O; ii CD m D A TEXT-BOOK OF ENTOMOLOGY TEXT-BOOK OF ENTOMOLOGY INCLUDING THE ANATOMY, PHYSIOLOGY, EMBRYOLOGY AND METAMORPHOSES OF INSECTS FOR USE IN AGRICULTURAL AND TECHNICAL SCHOOLS AND COLLEGES AS WELL AS BY THE WORKING ENTOMOLOGIST BY ALPHEUS S. PACKARD, M.D., PH.D. PROFESSOR OF ZOOLOGY AND GEOLOGY, BROWN UNIVERSITY AUTHOR OF " GUIDE TO STUDY OF INSECTS," " ENTOMOLOGY FOR BEGINNERS," ETC. THE MACMILLAN COMPANY LONDON: MACMILLAN & CO., LTD. 1898 All rights reserved COPYRIGHT, 1898, BY THE MACMILLAN COMPANY. Nortooofc J. S. Gushing & Co. — Berwick & Smith Norwood Mass. U.S.A. PEEFACE IN preparing this book the author had in mind the wants both of the student and the teacher. For the student's use the more diffi- cult portions, particularly that on the embryology, may be omitted. The work has grown in part out of the writer's experience in class work. In instructing small classes in the anatomy and metamorphoses of insects, it was strongly felt that the mere dissection and drawing of a few types, comprising some of our common insects, were by no means sufficient for broad, thorough work. Plainly enough the laboratory work is all important, being rigidly disciplinary in its methods, and affording the foundation for any farther work. But to this should be added frequent explanations or formal lectures, and the student should be required to do collateral reading in some general work on structural and developmental entomology. With this aim in view, the present work has been prepared. It might be said in explanation of the plan of this book, that the students having previously taken a lecture course in the zoology of the invertebrates, were first instructed in the facts and conclusions bearing on the relations of insects to other Arthropoda, and more especially the anatomy of Peripatus, of the Myriopoda, and of Scolo- pendrella. Then the structure of Campodea, Machilis, and Lepisma was described, after which a few types of winged insects, beginning with the locust and ending with the bee, were drawn and dissected ; the nymph of the locust, and the larva and pupa of a moth and of a wasp and bee being drawn and examined. Had time permitted, an outline of the embryology and of the internal changes in flies during their metamorphoses would have been added. vi PREFACE This book gives, of course with much greater fulness and detail for reference and collateral reading, what we roughly outlined in our class work. The aim has been to afford a broad foundation for future more special work by any one who may want to carry on the study of some group of insects, or to extend in any special direc- tion our present knowledge of insect morphology and growth. Many of our entomologists begin their studies without any pre- vious knowledge of the structure of animals, taking it up as an amusement. They may be mere collectors and satisfied simply to know the name of their captures, but it is hoped that with this book in their hands they may be led to desire farther information regarding what has already been done on the structure and mode of growth of the common insects. For practical details as to how to dissect, to make microscopic slides, and to mount and preserve insects generally, they are referred to the author's "Entomology for Beginners." It may also be acknowledged that even in our best and latest general treatises on zoology, or comparative anatomy, or morphology, the portion related to insects is scarcely so thoroughly done as those parts devoted to other phyla, that of Lang, however, his invaluable Comparative Anatomy, being an exception. On this account, there- fore, it is hoped that this hiatus in our literature may be in a degree filled. The author has made free use of the excellent article "Insecta" of Newport, of Lang's comprehensive summary in his most useful Text-book of Comparative Anatomy, of Graber's excellent Die Insecten, of Miall and Denny's The Structure and Life-History of the Cockroach, and of Sharp's Insecta. Kolbe's Einfuhrung has been most helpful. But besides these helps, liberal use has been made of the very numerous memoirs and monographic articles which adorn our entomological literature. The account of the embryology of insects is based on Korschelt and Heider's elaborate work, Lehrbuch der Vergleichenden Entwicklungsgesehichte der Wirbellosen Thiere, the illustrations of this portion being mainly taken from it, through the Messrs. Swan Sonnenschein & Co., London. PREFACE vii Professor H. S. Pratt has kindly read over the manuscript and also the proofs of the portion on embryology and metamorphoses, and the author is happy to acknowledge the essential service he has rendered. The bibliographical lists are arranged by dates, so as to give an idea of the historical development of each subject. The aim has been> to make these lists tolerably complete and to include the earliest, almost forgotten works and articles as well as the most recent. Much care has been taken to give due credit either to the original sources from which the illustrations are copied, or to the artist ; about ninety of the simpler figures were drawn by the author, many of them for this work. For the use of certain figures acknowledg- ments are due to the Boston Society of Natural History, to the Division of Entomology, U. S. Department of Agriculture, through the kind offices of Mr. L. 0. Howard, and to the Illinois State Laboratory of Natural History, through Professor S. A. Forbes and Mr. C. A. Hart. Professor AV. M. Wheeler, of the University of Chicago, has kindly loaned for reproduction several of his original drawings published in the Journal of Morphology. A number are reproduced from figures in the reports of the United States Ento- mological Commission. PROVIDENCE, R.I., March 4, 1898. TABLE OF CONTENTS PART I. MORPHOLOGY AND PHYSIOLOGY PAGB POSITION OF INSECTS IN THE ANIMAL KINGDOM ... 1 RELATIONS OF INSECTS TO OTHER ARTHROPODA .... 2 The Crustacea ... 4 The Merostomata .......... 5 The Trilobita 5 The Arachnida ... 6 Relations of Peripatus to insects ....... 9 Relation of Myriopods to insects ....... 11 Relations of the Symphyla to insects .... 18 Diagnostic or essential characters of Symphyla ... .22 INSECTA (HEXAPODA) ........... 26 Diagnostic characters of insects ........ 26 1. EXTERNAL ANATOMY a. Regions of the body ......... 27 b. The integument (exoskeleton) 28 Chitin 29 c. Mechanical origin and structure of the segments (somites, arthro- meres, etc.) ......... 30 d. Mechanical origin of the limbs and of their jointed structure . 35 THE HEAD AND ITS APPENDAGES ........ 42 «. The head 42 The labrum . 42 The epipharynx and labrum-epipharynx ..... 43 Attachment of the head to the trunk ..... 46 The basal or gular region of the head ... 46 The occiput ........ 48 The tentorium 49 Number of segments in the head ...... 50 The composition of the head in the Hymenoptera . . 55 28977 x TEXT-BOOK OF ENTOMOLOGY PAGE b. Appendages of the head .... .57 The antennae .......... 57 The mandibles .59 The first maxillaj .62 The second maxillae ...... .68 The hypopharynx .... 70 Does the hypopharynx represent a distinct segment ? . . 82 THE THORAX AND ITS APPENDAGES ...... .86 a. The thorax : its external anatomy ... .86 The patagia .89 The tegulae .89 The apodemes .92 The acetabula .... .94 b. The legs : their structure and functions ... .95 Tenent hairs .99 Why do insects have but six legs ? . . . . . 100 Loss of limbs by disuse ........ 101 c. Locomotion (walking, climbing, and swimming) .... 103 Mechanics of walking . 103 Locomotion on smooth surfaces ...... Ill Climbing .116 The mode of swimming of insects 116 d. The wings and their structure 120 The veins .121 The squamae ........ . 123 The halteres .124 The thyridium .124 The tegmina and hemelytra .... . 124 The elytra .124 e. Development and mode of origin of the wings . . 126 Embryonic development of the wings ... .126 Evagination of the wing outside of the body . .132 Extension of the wing ; drawing out of the tracheoles . . 133 /. The primitive origin of the wings .... . 137 The development and structure of the tracheae and veins of the wing .... .144 y. Mechanism of flight • 148 Theory of insect flight .... 150 Graber's views as to the mechanism of the wings, flight, etc. . 153 THE AllDOMEN AND ITS APPENDAGES . 162 The median segment 163 The cercopoda . . 164 The ovipositor and sting . • 1(>|7 The styles and genital claspers (Rhabdopoda) . . 176 Velum penis . . .181 The suranal plate 181 TABLE OF CONTENTS xi PAGE The podical plates or paranal lobes ... ... 182 The infra-anal lobe ... .... .183 The egg-guide . . ...... 183 THE ARMATURE OF INSECTS : SET^E, HAIRS, SCALES, TUBERCLES, ETC. . 187 The cuticula . . '. ........ 187 Setaj . ........... 188 Glandular hairs and spines ......... 190 Scales . . .... .193 Development of the scales ......... 195 Spinules, hair-scales, hair-fields, and androconia ..... 197 THE COLORS OF INSECTS .......... 201 Optical colors ........... 201 Natural colors ........... 203 Chemical and physical nature of the pigment ..... 206 Ontogenetic and phylogenetic development of colors .... 207 2. INTERNAL ANATOMY THE MUSCULAR SYSTEM . . . . . . . . .211 Musculature of a caterpillar ......... 213 Musculatui'e of a beetle ......... 213 Minute structure of the muscles ......... 215 Muscular power of insects . . . . . . . . ... 2J7.; THE NERVOUS SYSTEM .......... a. The nervous system as a whole ....... 22.2 b. The brain .......... . 226' The optic or procerebral segment . . . . . .231 Procerebral lobes ......... 232 The mushroom or stalked bodies ...... 233 Structure of the mushroom bodies ...... 234 The central body ... ... .237 The antenna! or olfactory lobes (Deutocerebrum) . . . 237 The oesophageal lobes (Tritocerebrum) ..... 237 c. Histological elements of the brain ....... 238 d. The visceral (sympathetic or stomatogastric) system . . . 238 f. The supraspinal cord ....... . 240 /. Modifications of the brain in different orders of insects . . . 240 g. Functions of the nerve-centres and nerves ..... 243 THE SENSORY ORGANS .......... 249 a. The eyes and insect vision ..... . 249 The simple or single-lensed eye (ocellus) . . . 249 The compound or facetted eye (ommateum) . . . 250 The facet or cornea ...... . 250 The crystalline lens or cone ....... 251 xii TEXT-BOOK OF ENTOMOLOGY PAGE The pigment .......... 253 The basilar membrane . 253 The optic tract . • . 253 Origin of the facetted eye .... . 255 Mode of vision by single eyes or ocelli ..... 255 Mode of vision by facetted eyes 256 The principal use of the facetted eye to perceive the move- ments of animals ........ 259 How far can insects see ? . 260 Relation of sight to the color of eyes 260 The color sense of insects .... . 200 b. The organs of smell ....... • 264 Historical sketch of our knowledge of the organs of smell . 204 Physiological experiments ..... . 268 Relation of insects to smelling substances before and after the loss of their antennae • 260 Experiments on the use of the antennae in seeking for food . 270 Experiments testing the influence of the antennae of the males in seeking the females .... . 270 Structure of the organs of smell in insects . . .271 c. The organs of taste ....... .281 Structure of the taste organs . Distribution in different orders of insects 282 Experimental proof ......... 286 d. The organs of hearing ....... . 287 The ears or tympanal and chordotonal sense-organs of Ortliop- tera and other insects ....... 288 Antennal auditory hairs ........ 202 Special sense-organs in the wings and halteres .... 293 e. The sounds of insects • 293 THE DIGESTIVE CANAL AND ITS APPENDAGES ...... 297 rt. The digestive canal ........ • 30-_> The oesophagus .......... 