Ref.—Biitschli, Zeits. f. wiss. Zool., Bd. XXX., p. 261, plates xiii., xv. (1878). Gordius, sp. NEMATELMINTHA. Specimens in the Museum at Hamburg, from Venezuela. Obtained from some species of Cockroach, Oxyuris Diesingi, Ham. : NEMATELMINTHA. Rectum, frequent. fef—Hammerschmidt, Isis, 1838; Biitschli, Zeits. f. wiss. Zool., Bd. XXI., p. 252, pl. xxi: (1871). O. Blatte orientalis, Ham. NEMATELMINTHA. Rectum (much rarer than O. Diesing?). Ref—Hammerschmidt (loc. cit.) ; Biitschli, Zeits. f. wiss. Zool., Bd. XXI., p. 252, pl. xxii. (1871). Other species of Oxywris are said to occur in the same situation, e.g., O. gracilis and O. appendiculata (Leidy, Proc. Acad. N. 8. Phil., Oct. 7th, 1879), and O. macrowra (Radkewisch, quoted by Van Beneden in Animal Parasites, Engl. trans., p. 248). Filaria rhytipleurites. NEMATELMINTHA. Encysted in the fat-body of the Cockroach ; sexual state in the alimentary canal of the Rat. Spiroptera obtusa is similarly shared by the Meal-worm (larva of Yenebrio molitor) and the Mouse. Ref.—Galeb, Compt. Rend., July 8th, 1878. bo we APPENDIX. 22% Acarus, sp. ARACHNIDA, Found by Cornelius upon the sexual organs of a male Cockroach, Ref.—Cornelius, Beitr. zur nihern Kenntniss von Periplaneta orientalis, p. 35, fig. 23 (1853). Evania appendigaster, L. Insecta (ymenoptera). A genus of Ichneumons, parasitic upon Periplaneta and Blatta. Ref.—Westwood, Trans. Ent. Soc., Vol. ILT., p. 237 ; Ib., Ser. IL., Vol. I., p. 213. Symbius Blattarwm, Sund. Insecta (Coleoptera). The apterous female is parasitic upon P. americana and B. germanica. Ref.—Sundevall, Isis, 1831. SENSE OF SMELL IN INSECTS. Since the printing of the sheets which describe the organs of special sense, we have become acquainted with two experimental researches of recent date, instituted for the purpose of determining whether other organs, besides the antennz, may be specially con- cerned with the perception of odours by Insects. Prof. Graber (Biol. Centralblatt, Bd. V., 1885) has described extensive and elaborate experiments upon various Insects, tending to the conclusion that the palps and the cerci may be sensitive to odours, and that in special cases the palps may be even more sensitive in this respect than the antennze. Cockroaches, decapi- tated, but kept alive for some days, were found to perceive odours by means of their cerci. His general conclusion is that Insects have no special sense of smell], but that various parts of the surface of the body are furnished with nerve-endings capable of perceiving strong odours. Prof. Graber’s results are known to us only through the abstract given by Prof. Plateau in the paper next to be mentioned. Prof. Plateau (Compt. rend. de la Soc. Entom. de Belgique, 1886) relates experiments upon the powers of scent resident in different organs of the Cockroach. Two Cockroaches had their palps (max- illary and labial) removed ; two others had the antenne removed. An evaporating dish, 8 inches in diameter, was then partly filled with 224 APPENDIX. fine sand. In the centre of the dish was set a circular box of card, | without bottom, 2 inches in diameter, and 14 inches high. In this box — bread moistened with beer, a bait very attractive to Cockroaches, was placed, and renewed daily. The four Cockroaches were allowed to run. about in the dish outside the box, and to feed upon the bread at pleasure by climbing over the ‘enclosure. Observations were made late at night for a month, when it was found that, except on the first night, when the Insects ran all over the dish, none of the Cockroaches without antenne made their way to the food ; while twenty-three times one of the Cockroaches without palps,. ‘but with antenne intact, was found to be feeding ; in one instance, both were so found. Plateau observes that a special sense of smell can only be claimed for organs which are able to detect faint and distant odours, and that experiments made with powerful odours close to the body of the Insect may lead to fallacious results. The perception of faint odours cannot be effected by the palps or cerci of the Cockroach, -but only by the antenne. THE END. PRINTED BY McCORQUODALE & CO, Limtrep, LEEDs. “ i i , Lie a) me sue : EN ah Ny ; at ae mG ie Date Due BRODART, INC Cat. No. 23 233 Printed in USA BINDING SECT. ¢rp | University of Toronto Z oo] es DO NOT. REMOVE THE CARD Ze | FROM THIS POCKET Acme Library Card Pocket LOWE-MARTIN CO. LIMITED 2 900 OF 2 60 LL 6€ 2 Wall SOd JIHS AVE JONVY CG M3IASNMOG LV 1LN