303 The crop or ingluvies ..... . 303 The " sucking stomach " or food-reservoir . . . 305 The fore-stomach or proventriculus ...... 306 The cesophageal valve ...... .311 Proventricular valvule ...... • 31:5 The peritrophic membrane . . . . . . .31:'. The mill-intestine ....... • 314 Histology of the mid-intestine ..... . 310 The hind-intestine .31(5 Large intestine ........ • 316 The ileum • 317 The gastro-ileal folds . . . . . . .317 The colon ......... • 317 The rectum 318 TABLE OF CONTENTS xiii PAGE The vent (anus) ......... 319 Histology of the digestive canal ...... 320 b. Digestion in insects .......... 324 The mechanism of secretion .... . . 326 Absorbent cells .......... 328 THE GLANDULAR AND EXCRETORY APPENDAGES OF THE DIGESTIVE CANAL, 331 a. The salivary glands .......... 331 b. The silk or spinning glands, and the spinning apparatus. . . 339 The process of spinning ........ 340 How the thread is drawn out ....... 343 Appendages of the silk-gland (Filippi's glands) . . . 345 c. The ctecal appendages 347 d. The excretory system (urinary or Malpighian tubes) . . . 348 Primitive number of tubes ....... 353 e. Poison-glands 357 /. Adhesive or cement-glands ........ 360 g. The wax-glands . . . . . . . . . .361 h. " Honey-dew " or wax-glands of Aphids ..... 364 i. Dermal glands in general ........ 365 DEFENSIVE OR REPUGNATORIAL SCENT-GLANDS ...... 368 Eversible coxal glands 369 Foetid glands of Orthoptera ......... 369 Anal glands of beetles 372 The blood as a repellent fluid ........ 374 Eversible glands of caddis-worms and caterpillars .... 375 The osmeterium in Papilio larvae ........ 377 Dorsal and lateral eversible metameric sacs in other larvse . . . 377 Distribution of repugnatorial or alluring scent-glands in insects . . 382 THE ALLURING OR SCENT-GLANDS ........ 391 THE ORGANS OF CIRCULATION ......... 397 a. The heart 397 The propulsatory apparatus 401 The supra-spinal vessel ........ 403 The aorta 404 The pericardial cells 405 Pulsatile organs of the legs ....... 405 b. The blood 407 The leucocytes .......... 407 c. The circulation of the blood 409 Effects of poisons on the pulsations ...... 412 THE BLOOD TISSUE 419 a. The fat-body 419 b. The pericardial fat-body or pericardial ceils ..... 420 Leucocytes or phagocytes in connection with the pericardial cells 421 xiv TEXT-BOOK OF ENTOMOLOGY PAGE c. The oenocytes ........... 423 d. The phosphorescent organs .... ... 424 Physiology of the phosphorescence ...... 426 THE RESPIRATORY SYSTEM . . .... . . 430 a. The tracheae . . 431 Distribution of the tracheae ....... 432 b. The spiracles or stigmata 437 The position and number of pairs of stigmata .... 439 The closing apparatus of the stigma 441 c. Morphology and homologies of the tracheal system . . . 442 d. The spiral threads or tsenidia ........ 444 e. Origin of the tracheae and of the " spiral thread ". . . 447 Internal, hair-like bodies ........ 451 /. The mechanism of respiration and the respiratory movements of insects .......... 451 g. The air-sacs • 456 The use of the air-sacs 457 h. The closed or partly closed tracheal system ..... 459 i. The rectal, tracheal gills, and rectal respiration of larval Odonata and other insects ........ 463 j. Tracheal gills of the larvfe of insects ...... 466 Blood-gills 475 k. Tracheal gills of adult insects . . 476 THE ORGANS OF REPRODUCTION . 485 a. The male organs of reproduction ....... 494 The testes . 495 The seminal ducts ......... 496 The ejaculatory duct ........ 497 The accessory glands 497 The spermatozoa ......... 497 Formation of the spermatozoon .... . 498 b. The female organs of reproduction ..... . 500 The ovaries and the ovarian tubes ... . 500 Origin of incipient eggs in the germ of the testes . . . 504 The bursa copulatrix ....... . 505 The spermatheca ....... . 506 The colleterial glands ..... . 506 The vagina or uterus .... . 507 Signs of copulation in insects ....... 507 PART II. EMBRYOLOGY OF INSECTS a. The egg .... • 515 Mode of deposition .518 Vitality of eggs 520 TABLE OF CONTENTS xv PAGE Appearance and structure of the ripe egg ..... 520 The egg-shell and yolk-membrane ....... 520 The micropyle ........... 522 Internal structure of the egg ........ 5'24 b. Maturation or ripening of the egg ........ 525 c. Fertilization of the egg .......... 525 d. Division and formation of the blastoderm ...... 520 e. Formation of the first rudiments of the embryo and of the embryonic membranes .......... 531 Formation of the embryonic membranes ..... 532 The gastrula stage .......... 535 Division of the embryo or primitive band into body-segments . 536 Differences between the invaginated and overgrown primitive band, 538 Revolution of the embryo where the primitive band is invaginated, 540 /. Formation of the external form of the body ...... 542 Origin of the body-segments 542 The procephalic lobes 544 Fore-intestine (stomodeeum) and hind-intestine (proctodaeum), la- brum ........... 547 Completion of the head 548 g. The appendages ........... 548 The cephalic appendages 548 The thoracic appendages ......... 550 The abdominal appendages 550 Appendages of the first abdominal segment (pleuropodia) . . 551 Are the abdominal legs of Lepidoptera and phytophagous Hymen- optera true limbs ?......... 552 The trachea? 553 h. Nervous system ........... 554 Completion of the definite form of the body ..... 555 i. Dorsal closure and involution of the embryonic membranes . . . 556 j. Formation of the germ-layers ........ 558 k. Farther development of the mesoderm ; formation of the body-cavity . 563 I. Formation of organs .......... 566 The nervous system .......... 566 Development of the brain ........ 567 Development of the eyes ......... 567 Intestinal canal and glands 569 The salivary glands .......... 570 The urinary tubes 572 The heart 572 The blood-corpuscles 574 Musculature ; connective tissue ; fat-body ..... 574 The reproductive organs ......... 575 Development of the male germinal glands ..... 579 m. Length of embryonic life 582 n. The process of hatching 583 The hatching spines . 585 xvi TEXT-BOOK OF ENTOMOLOGY PART III. THE METAMORPHOSES OF INSECTS PAGE a. The nymph as distinguished from the larval stage . . 593 b. Stages or stadia of metamorphosis . . . 594 c. Ametabolous and metabolous stages . . ... 594 THE LARVA -599 a. The Campodea-form type of larva ... . 600 b. The cruciform type of larva ... . . 602 c. Growth and increase in size of the larva .... . 608 d. The process of moulting .... . . 609 The number of moults in insects of different orders . . . 615 Reproduction of lost limbs .... . 619 Formation of the cocoon ... . 619 Sanitary conditions observed by the honey-bee larva, and admis- sion of air within the cocoon . 623 THE PUPA STATE .... • 625 a. The pupa considered in reference to its adaptation to its surround- ings and its relation to phylogeny . 631 b. Mode of escape of the pupa from its cocoon ... . 632 c. The cremaster • • 636 Mode of formation of the cremaster and suspension of the chrysalis in butterflies • 637 FORMATION OF THE PUPA AND IMAGO IN THE HOLOMETABOLOUS INSECTS (THE DIPTERA EXCEPTED) 641 a. The Lepidoptera ... The changes in the head and mouth-parts ... . 646 The change in the internal organs . . . 647 The wings 654 Development of the feet and of the cephalic appendages . . 654 Embryonic cells and the phagocytes . . . 655 Formation of the femur and of the tibia; transformation of the tarsus ... 656 The antennae • 657 Maxillse and labial palpi 658 Process of pupation b. The Hymenoptera ... . • Ocular or oculo-cephalic buds .... • 665 The antennal buds • 665 The buds of the buccal appendages 665 The buds of the ovipositor . ... . 665 DEVELOPMENT OF THE IMAGO IN THE DIPTERA . . • 606 a. Development of the outer body-form Formation of the imago in Corethra . Formation of the imago in Culex 670 TABLE OF CONTENTS xvii PAGE Formation of the imago in Chironomus 671 Formation of the imago in Muscidse 673 b. Development of the internal organs of the imago .... 678 The hypodermis 678 The muscles 680 The digestive canal 681 The tracheal system 683 The nervous system 684 The fat-body 685 Definitive fate of the leucocytes 685 The postembryonic changes and imaginal buds in the Pupipara (Melophagus) 686 c. General summary 687 HYPERMETAMORPHISM 688 SUMMARY OF THE FACTS AND SUGGESTIONS AS TO THE CAUSES OF META- MORPHISM 705 Theoretical conclusions ; causes of metamorphosis .... 708 TEXT-BOOK OF ENTOMOLOGY PAKT I. -MORPHOLOGY AND PHYSIOLOGY POSITION OF INSECTS IN THE ANIMAL KINGDOM ALTHOUGH the insects form but a single class of the animal king- dom, they are yet so numerous in orders, families, genera, and species, their habits and transformations are so full of instruction to the biologist, and they affect human interests in such a variety of ways, that they have always attracted more attention from students than any other class of animals, the number of entomologists greatly surpassing that of ornithologists, ichthyologists, or the special stu- dents of any other class, while the literature has assumed immense proportions. Insects form about four-fifths of the animal kingdom. There are about 250,000 species already named and contained in our museums, while the number of living and fossil species in all is estimated to amount to between one and two millions. In their structure insects are perhaps more complicated than any other animals. This is partly due to the serial arrangement of the segments and the consequent segmental repetition of organs, espe- cially of the external appendages, and of the muscles, the tracheae, and the nerves. The brain is nearly or quite as complicated as that of the higher vertebrates, while the sense-organs, especially those of touch, sight, and smell are, as a rule, far more numerous and only less complex than those of vertebrates. Moreover, in their psychical development, certain insects are equal, or even superior, to any other animals, except birds and mammals. The animal kingdom is primarily divided into two grand divisions, the one-celled (Protozoa) and many-celled animals (Metazod). In the latter group the cells and tissues forming the body are arranged in three fundamental cell-layers ; viz. the ectoderm or outer layer, the mesoderm, and endoderm. The series of branches, or phyla, com- B 1 2 TEXT-BOOK OF ENTOMOLOGY prised under the term Metazoa are the Porif era, Coelenterata, Vermes, Echinodermata, Mollusca, Arthropoda, and Vertebrata. Their ap- proximate relationships may be provisionally expressed by the fol- loAving TABULAR VIEW OF THE EIGHT BRANCHES OR PHYLA OF THE ANIMAL KINGDOM. VIII. Vertebrata. Ascidians and Fishes to Man. VII. Arthropoda. Trilobites, Crustacea, Arachnida, Insects, etc. VI. Mollusca. Clams, Snails, Cuttles. V. Echinodermata. Crinoids, Star-fish, Sea-urchins, etc. IV. Vermes. Flat and Round Worms, Polyzoa, Brachiopods, Annelids. III. Ccelenterata. Hydra, Jelly-fishes. II. Porifera. Sponges. METAZOA. Many-celled animals with 3 cell-layers. I. PROTOZOA. Single-celled animals. RELATIONS OF INSECTS TO OTHER ARTHROPODA The insects by general consent stand at the head of the Arthro- poda. Their bodies are quite as much complicated or specialized, and indeed, when we consider the winged forms, more so, than any other class of the branch, and besides this they have wings, fitting them for an aerial life. It is with little doiibt that to their power of flight, and thus of escaping the attacks of their creeping arthropod enemies, insects owe, so to speak, their success in life ; i.e. their numerical superiority in individuals, species, and genera. It is also apparently their power of moving or swimming swiftly from one place to another which has led to the numerical superiority in species of fishes to other Vertebrata. Among terrestrial vertebrates, the birds, by virtue of their ability to fly, greatly surpass in number of species the reptiles and mammals. The Arthropoda are in general characterized by having the body RELATIONS OF INSECTS TO OTHER ARTHROPODA 3 composed of segments (somites or arthromeres) bearing jointed ap- pendages. They differ from the worms in having segmented ap- pendages, i.e. antennae, jaws, and legs, instead of the soft unjointed outgrowths of the annelid worms. Moreover, their bodies are com- posed of a more or less definite number of segments or rings, grouped either into a head-thorax (cephalothorax) and hind-body, as in Crus- tacea, or into a head differentiated from the rest of the body (trunk), the latter not being divided into a distinct thorax and abdomen, as in Myriopoda; or into three usually quite distinct regions — the head, thorax, and hind-body or abdomen, as in insects. In certain aberrant, modified forms, as the Tardigrada, or the Pantopoda, and the mites, the body is not differentiated into such definite regions. In their internal organs arthropods agree in their general relations with the higher worms, hence most zoologists agree that they have directly originated from the annelid worms. The position and general shape of the digestive canal, of the nervous and circulatory systems, are the same in Arthropoda as in annelid (oligochete) worms, so much so that it is generally thought that the Arthropoda are the direct descendants of the worms. It is becoming evident, however, that there was no common ancestor of the Arthropoda as a whole, and that the group is a polyphyletic one. Hence, though a convenient group, it is a somewhat artificial one, and may eventually be dismembered into at least three or four phyla or branches. The following diagram may serve to show in a tentative way the relations of the classes of Arthropoda to each other, and also may be regarded as a provisional genealogical tree of the branch. 9. Insecta. 4. Arachnida. 3. Merostomata. 1. Crustacea. 2. Trilobita. I 7. Chilopoda. 6. Diplopoda. 8. Symphyla. 6a. Pauropoda. 4a. Pantopoda. b. Tardicjrada. 5. Peripatus. Different Annelida. Trochusiihwra. 4 TEXT-BOOK OF ENTOMOLOGY We will now rapidly review the leading features of the classes of Arthropoda. The Crustacea. — These Arthropoda are in many most important characteristics unlike the insects; they have two pairs of antennae, five pairs of buccal appendages, and they are branchiate Arthropoda. They have evidently originated entirely independently, and by a direct line of descent from some unknown annelid ancestor which was either a many-segmented worm, with parapodia, or the two groups together with the Rotifera may have originated from a com- mon appendigerous Trochosphaera. Their segments in the higher forms are definite in number (23 or 24) and arranged into two regions, a head-thorax (cephalothorax) and hind-body (abdomen). Nearly all the segments, both of the cephalothorax and abdomen, bear a pair of jointed limbs, and to them at their base are, in the higher forms, appended the gills (branchiae). The limbs are in the more specialized forms (shrimps and crabs) differentiated into eye- stalks, two pairs of antennae, a pair of palpus-bearing jaws (mandi- bles), two pairs of maxillae and three pairs of maxillipeds; these appendages being biramose, and the latter bearing gills attached to their basal joints. The legs are further differentiated into ambula- tory thoracic legs and into swimming or abdominal legs, and in the latter the first pair of the male is modified into copulatory organs (gonopoda). The male and female reproductive organs as a rule are in separate individuals, hermaphrodites being very unusual, and the glands may be paired or single. The sexual outlets are gener- ally paired, and, as in the male lobster and other Macrura, open in the basal joint of the last pair of legs, and in the female in the third from the last; while originally in all Crustacea the sexual organs were most probably paired (l^ig. 3, B}. They are, except a few land Isopoda, aquatic, mostly marine, and when they have a metamorphosis, pass through a six-legged larval stage, called the Nauplius, the shrimps and crabs passing through an additional stage, the Zoea. Crustacea also differ much from insects in the highly modified nature of the nephridia, which are usually represented by the green gland of the lobster, or the shell-glands of the Phyllopoda, which open out in one of the head-segments; also in 1,1 HI possession of a pair of large digestive glands, the so-called liver. Intermediate in some respects between the Crustacea and insects, but more primitive, in respect to what are perhaps the most weighty characters, than the Crustacea, are the Trilobita, the Merostomata (Limulus), and, finally, the Arachnida, these being allied groups. In the Trilobita and Merostomata (Limulus), the head-appendages are RELATIONS OF INSECTS TO OTHER ARTHROPODA more like feet than jaws, while they have in most respects a similar mode of embryonic development, the larval forms being also similar. The Merostomata. — The only living form, Limulus, is undoubtedly a very primitive type, as the genital glands and ducts are double, opening wide apart on the basal pair of abdominal legs (Fig. 3). Moreover, their head-appendages, which are single, with spines on the basal joint, are very primitive and morphologically nearer in shape to those of the worms (Syllidse, etc.) than even those of the Crustacea. Besides, their four pairs of coxal glands, with an external opening at the base of the fifth pair of head- appendages, and which probably are modified nephridia (Crustacea having but a single pair in any one form, either opening out on the second autennal, green gland, or second maxil- lary, shell-gland, seg- ment), indicate a closer approximation to the polynephrous worms. Limulus has other ar- chaic features, espe- cially as regards the structure of the simple and compound eyes and the simple nature of the brain. The Trilobita. — These archaic forms are still more generalized and primitive than the Merostomata and Crus- tacea, and probably were the first Arthropoda to be evolved from some unknown annelid worm. They had jointed biramose limbs of nearly uniform shape and size on each segment of the body, which were not, as in Crustacea, differentiated into antennae, jaws (man- dibles), maxillae, rnaxillipeds, and two kinds of legs (thoracic and FIG. 1. — Restoration of under side of a trilobite (Triar- thrux becff.i), the trunk limbs bearing small triangular respira- tory lobes or gills. — After Beecher. 6 TEXT-BOOK OF ENTOMOLOGY FIG. 2. — Restored section of Calymene : C, carapace: en, endopodite ; en', exopodite ; with the gills on the epipodal or respiratory part of the appendage. — After Walcott. abdominal), showing that they are a much more primitive type, and nearer to the annelids than any other Arthropoda. Their gills, as shown by the researches of Wal- cott and of Beecher, were at- tached to nearly if not every pair of limbs behind the antennae (Figs. 1, 2). The fact that in Trilobita the first pair of limbs is antenniform does not prove that they are Crustacea, since Eurypterus has a similar pair of appendages. The limbs in trilobites, as well as the abdominal ones of merostomes, and all those of Crustacea, except the first antennae, are biramose, consisting of an outer (exopo- dite) and an inner division (endopodite). In this respect the ter- restrial air-breathing tracheate forms, Arachnida, Myriopoda, and Insecta, differ from the branchiate forms, as their legs are single or undivided, being adapted for supporting the body during locomotion upon the solid earth. It is to be observed that when, as in Limulus, the body is supported by cephalic ambulatory limbs, they are single, while the abdominal limbs, used as they are in swimming, are biramose, much as in Crustacea. The Arachnida. — The scorpions and spiders are much less closely allied to the myriopods and insects than formerly supposed. Their embryology shows that they have descended from forms related to Limulus, possibly having had an origin in common with that animal, or having, as some authors claim, directly diverged from some primitive eurypteroid merostome. But they differ in essential respects, and not only in the nature and grouping of their appen- dages; the first pair instead of antenniform being like mandibles, and the second pair like the maxillae, with the palps, of insects, the four succeeding segments (thoracic) bearing each a pair of legs. They also have a brain quite unlike that of Limulus, the nervous cord behind the brain, however, being somewhat similar, though that of Limulus differs in being enveloped by an arterial coat. Arachnida respire by tracheae, besides book-lungs, which, however, are possibly derivatives of the book-gills of Limulus, while they perform the office of excretion by means of the malpighian tubes, and like Limulus possess two large digestive glands ("liver"). Their embryos have, on at least six abdominal segments, rudiments of limbs, three pairs of which form the spinnerets, showing their B 01) ..00 ed, FIG. 3. — Paired genital openings of different classes of arthropods. A, the most primitive, of Liinuluspolyphtm n\ : gen. p. generative papilla?; d, duet; »•//, vas deferens ; t, tendinous stigmata ; r-tii/. stigmata; e, external branchial muscle; ant, anterior lamellar muscle. — After Ben- ham, with a few changes. B, lobster (Ifomarus rulf/fn'ix), $ : of, genital aperture on 3d pair of legs; nr, ovary ; u, unpaired portion of tlie same ; i*>tii>m capenxix. Mi- view, enlarged about twice the natural si/e. — After Moseley. from Balfour. (' Anatomy of Per-ipatun capensis. The en- teric canal behind the pharynx has been re- moved, it, brain : n antenna ; n/>. oral or slime papilla-; .W. slime -hind; *•/•. slime reservoir, uhieli at UK- xime time- arts as a duet to the flland • xii., .s/),, .wn. .s".). nephridia of the 4th, r,th 6th, and 9th pairs of limbs ; a«, elongated eoxal ffland of the last pair of feet ; go. genital aperture; an, anus; pA, pharynx; n, longi- tudinal trunk of the nervous system. — After I'.alfour, from Lan-r. /*, Portion of the body ol Periprtlwt oanensin opened to show the scat- tered tufts ,,f trueliee (/tT. i\ '', ventral nerve -ds. - After Moseley. 10 RELATIONS OF INSECTS TO OTHER ARTHROPODA 11 originally derived from the setiparous glands in the appendages (parapodia) of annelid worms. The genital glands and ducts are paired, but it is to be observed that the outlets are single and situated at the end of the body. In the male the ejaculatory duct is single ; in its base a spermatophore is formed. It will be seen, then, that Peripatus is not only a com- posite type, and a connecting link between worms and tracheate arthropods, but that it may reasonably be regarded, if not itself the ancestor, as resembling the probable progenitor of myriopods FIG. 4. — E, Peripatus ed-icttfilnii, heart from the under side: a, base of antenna; op, oral papilla ; the figure also shows the papilliv around the mouth, and the four jaws. — After Balfonr, from Lang. F, Anterior end of Pf-ripuilis <'njie-nnin, ventral sick', laid open : n, antenna ; 2, tongue ; k, jaw : ml, salivary gland ; gn, union of the two salivary glands ; ph. pharynx ; tx, oesophagus ; /, lip pnpillii- around the mouth; op, oral or slime papilla ; aid, duct or reservoir of the slitne gland. — After Balfonr, from Lang. and insects, though of course there is a very wide gap between Peripatus and the other antennate, air-breathing Arthropoda. Relation of Myriopods to Insects. — The Myriopoda are the nearest allies of the insects. They have a distinct head, with one pair of antenna?. The eyes are simple, with the exception of a single genus (Cermatia), in which they are aggregated or compound. The trunk or body behind the head is, as a rule, long and slender, and com- posed of a large but variable number of segments, of equal size and shape, bearing jointed legs, which invariably end in a single claw. The mouth-parts of the myriopods are so different in shape and general function from those of insects, that this character, together with the equally segmented nature of the portion of the body behind the head (the trunk), forbids our merging them, as some have been 12 TEXT-BOOK OF ENTOMOLOGY dens - After Latzei.- inclined to do, with the insects. There are two sub-classes of myriopods, differing in such important respects that by Pocock l and by Kingsley they are regarded as independent classes, each equiva- lent to the insects. Of these the most primitive are the Diplopoda (Chilognatha), represented by the galley-worms (Julus, etc.). In the typical Diplopoda the head consists of three segments, a preoral or antennal, and two post- oral, there being two pairs of jaw-like appendages, which, though in a broad morphological sense homo- logues of the mandibles and first maxillae of insects, are quite unlike them in details. As we have previously stated,2 the so-called " mandibles " of diplopods are entirely different from those of insects, since they appear to be 2- 5. — Mandi or 3-jointed, the terminal joint being 2-lobed, thus resembling the maxillae rather than the mandibles of insects, which consist of but a single piece or ; m, muscle! joint, probably the homologue of the galea or molar joint of the diplopod protomala. The mandible of the Julidse (Fig. 5, Julus molybdinus), Lysiopetalidse, and Polydesmidae consists of three joints; viz. a basal piece or cardo, a stipes, and the mala mandibularis, which supports two lobes analogous to the galea and lacinia of the maxilla of an insect. There is an ap- proach, as we shall see, i-n the mandible of Copris, to that of T -i . -, i i. • tile dUllClya, L>Ut l l j-l l^^v, nfi'vi general tlie lacinia is wanting, ^1 flio TQ-iv f>nn«i. e, stipes exterior: with the „,.,,,,„„ ext,,n,,r <;„„/. e, and maieiia interior ("1"1 '>• ""' sti''es interior. with the nialiiU-lhi ; an(lth(. |ai,j(.||a (hypophurynx orv..m uatiu with its 1 Zool. Anzeiser, xvi, 1893, pp. 271-5. 2 On the morphology of the Myriopoda, Proc. Amer. Phil. Soc. 1883, pp. 197-209. RELATIONS OF INSECTS TO OTHER ARTHROPODA FIG. 7. — Deutomala of Julus, the lettering as in Fig. 6. known, judging by Metschnikoff's work on the embryology of the diplopods, these myriopods seem to have in the embryo but two pairs of post-antennal mouth-parts, which he designated as the "mandibles" and "labium." Meinert, however, regards as a third pair of mouth-parts or " labium " what in our Fig. 7 is called the internal stipes (stip. i.), behind which is a triangular plate, lamina labialis (lam. lab), which he re- gards as the sternite of the same seg- ment. The hypopharynx, our "labiella," (Fig. 6), with the supporting rods or stili linguales (sti. I), of Mein- ert, are of nearly the same shape as in some insects. Of the clypeus of insects there is apparently no homologue in myriopods, though in certain dip- lopods there is an interantennal clypeal region. The labium of insects is represented by a short, broad piece, which, however, unlike that of insects, is immovable, and is flanked by a separate piece called the epilabrum (Fig. 8). Vom Rath has observed an epipharynx, which has the same general relations as in insects. The embryology of myriopods is in many re- spects like that of insects. The larva of diplopods hatches with but few segments, and with but three pairs of limbs ; but these are not, as in insects, appended to consecutive segments, but in one species the third, and in another, Julus multi- striatus? (Fig. 10), the second, segment from the head is footless, while Vom Rath represents the first segment of an European Blaniulus as footless, the feet being situated consecutively on segments FIG. 9. — Larva of . m, . . Julus : a, the 3d ab- £ to 4. Ihe new segments arise at "the growing dominai segment, with • , ,, •, •, , ,, n , . . the new limbs just bud- point situated between the last and penultimate ding out; 6, new *eg- , • r /-VT , \ ments arising between Segment, growing Out 111 groups Of Sixes (Newport) the penultimate and the or in our Julus multistriatus? in fives (Fig. 10). In Stip" M 14 TEXT-BOOK OF ENTOMOLOGY adult life diplopods (Julus) have a single pair of limbs on the three first segments, or those corresponding to the thoracic segments of insects, the succeeding segments having two pairs to each seg- ment. Sinclair (Heathcote) regards each double segment in the. diplopods as not two original segments fused together, nor a single segment bearing two pairs of legs, but as " two complete segments perfect in all particulars, but united by a large dorsal plate which was origi- nally two plates which have been fused together." (Myriopods, 1895, p. 71.) That the segments were primitively separate is shown, he adds, by the double nature of the circulatory sys- tem, the nerve cord, and the first traces of segmentation in the mesoblast. Kenyon believes that from the con- ditions in pauropods, Lithobius, etc., there are indications of alternate plates (not segments) having disappeared, and of the remaining plates overgrow- ing the segments behind them, so as to give rise to the anomalous double segments.1 FIG. 10. — Freshly hatched larva of Julus multistriatus ? 3 mm. long: a, 5 pairs of rudi- mentary legs, one pair to a segment. Diplopods are also provided with eversible coxal sacs, in position like those of Symphyla and Synaptera; Meinert, Latzel, and also Haase having detected them in several species of Chor- deumidse, Lysiopetalidae, and Polyzonidse (Fig. 11). In Lysiopetalum anceps these blood-gills occur in both sexes between the coxae of the third to sixteenth pair of limbs. In the Diplopods the blood-gills appear to be more or less permanently everted, while in Scolopendrella they are usually retracted within the body (Fig. 15, eg). Diplopods also differ externally from in- sects in the genital armature, a complicated apparatus of male claspers and hooks apparently arising from the sternum of the sixth segment and being the modified seventh pair of legs. In myriopods i Morphology and class! ficatioii of the Pauropoda ; also American Naturalist, 1897, p. 410. FIG. 11. — Sixth pair of legs of Poli/eoninm gemnaniciMn, 9 : c.v, ventral sacs; cn.r, coxa; xt, sternal plate; .v, spirade. — After Haase. RELATIONS OF INSECTS TO OTHER ARTHROPOD A 15 there are no pleural pieces or " pleurites," so characteristic of winged insects. Perhaps the most fundamental difference between diplopods and insects is the fact that the paired genital openings of the former are situated not far behind the head between the second and third pair of legs. Both the oviducts and male ejaculatory ducts are paired, with separate openings. The genital glands lie beneath, while in chilopods they lie above the intestine; this, as Korschelt and Heider state, being a more primitive relation, since in Peripatus they also lie above the digestive canal. The nervous system of diplopods is not only remarkable for the lack of the tendency towards a fusion of the ganglia observable in insects, hut for the fact that the double segments are each provided with two ganglia. The brain also is very small in proportion to the ventral cord, the nervous system being in its general appearance somewhat as in caterpillars. The arrangement of the tracheae and stigmata is much as in insects, but in the Diplopoda the tracheary system is more primitive than in chilopods, a pair of stigmata and a pair of tracheal bundles occurring in each segment, while the bundles are not connected by anastomos- ing branches, branched tracheae only occurring in the Glomeridae. The tracheae themselves are without spiral threads (taenidia). It is noteworthy that the tracheae arise much later than in insects, not appearing until the animal is hatched; in this respect the myriopods approximate Peripatus. In the Chilopoda also the parts of the head, except the epicranium, are not homologous with those of insects, neither are the mouth- parts, of which there are five pairs. The structure of the head of centipedes is shown in part in Fig. 12, compare also Fig. 8. It will be seen that it differs much from that of the diplopods, though the mandibles (protomalae) are homolo- gous; they are divided into a cardo and stipes, thus being at least two-jointed. The second pair of postoral appendages is in centipedes very differ- ent from the gnathochilarium of diplopods. As seen in Fig. 12 -2, they are separate, cylindrical, fleshy, five-jointed appendages, the maxillary appendages of Newport, which are "connected trans- versely at their base with a pair of soft appendages " (c), the lingua of Newport. The third and fourth pair are foot-jaws, and we have called them malipedes, as they have of course no homology with the maxillipedes of Crustacea. The second pair of these malipedes, forming the last pair of mouth-appendages, is the poison-fangs (4), 16 TEXT-BOOK OF ENTOMOLOGY which are intermediate between the malipedes and the feet; Meinert does not allow that these are mouth-appendages. The embryology of Geophilus by Metschnikoff shows plainly the four pairs of post-antennal appendages. The embryo Geophilus is hatched in the form of the adult, having, unlike the diplopods, no metamorphosis, its embryological history being condensed or abbre- viated. But in examining Metschnikoff's figures certain primitive diplopod features are revealed. The body of the embryo shortly before hatching is cylindrical; the sternal region is much narrower than in the adult, hence the insertions of the feet are nearer together, while the first six pairs of appendages begin to grow out before the Fro. 12. — Structure of a chilopod. A, Lithobiiix americanus, natural size. B, tinder side of head and first two body-segments and less, enlarged : ant, antenna ; 1, jaws ; 2, first accessory jaw ; c, lingua; 3, second accessory jaw and palpus; 4, poison-jaw. (Kinysley del.) C, side view of head (after Newport) : ep, epiuranium ; I, frontal plate ; ac, scute ; 1, first leg ; &p, spiracle. hinder ones. Thus the first six pairs of appendages of the embryo Geophilus correspond to the antennae, two pairs of jaws, and three pairs of legs of the larval Julus. These features appear to indicate that the chilopods may be an offshoot from the diplopod stem. The acquisition of a second pair of legs to a segment in diplopods, as in the phyllopod Crustacea, is clearly enough a secondary character, as shown by the figures of Newport in his memoir on the develop- ment of the Myriopoda (PI. IV.). Thus the tendency in the Myriopoda, both diplopods and chilopods, is towards the multipli- cation of segments and the elongation of the body, while in insects the polypodous embryo has the three terminal segments of the RELATIONS OF INSECTS TO OTHER ARTHROPODA 17 abdomen well formed, these being, however, before hatching, partly atrophied, so that the body of insects after birth tends to become shortened or condensed. This indicates the descent of insects from ancestors with elongated polypodous hind-bodies like Scolopendrella. Korschelt and Heider suggest that the stem-form of myriopods was a homonomously jointed form like Peripatus, consisting of a rather large number of segments, but we might, with Haase, consider that the great number of segments which we now find indicates a late acquisition of this form. The genital opening in chilopods is single, and situated in the penultimate segment of the body, as in insects. While recognizing the close relationship of the Myriopoda with the insects, it still seems advisable not to unite them into a single group (as Oudemans, Lang, and others would do), but to regard them as forming an equivalent class. On the other hand, when we take into account the form and structure of the head, antennae, and especially the shape of the first pair of mouth-appendages, being at least two- jointed in both groups, we think these characters, with the homon- omously segmented body behind the head, outweigh the difference in the position of the genital outlet, important as that may seem. It should also be taken into account that while insects are derived from polypodous ancestors, no one supposes, with the exception of one or two authors, that these ancestors are the Myriopoda, the latter having evidently descended from a six-legged ancestor, quite differ- ent from that of the Campodea ancestor of insects.1 In regard to the sexual openings of worms, though their position is in general in the anterior part of the body, it is still very variable, though, in general, paired. In the oligochete worms the genital zone, with the external openings, is formed by the segments lying be- tween the 9th and 14th rings, though in some the genital organs are situated still nearer the head. The myriopods, which evolved from the worms earlier than insects, appear to have in their most primi- tive forms (the Diplopoda) retained this vermian position of the genital outlets. In the later forms, the chilopods, the genital open- ings have been carried back to near the end of the body, as in insects. From observations made by three different observers on the freshly hatched larva of the Julidfe, it appears that the an- cestral diplopods were six-footed, or oligopod, the larva of Pauropus 1 The term which we proposed for this hypothetical ancestor of insects, " Leptus- like " or " Leptiform," was an unfortunate one, since the name Leptus was originally given to the six-legged larva of a mite (Trombidinm), the origin of the mites and other Arachnida being entirely different from that of the myriupods and insects, c 18 TEXT-BOOK OF ENTOMOLOGY (Fig. 13) approaching nearest to our idea of the ancestral rnyriopod, which might provisionally be named Protopauropus. Relations of the Symphyla to Insects. — Opinions respecting the position of the Symphyla, represented by Scolopendrella (Fig. 14), are very discordant. By most writers since Newport, Scolopen- drella has been placed among the myrio- pods. The first author, however, to examine its internal anatomy was Menge (1851), who discovered among other structures (tracheae, Fio. 13. — Paurnpits huarleyi, much enlarged. A, enlarged view of head, antennne, and first pair of legs (original). /»', young. — After Lubboek. ("", longitudinal M-etion of Pauropus !/ i/f/ei/i,^ '. a, brain ; /', salivary gland; 1; mid-intestine ; (/, rei-tum; /(. ventral nervi'-oonl ; c, bud-like rem- nants of coxa- ; , rudiment of the palpus. — After Latzel. D, end of the body: pn, eleventh, />12. twelfth undeveloped pair of leenings opisthogoneate, usually single, but paired in Thysannra (Lepisma), Dermaptera, and Plectoptera (Ephemeridce). The digestive canal in the winged orders is highly differentiated, the fore-intestine being divided into an oesophagus and jiroroitricttlus, the hind-intestine into an ileum, colon, and rectum, with rectal glands. The neri'ous system consists of a well-developed brain, in the more specialized orders highly complicated; no more than thirteen pairs of ganglia, which may be more or less fused in the more specialized orders. Three frontal ganglia, and a well-developed, sympathetic system present. Stigmata confined (except possibly in Sminthurus) to the thorax and abdomen, not more than ten pairs in all, and usually but nine pairs. Tracheal system as a rule highly differentiated; invariably with tcenidia. Dorsal vessel with ostia and valvules; no arteries except the cephalic aorta; no veins. After birth there is in the more specialized pterygote orders a, reduction in the number of terminal segments of the abdomen. Development either direct (Synaptera), or with an incomplete (with nymph and /ringed or imaginal stages), or complete metamorphosis; in the latter case ivith a larval, pupal, und imago stage. The insects may be divided into two subclasses, --the Synaptera, and the winged orders, Pterygota, of Gegenbaur (1877), since the differences between the two groups appear on the whole to be of more than ordinal rank. 1. EXTERNAL ANATOMY a. The regions of the body The insects differ from other arthropods in that the body is divided into three distinct regions, — the head, thorax, and abdomen, the latter regions in certain generalized forms not always very distinctly differentiated. The body behind the head may also conveniently be called the trunk, and the segments composing it the trunk- segments. In insects the head is larger in proportion to the trunk than in other classes, notably the Crustacea; the thorax is usually slightly or somewhat larger than the head, while the hind-body or abdomen •2s TEXT-BOOK OF ENTOMOLOGY is much the larger region, as it consists of ten to eleven, and per- haps in the Dennaptera and Orthoptera twelve, segments, and con- tains the mid- and hind-intestine, as well as the reproductive organs. When we compare the body of an insect with that of a worm, in which the rings are distinctly developed, we see that in insects ring distinctions have given way to regional distinctions. The segments lose their individuality. It is comparatively easy to trace the seg- ments in the hind-body of an insect, as in this region they are least modified; so with the thorax; but in the head of the adult insect it is impossible to discover the primitive segments, as they are fused together into a sort of capsule, and have almost entirely lost their individuality. In general it may be said that the head contains or bears the organs of sense and of prehension and mastication of the food ; the thorax the organs of locomotion ; and the abdomen those of repro- duction. When we compare the body of a wasp or bee with that of a worm, we see that there is a decided transfer of parts headward; this pro- cess of cephalization so marked in the Crustacea likewise obtains in insects. Also the two hinder regions of the body are, in a much greater degree than in worms, governed by the brain, the principal seat of the intelligence, which, so to speak, dominates and unifies the functions of the body, both digestive, locomotive, and repro- ductive, as also those of the muscles moving the different segments and regions of the body. To a large extent arthropodan morphology and class distinctions are based on the regional arrangement of the somites themselves. Thus in the process of grouping of the seg- ments into the three regions, some increase in size, while others undergo a greater or less degree of reduction; one segment being developed at the expense of one or more adjoining ones. This principle was first pointed out by Audouin, and is called Audouin's law. It is owing to the greater development of certain segments and the reduction of others, both of the body-segments and of the segments of the limbs, that we have the wonderful diversity of form in Jthe species and genera, and higher groups of insects, as well as those of other arthropods. b. The integument (exoskeleton) The skin or integument of insects consists, primarily, as in worms and all arthropods, of an epithelial layer of cells called the Ji>//><>-
  • i-ini». This layer secretes the cuticle, which is of varying thick- THE INTEGUMENT 29 ness and flexibility, and is usually very dense, impermeable, and light, compared with the crust of the Crustacea, where the cuticle becomes heavy and solid by the deposition of the carbonate and phosphate of lime. This is due to the presence of a substance called by Odier chit in.1 The cuticle is thin, delicate, and flexible between the joints ; it is likewise so in such diaphanous aquatic larvae as that of Corethra, and in the gills of aquatic insects, also in the walls of the tracheae and of the salivary ducts. The cuticle thus forms a more or less solid crust which is broken into joints and pieces (sclerites), forming supports for the attachments of the muscles and serving to protect the soft parts within. Chitin. --If we allow an insect to soak for a long time in acids, or boil it in liquid potassa or caustic potash, the integument is not affected. The muscles and the other soft parts are dissolved, leav- ing the cuticle clear and transparent. This insolubility of the cuti- cle is due to the presence of chitin, the insoluble residue left after such treatment. It also resists boiling in acids, in any alkalies, alcohol or ether. The chemical formula is C^HogXoCV2 "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 organized form. The color which it frequently exhibits is not due to any essential ingredient ; it may be diminished or even destroyed by various bleaching processes." (Miall and Denny.) "The chemical stability of chitin is so remarkable that we might expect it to accumulate like the inorganic constituents of animal skeletons, and form perma- nent deposits. Schlossberger (Ann. d. chem. u. pharm., bd. 98) 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." (Miall and Denny, The Cockroach, p. 29.) Chitin, or a substance closely similar to it, occurs in worms and in their tubes, especially in the pharyngeal teeth of annelids and in their setae. The shell of Lingula and the pen of cuttle-fish contain true chitin (Krukenberg). The integu- ment of Liniulus, of trilobites, and of Araclmida, as well as Myriopoda, appears to consist of chitin.3 The chitin is rapidly deposited at the end of embryonic life, also during the larval and pupal stages. As is well known, insects after 1 Lassaigne gave it the name of entomoline. 2 Miall ami Denny ex Krukenberg; Kolbe gives the formula as CyH15N06 or CjgH^NOjo. As the result of his recent researches, Krawkow (Zeits. Biol., xxix, 1.S9L', p. 177) states that the chemical composition of chitin may prove to be some- what variable. 3 On allowing portions of a locust, a piece of the integument of Liniulus, a scorpion, and a myriopod to soak for a month in white potash, neither were dissolved or affected by the reagent. 30 TEXT-BOOK OF ENTOMOLOGY moulting are white, but in a few hours turn dark, and those which live in total darkness are white, showing that light has a direct effect in causing the dark color of the integument. Moseley analyzed one pound weight of Blatta, and found plenty of iron with a remarkable quantity of manganese. Schneider regarded chitin as a hardening of the protoplasm rather than a secretion, and the cuticle is looked upon as an exudation. It is structureless, not consisting of cells, and consists of fine irregular laminse. "A cross-section of the chitinous layer or ' cuticle' ex- amined with a high power shows extremely close and fine lines per- pendicular to the laminae." In the cockroach the free surface of the cuticle is divided into polygonal, raised spaces or areas which correspond each to a chitinous cell of the hypodermis. (Miall and Denny.) Numerous pore-canals pass through the cuticle of all the external parts of the body. The larger canals nearly always form the way for the passage of secretions from dermal cells, or connect with the cavities of hairs or setae ; when very fine and not connected with hairs or scales, they are either empty or filled with air, and may pos- sibly serve for respiration. Vosseler distinguishes in the cuticle two layers of different physi- cal and chemical characters. Besides the external chitinous layer there is an inner layer which entirely agrees with cellulose. (Zool. Centralblatt, ii, 1895, p. 117.) The reparative nature of chitin is seen in the fact that Verhoeff finds that a wound on an adult Carabus, and presumably on other insects, is speedily closed, not merely by a clot of blood, but by a new growth of chitin. c. Mechanical origin and structure of the segments (somites, arthromeres, metameres, zonites) The segments are merely thickenings of the skin connected by folds or duplications of the integument, and not actually separate or individual rings or segments. This is shown by longitudinal (sagit- tal) sections through the body, and also by soaking or boiling the entire insect in caustic potash, when it is seen that the integument is continuous and not actually subdivided into separate somites or nrthromeres, since they are seen to be connected by a thin inter- scgmental membrane (Tig. !<>)• But this segmentation or metame- rism of the integument is, however, the external indication of the segmentation of the arthropodan body most probably inherited MECHANICAL ORIGIN OF THE SEGMENTS 31 me" from the worms, being a disposition of the soft parts which is characteristic of the vermian type. This segmentation of the integu- ment is correlated with the serial repetition of the ganglia of the nervous system, of the ostia of the dorsal vessel, the primitive disposition of the segmental and reproduc- tive organs, of the soft, muscular dissepiments which correspond to the suture between the segments, and with the metameric arrangement of the muscles controlling the movements of the segments on each other, and which internal segmentation or meta- merism is indicated very early in embryonic life by the mesoblastic somites. In the un jointed worms, as Graber states, the body forms a single but flexible lever. In the earthworm the muscular tube or body-wall is enclosed by a stiffer FIG. 16. — Dia- cuticle, divided into segments ; hence the worm can ?™« of the anterior ... . part of an insect, move in all required directions, but only by sections, showing the membra- . nous intersegmental as seen in Fig. 16, which represents the thickened folds, g.— After Gra- bcr. integument divided into segments, and folded inward between each segment, this thin portion of the skin being the inter- segmental fold. Each segment corresponds to a special zone of the subdivided muscular tube (m), the fascia extending longitudinally. The figure shows the mode of attach- ment of the fascia of the muscle-tube to the seg- ment. The anterior edge is inserted on the stiff, un- yielding, inner surface of each segment : the hinder edge of the muscle is at- tached to the thin, flex- ible, intersegmental fold, which thus acts as a ten- don on which the muscle can exert its force. (Gra- ber.) " Fig. 17 makes this still clearer. The muscles (m) extend between two segments immediately succeeding each other. Supposing the anterior oue (^1) to be stationary, what do we then see when the muscle contracts ? Does it also become shorter ? The interseg- Fio. 17. — Diagram of the internment and arrangement of the segments! muscles: A, relaxed; m, muscle; g, membranous articulation ; r, chitinous ring. B, the same contracted on both sides. C, on one side. — After Graber. 32 TEXT-BOOK OF ENTOMOLOGY segmental again mental fold is drawn forwards, and hence the entire hinder segment moves forward and is shoved into the front one, and so on with the others, as at B. Afterwards, if the strain of the muscle is relieved by the diminishing action of the tensely stretched, inter- membrane, it returns to a state of rest." (Graber.) While we look upon the dermal tube of worms as a single but flexible lever, the body of the arthropods, as Graber states, is a linear system of stiff levers. We have here a series of stiff, solid rings, or hooks, united by the intersegmental mem- brane into a whole. When the muscles, extending from one ring to the next behind contract, and so on through the entire series, the rings approximate each other. The ectoskeletal segments bend to one side by the con- traction of the muscles on one side, the point of the outer segmental fold oppo- site the fixed point becoming converted into the turning- point (C). The usual result of the arrangement of the locomo- tive system is the simple curving of the body (C), and Fi<;. 18. — Diagrams to demonstrate the mechan- ism of the motion of the segmented body in the Arthropoda: One larger segment (cf) and 4 smaller. The exoskeleton is indicated by black lines, the inter- articular membranes by dotted lines. The hinurcs between consecutive segments are marked at, tergal (dorsal) skeleton; «, sternal (ventral) skeleton; d, dorsal longitudinal muscles = extensors (and flexors in an upward direction) ; »>. ventral longitudinal muscles = flexors. In /?, the row of segments is stretched ; in A, by the contraction of the musclcsU/) bent upward ; in (\ downward ; ty, tergal ; sy, sternal interarticnlar membranes. — After Lang. then the alternate bending of the body to right and left, which produces the serpentine movements characteristic of the earthworms, the centipede, and many insect larvae. The most strik- ing example of the wonderful variety of movements which can be made by an insect are those of the Syrphus larva. When feeding amid a herd of aphides, it is seen to now raise the front part of the MECHANICAL ORIGIN OF THE SEGMENTS 33 body erect aud stiff, then to bend it down, or rapidly turn it to either side, or move it in a complete circle. (Graber, pp. 23-20.) The arrangement and mode of working of the muscles, says Lang, is illustrated by Fig. 18, which shows us five segments, one larger (ct) and four smaller, in vertical projection. The thicker portion of the integument is marked by strong outlines, the delicate and flexible interarticular membranes (tg, sg~) in dotted lines. The hinges between* two consecutive segments are marked a. A dorsal muscle (d) is attached to the larger segment (cf), and runs through the smaller segments, being inserted in the dorsal portion of the crust (£) of each by means of a bundle of 'fibres. A ventral muscle (v) does the same on the sternal side (s). " The skeletal segments," adds Lang, " may be compared to a double-armed lever, whose fulcrum lies in the hinges. If the dorsal muscle contracts, it draws the dorsal arm of the lever (the tergal portion of the skeleton) in the direction of the pull towards the larger segments ; the tergal interarticular membranes become folded, the ventral stretched, and the four segments bend upward (Fig. 18, A). If the ventral muscle contracts, while at the same time the dorsal slackens, the row of segments will be bent downwards (Fig. 18, C)." L. B. Sharp suggests, that in the Crustacea the rings formed by " the regularity and stress of muscular action " would be hardened by the deposition of lime at the most prominent portion, -i.e. between what we have called the intersegmental folds. (American Naturalist, 1893, p. 89.) Cope also states that " with the beginning of indura- tion of the integument, segmentation would immediately appear, for the movements of the body and limbs would interrupt the deposit at such points as would experience the greatest flexure. The muscular system would initiate the process, since flexure depends on its con- tractions, and its presence in animals prior to the induration of the integuments in the order of phylogeny, furnishes the conditions re- quired." (The Primary Factors of Organic Evolution, p. 208, 1895.) It is apparent that the jointed or metameric structure of the bodies of insects and other arthropods is an inheritance from the segmented worms. In the worms the body is a continuous dermo- muscular tube, while in arthropods this tube is divided into regions, and the cuticle is thicker and more resistant. To go back to the incipient stages in the process of segmentation of the body, we con- ceive that the worms probably arose from a creeping gastrula-like form, the gastraea. The act of creeping gradually induced an elon- gated shape of the body. The movement of such an organism in a TEXT-BOOK IN ENTOMOLOGY forward direction would gradually evolve a fore and aft, dorsal and ventral, and bilateral symmetry. As soon as this was attained, as the effect of creeping over rough irregular surfaces there would result mechanical lateral strains intermittently acting during the serpentine movements of the worm. The integument would, we can readily suppose, tend to bend or yield, or become permanently wrinkled, at more or less regular intervals. The arrangement of the muscles would gradually conform to this habit of creeping, and finally the nervous system and other organs more directly con- nected with the creeping move- ments of the organism would tend to be correlated in their arrange- ment with that of the segments. In this way the homonomous seg- ments of the annelid body prob- ably became developed, and their relations and shapes were eventu- ally fixed by inheritance. After this stage was reached, and limbs began to appear, the segments would tend to become heterono- mous, and to be grouped into regions. The origin of the joints or seg- ments in the limbs of arthropods was probably due to the mechanical strains to which what were at first soft fleshy outgrowths along the sides of the body became sub- jected. Indeed, certain annelid worms of the family Syllidae have segmented tentacles and para- podia, as in Dujardinia (Fig. 19). We do not know enough about the habits of these worms to under- stand how this metamerism may have arisen, but it is possibly due to the act of pushing or repeated efforts to support the body while creeping over the bottom among broken shells, over coarse gravel, or among seaweeds. It is obvious, however, that the jointed structure of the limbs of arthropods, if we are to attempt any explanation at all of the origin of such structure, was primarily due mainly to lateral strains and FIG. 19. — Dujarrfinin rofifera, with jointed tt-ntarli's and caudal iipjuMulages. — With some changes, after Quatn-tages. MECHANICAL ORIGIN OF THE LIMBS 35 impacts resulting from the primitive endeavors of the ancestral arthropods to raise and to support the body while thus raised, and then to push or drag it forward by means of the soft, partially jointed, lateral limbs which were armed with bristles, hooks, or finally claws. On the other hand, by adaptation, or as the result of parasitism and consequent lack of active motion, the original number of segments may by disuse be diminished. Thus in adult wasps and bees, the last three or four abdominal segments may be nearly lost, though the larval number is ten. During metamorphosis the body is made over, and the number, shape, and structure of the segments greatly modified. In the female of the Stylopidse the thorax loses all traces of segments, and is fused with the head, and the abdominal segments are faintly marked, losing their chitin. While the maxillee have several joints, the mandibles are 1-jointed, but there are traces of two joints in Campodea, certain beetles, etc. In the antenna there is a great elasticity in respect to the num- ber of joints, which vary from one or two to a hundred or more. It is likewise so in the thoracic legs, where the number of tarsal joints varies from one to five ; also in the cercopoda, the number of joints varying from one or two to twelve or more. (I. Mechanical origin of the limbs and of their jointed structure We have already hinted at the mode of origin of the limbs of arthropods. Like the body or trunk, the limbs are chitinous dermo- muscular tubes, with a dense solid cuticle, and internal muscles, and were it not for their division at more or less regular intervals into segments, forming distinct sets of levers, set up by the strains in these tubular supports, there would be no power of varied motion. Even certain worms, as already stated, have their tentacles and parapodia, or certain appendages of their parapodia, more or less jointed, but there are no indications of claws or of any other hard chitinous armature at the extremity, and the skin is thin and soft. In the most simple though not the most primitive arthropods, such as the Tardigrades, whose body is not segmented, there are four pairs of short unjointed legs, ending each in two claws, which have probably arisen in response to the stimulus of pushing or dragging efforts. The legs of Peripatus are unjointed, and have a thin cuticle, but end in a pair of claws, which have evidently arisen as a supporting TEXT-BOOK OF ENTOMOLOGY FIG. 20. — A pro- thoracic leg of ( 'hirono- mus larva ; and pupa. FIG. 21. — A, larva of Ephydra califurnica : a, b, c, pupa. armature, the result of the act of moving or pulling the body over the uneven surface of the ground. There is good reason to suppose that such limbs arose from dyna- mical causes, similar to those exciting the formation of secondary adaptations such as are to be seen in the prop or supporting legs of certain dipterous larvse, as the single pair of Chironomus (Fig. 20) and Simulium, or the series of unjointed soft tubercles of Ephydra (Fig. 21), etc., which are armed with hooks and claws, and are thus adapted for dragging the insect through or over vegetation or along the ground. Now by frequent continuous use of such unjointed structures, the cuticle would tend to become hard, owing to the deposit of a greater amount of chitin between the folds of the skin, until finally the body being elongated and hornonomously segmented, the movements of walking or running would be regular and even, and we would have homonomously jointed legs like those of the trilobites, or of the most generalized Crustacea and of Myriopoda. In the most primitive arthropods, — and such we take it were on the whole the trilobites, rather than the Crustacea, — the limbs were of nearly the same shape, being long and slender and evenly jointed from and including the antenna?, to the last pair of limbs of the abdominal region. In these forms there appear to be, so far as we now know, no differentiation into mandibles, maxilla?, maxillipedes, and thoracic legs, or into gonopoda. The same lack of diversity of structure and function of the head-appendages has survived, with little change, in Limulus. In the trilobites (Fig. 1) none of the limbs have yet been found to end in claws or forceps ; being in this respect nearly as primitive as in the worms. Secondary adaptations have arisen in Limulus, the cephalic appendages being forcipated, adapted as supports to the body and for pushing it onward through the sand or mud, while the abdominal legs are broad and flat, adapted for swimming and bearing the broad gill-leaves. It is thus quite evident that we have three stages in the evolution of the arthropod an limb; i.e. 1, the syllid stage, of simple, jointed, soft, yielding appendages not used as true supports (Fig. 19) ; 2, the MECHANICAL ORIGIN OF THE LIMBS 37 trilobite stage, where they .are more solid, evenly jointed, but not end- ing in claws; and by their comparatively great numbers (as in the trilobite, Triarthrus) fully supporting the body on the bottom of the sea. In Limulus they are much fewer in number, thicker, and acting as firm supports, the cephalic limbs of use in creeping, and ending in solid claws. 3, The third stage is the long slender swimming head- appendages of the nauplius stage of Crustacea. As regards the evolution of limbs of terrestrial arthropods, we have the following stages : 1, the soft un jointed limbs of Tardi- grades, ending in two claws, and those of Peripatus, and the pseudo- or prop-legs of certain dipterous larvae; 2, finally the evolution of the long, solid, jointed limbs of Pauropus and other primitive myrio- pods, the legs forming solid, firm supports elevating the body, and enabling the insect to drag itself over the ground or to walk or run. When the body is elongated and many-segmented, the legs are neces- sarily numerous ; but when it is short, the legs become few in number, i.e. six, in the hexapodous young of myriopods and in insects, or eight in Araclmida. Whenever the legs are used for walking, i.e. to raise and support the body, they end in a solid point or in a pair of forceps or claws. On the other hand, as in phyllopods, where the legs are used mainly for swimming, they are unarmed and are soft and membranous, or, as in the limbs of the nauplius or zoea stage of crustaceans, end in a simple soft point, which often bears tactile setae. The tarsal joints are more numerous in order to give greater flexi- bility to the limb in seizing and grasping objects, both to drag the body forwards and to support it. Unlike those of the Crustacea, the limbs of insects are not primi- tively biramose, but single, the three-lobed first maxillae, and sec- ondarily bilobed second maxillae being the result of adaptation. Embryology on the whole proves the truth of this assumption ; the maxillae of both pairs are at first single buds, afterwards becoming lobed. All the appendages of the body, including the ovipositor or sting, are modified limbs, as shown by their embryological develop- ment. It is noticeable that in the crab, where the body is raised by the limbs above the bottom, it is much shorter and more cephalized than in the shrimps. Also in the simply walking and running spiders, the hind-body is shorter than in scorpions, while in the running and flying insects, such as the Cicindelidae, and in the swiftly flying flies and bees, there is a tendency to a shortening of the body, especially of the abdomen. The long body of the dragon-fly is an 38 TEXT-BOOK OF ENTOMOLOGY impediment to flight, but compensated for by the action of the large wings. The arthropodan linib is a compound leverage system. It is, says Graber, a lateral outgrowth of the trunk, which repeats in miniature that of the main trunk, its single series of joints or segments form- ing a jointed dermo-muscular tube. Yet the lateral appendages of an insect differ from the main trunk in two ways : (1) they taper to the end which bears the two claws, and (2) their segments are in the living animal arranged not in a straight line, but at different angles to each other. The basal joint turning on the trunk acts as the first of a whole series of levers. The second joint, however, is connected with the musculature of the first or basal joint, and thus each suc- ceeding joint is moved on the one preceding. Each lever, from the first to the last, is both an active and a passive instrument. (Graber.) While, however, as Graber states, the limbs possess their own sets of muscles and can move by the turning of the basal joint, the labor is very much facilitated, as is readily seen, by the trunk, though the latter has to a great extent delegated its locomotive function to the appendages, which again divide its labor among the separate joints. Graber then calls attention to the analogy of the mechanics of locomotion of insects to those of vertebrates. An insect's and a vertebrate's legs are constructed on the same general mechanical principles, the limbs of each forming a series of levers. Fig. 22, A, represents diagramniatically the knee joint of a verte- brate, and B that of an insect ; a, the femur or thigh, and 6, the tibia or shank. In the verte- brate the internally situ- ated bones are brought into close union and bend by means of a hinge-joint ; so also in the chitinous- skinned insect. The stiff dermal tube °* the insect acts as a ipvpr l,v mpov.0 nf fllp UJ +],;„ infprepmnpntnl m^m braiie (c) pushed in or telescoped in to the thigh joint, a special joint-capsule being super- fluous. The muscles are in general the same in both types; they form a circle. In both the shank is extended by the contraction of the upper muscles (c?) and is bent by the contraction of the lower FIR. 22. — Diagram of the knen-joint of a vertebrate (A) and an insect's limb (5) : a, upper ; 6, lower, shank, united :it A by a rapsular joint, at B by a folding joint ; . 3, ii, pp. 271-374, tab. 1, 1844.) Winslow, A. P : son. Om byggnaden af thorax hos Insekterna. Helsingborg, 1KG2, 1 PI., pp. 24. Packard, Alpheus Spring. Guide to the study of insects. 1860. Systematic position of the ( )rthoptera in relation to other insects. (Third report U. S. Knt, Commission, pp. 28G-345, 1883, Pis. xxiii-lxi.) Graber, Vitus. Die Insekten. 12°, pp. 403, 003, Munchen, 1877, many Figs. Huxley, Thomas Henry. A manual of the anatomy of invertebrated animals. 12°, pp. 397-451, Figs., London, 1877. LITERATURE ON THE EXTERNAL ANATOMY 41 Hammond, Arthur. Thorax of the blow-fly. (Journ. Linn. Soc., London, xv. Zool., 1880, pp. 31.) Brauer, Friedrich. Ueber das Segment me"diaire Latreille's. (Sitzb. d. k. Akad. d. Wissensch. Wien, 1882, pp. 218-241, 3 tab.) Systematisch-zoologische Studien. (Ibid., 1885, pp. 237-413.) Gosch, C. C. A. On Latreille's theory of " Le Segment me'diaire." (Xat. Tidsskrift (3), xiii, pp. 475-531, 1883.) Miall, L. C., and Denny, Alfred. The structure and life-history of the cockroach (Periplaneta orientalis). An introduction to the study of insects. 8°, pp. 224, London, 1886. Cheshire, Frank R. Bees and bee-keeping, i, Scientific, London, 1886, Pis. and Figs. Lang, Arnold. Text-book of comparative anatomy, i, pp. 426-508, 1891, many Figs. Kolbe, H. J. Einfiihrung in die Kenntniss der Insekten. 8°, pp. 709, 324 figs., Berlin, 1893. Sharp, David. The Cambridge natural history. Insecta, i, 8°, pp. 83-584, 1895, Figs. 47-371. Also the works of Bos, Chabrier, Cholodkovsky, Comstock, Dewitz, Eaton, Erichson, Gerstaecker, Girard, Grassi, Hagen, Haase, Kellogg, Knoch, Lacordaire, Latreille, Leuckart, Lendenfeld, Lowne, Lubbock, Mayer, Meinert, F. Miiller, Osten-Sacken, Pagenstecher, Reinhard, Schaurn, Schiodte, Scudder, J. B. Smith, Spinola, Stein, Weismann, Wood-Mason. 42 TEXT-BOOK OF ENTOMOLOGY THE HEAD AND ITS APPENDAGES a. The head While the head is originally composed of probably not less than six segments, these are in the adult insect fused together into a cap- sule or hard chitinous box, the ejricranitim, with no distinct traces of the primitive segments. The head contains the brain and accessory ganglia, the mouth or buccal cavity, also the air-sacs in many winged forms, and gives support to the external organs of sense, the antennae, and to the buccal appendages, the larger part of the interior being filled with the muscles moving these structures. The solid walls of the head serve as a lever or support for the attachment of these muscles, especially those of the mandibles. Thus there is a correlation between the large size of the mandibles of the soldier white ants and ants, the head being correspond- ingly large to accommodate the great mandibular muscles. The other extreme is seen in the larva of Necrophilus (Fig. 24), with its long slender neck and diminutive head. The clypeus. - - This is that part of the head situated in front of the epi- cranium, and anterior to the eyes, form- ing the roof of the posterior part of the mouth, and is, as embryology shows, probably a tergal sclerite. It varies greatly in shape and size in the different orders of insects. It is often divided into two parts, the clypeus posterior and cbjpeus anterior, or which may be desig- nated as the post- and «iit('-<-l>ip9, 74), and its inner side is lined with a soft membrane, usually provided with hairs and sense-papillae or cups, forming the epipharynx. The labrum is more or less deeply bilobed, especially in caterpil- lars and in adult Staphyli.nid.8e, and has been thought by some FIG. 24. — Presumed larva of Nem- optera (Neci'ojrfiiliiif aren. c/y, clypeus posterior; llir, labrum ; iml. iiiiiinlible ; nur, base of first maxilla ; m/i, its palpus ; m, mentum ; s/n, submentum ; plpr, palpifer ; lig, fused second maxilla' ; ant, antenna; occ, occiput. 48 TEXT-BOOK OF ENTOMOLOGY All the gulo-mental region of the head appears to represent the base of the second maxillae, and the question hence arises whether the submentum is not the homologue of the cardines of the first maxillae fused, and the»mentum that of the stipites of the latter also fused to- gether. If this should prove to be the case, the homologies between the two pairs of maxillae will be still closer than before supposed. Where the gula is differentiated, this repre- sents the basal piece of the second maxillae. In Figs. 28, 29, 30, and 31, these three pieces are clearly shown to belong to the second maxillary seg- ment. It is evident that these pieces or sclerites belong to the second angitxti- maxillary or labial segment of the head, as does the occiput, which F,o.23.-Headof i,ibr, under side of the labrum ; as, hypo- represent the tergo-pleural portion of pharyngeal chitinous support. the segment. Miall and Denny also regarded the submentum as the basal piece of the second maxillae. The occiput ( Fig. 29, B, C), as stated be- yond, is very rarely pres- ent as a sepa- rate piece; in the adult insect we have only ob served it in FIO.SO. — Tiead). He calls this segment the intercalary.1 Heymons (1895) designates it as the 1 We may add, while correcting the proofs of this book, that the important sum- mary, by Uzel, of his work on the embryology of Campodea appears in the Zoologi- scher Anzeiger for July 5, 1897. He observes that the premandibular segment in the embryo is very distinct, and that the two projections arising from it persist in the FIG. 34. — Embryo of Anu- rirta muritima: 1c. ttj>. mi- nute temporary appendage of the tritocerebral segment, the premandibular appendage ; at, antenna; md, mandible; ma-1, first maxilla ; ins2, second max- illa ; ]il-jfi, thoracic ; uj>1, uj>-. abdominal appendages ; an, anus. — A fter W heeler. 52 TEXT-BOOK OF ENTOMOLOGY pr.m. md--- mx- nw/ -- ,ant md mxf - Fio. 35. — Head of embryo of honey bee : B, a little later stage than A. jir.in, premandibular segment; cl, clypeus ; ant, an- tenna; md, mandible; i/.">). This is, we think, a mistaken view, as proved by the embryology of the Odonata and of Nematus. Our statements on this subject were first published in part in 1871, and more fully in the third Report, U. S. Ent. Commission, 1883, pp. 284, 285. We also stated that all the gular region of the head probably represents the base of the primi- tive second maxillae. TEXT-BOOK OF ENTOMOLOGY This postoral segment at first appears to be one of the thoracic segments, but is afterwards added to the head, though not until after birth, as it is still separate in the freshly hatched nymph (Fig. 4; see also Kolbe, p. 132, Fig. 59, sq. 5). A. Brandt's figure of C«l<>pten/x rirr/o (PL 2, Fig. 19) represents an embryo of a stage similar to ours, in which the postoral or sixth (labial) segment is quite separate from the rest of the head. The accompanying figure, copied from our memoir, also shows in a saw-fly larva (JYi?wa/^.s venlriroxiix) the relations of the labial or sixth segment to the rest of the head. The suture between the labial segment and the preoral part of the head disappears in adult life. From this sketch it would seem that the back part of the head, i.e. of the epicranium, may be made up in part of the tergite or pleurites of the mandibular segment, since the mandibular muscles are inserted on the roof of the head behind the eyes. It is this labial segment which in Cory- dalus evidently forms the occiput, and of which in most other insects there is no trace in larval or adult life, unless we except certain Orthoptera (Locusta), and the larva of the Dyticidae. The following table is designed to show the number and succession of the segments of the head, with their respective segments. TABULAR VIEW OF THE SEGMENTS, PIECES (SCLERITES), AND APPENDAGES OF THE HEAD NAME OF SEGMENT PIECES OR REGIONS OF THE HEAD-CAPSULE APPENDAGES, ETC. ,- p • w ^"* r-TrS ? £ - o 1. Ocellar (Protocere- bral). 2. Antennal (Deuto- cerebral). 3. Preinandibular, or intercalary (Tri- tocerebral). 4. Mandibular. 5. 1st Maxillary. G. 2d Maxillary, or labial. Epicranium, anterior re- gion with the clypeus, labrum, and epiphar- ynx. Epicranium, including the antennal sockets. Wanting in postembry- onic life, except in Campodea. Epicranium, behind the antennae, genre. Epicranium, hinder edge? Tentorium. Occiput. Compound and simple eyes (Ocelli). Antennae. Premandibular append- ages (in Campodea). Mandibles. 1st Maxillfe. 2d Maxillae or Labium. Post-gula, gula, sub- mentum, men turn, hy- popharynx (lin.mia, ligula), paraglossae, spinneret. COMPOSITION OF THE HEAD IN HYMENOPTERA 55 a The composition of the head in the Hymenoptera. --Ratzeburg stated in 1832 that the head in the adult Hymenoptera (Cynips, Hemiteles, and Formica) does not correspond to that of the larva, but is derived from the head and the first thoracic segment of the larva. West- wood and also G-oureau made less complete but similar observations, though Westwood afterwards changed his opinion, and the same view Avas maintained by Eeinhard. Our OAvn observations (as seen in Fig. .38) led us to suppose that this Avas a mistaken vieAv ; that the larval head, being too small to contain that of the semipupa, was simply pushed forward, as in caterpillars. Bugnion, however, re- affirms it in such a detailed Avay tint Ave reproduce his account. He maintains that the Arie\vs of Ratzeburg are exact and easy to verify in the chalcid genus Encyrtus, ex- cept, hoAvever, that Avliich concerns the ventral part and the posterior border of the prothoracic seg- ment. As the time of transformation ap- proaches, the head of the larva, he says, is depressed and soon concealed under the edge of the protho- racic segment; the latter elongates, becomes thicker and more con- vex, and Avithin can be seen the t\vo oculocephalic imaginal buds. The head of the perfect insect is derived not only from the head of the larva, but also from the portion of the prothoracic segment which is occupied by the buds, i.e. almost its entire dorsolateral face. But the hinder and ventral part of this segment (which contains the imaginal buds of the first pair of legs) takes no part in the forma- tion of the head ; these parts, according to Bugnion, towards the end of the larval period detaching themselves so as to become fused Avith the thorax and constitute the pronotum and the prosternuui. FIG. 38. — Larva (a) of a chalcid, about to pupate, with the head, including- the eyes and three ocelli, in the prothoracic seg- ment : I/, c, pupa. This mode of formation of the head may be observed still more easily in Rhodites, Heraiteles, and Microgaster, from the fact that their oculocephalic FIG. 39. FIG. 40. st* FIG. 41. ant Ir. u,r.t - FIG. .T.I. — Anterior half of larva of Encyrtus, ventral face, showing the upper (wins) and lower (leg) thoracic Imaginal buds: />. mouth; eh, chitinons arch ; (//, silk gland ; (/.brain; «, nervous cord ; it1, bud of fore, , eye bud ; c, stomach. FIG. 41. — older Kneyrtus larva, lateral view, showing the buds of the antenna1 (/), legs, and in', oesophagus : '/'•', '/a, huds of the genital aniiature; ./', rndiment of the sexual gland (ovary or testis) ; r, urinary tube ; /, intestine (rectum); n, anus. Fio. 42. — A still older larva, ready to transform. The imnginnl buds of the antenna?, eyes, wings, and Icjjs have become elongated ; letteringas in Fig. 41. — This and Figs. SU-41 after Bugnion. 56 THE ANTENNAE 57 buds are much more precocious, and that the eyes are charged with pigment at a period when the insect still preserves its larval form. "... I believe that this mode of formation of the head occurs in all Hyme- noptera with apodous lame, in this sense ; that a more or less considerable part of the first thoracic segment is always soldered to the head of the larva to con- stitute the head of the perfect insect. The arrangement of the nervous system is naturally in accord with this peculiarity of development, and the cephalic ganglia of the larva to which the ocular blastems later adapt themselves, are found not in the head, but in the succeeding segment (Figs. 39, 40, 41). "Relying on these facts, I maintain that the encroachment of the head on the prothorax is a consequence of the preponderance in size of the brain, and indicates the superiority of the Hymenoptera over other insects. ..." That the pronotum is derived from the larval prothoracic segment is proved by the fact that the first pair of stigmata becomes what authors call the "pro- thoracic" stigmata of the perfect insect. But Bugnion thinks that the projec- tion which carries it, and which he calls the shoulder (Figs. 41 and 42), belongs to the mesonotum. b. Appendages of the head The antennae. — These are organs of tactile sense, but also bear olfactory, and in some cases auditory organs ; they are usually in- serted between or in front of the eyes, and moved by two small muscles at the base, within the head. In the more generalized insects the antenme are simple, many-jointed appendages, the joints being equal in size and shape. The antennae articulate with the head by a ball and socket joint, the part on which it moves being called the tornlns (Fig. 32, ?•). In the more specialized forms it is divided into the scape, the pedicel, and a fwjcUum (or clavola) ; but usually, as in ants, wasps, and bees, there are two parts, the basal three-jointed one being the scape, and the distal one, the usually long filiform flagellum. The antennae, especially the flagellum, vary greatly in form in insects of different families and orders, this varia- tion being the result of adaptation to their peculiar surroundings and habits. The number of antennal joints may be one (Articerus, a clavigerid beetle), or two in Paussus and in Art ran es cn'cus (Fig. 431-), where they are short and club-shaped ; in flies (Museidse, etc.), they are very short and with few joints, and when at rest lying in a cavity adapted for their reception. In the lamellicorn beetles the flagellum is divided into several leaves, and this condition may be approached in the serrate or flabellicorn antennae of other beetles. In Lepi- doptera, and in certain saw-flies and beetles, they are either pecti- nate or bipectinate, being in one case at least, that of the Australian Hepialid (Abantfartes argentens), tripectinate (Fig. 44), and in the dipterous (Tachinid) genus Talarocera the third joint is bipectinate (Fig. 45). In Xenos and in Parnus they may be deeply forked, 58 TEXT-BOOK OF ENTOMOLOGY while in Otiocerus, two long processes arise from the base, giving it a trificl shape. In dragon-flies and cicadae, they are minute and hair-like, though jointed, while in the larvae of many metabolous FIG. 43. — Different forms of antennas of beetles : 1, serrate ; 2, pectinate ; 3, capitate (and also geniculate) ; 4-7. clavate ; 8, 9, lamellate ; 10, serrate (Dorcatoma) ; 11, Irregular (Gyrinus) ; 12. two- join teli rinntoriux. — After Kolbe. insects they are reduced to minute three-jointed tubercles. In aquatic beetles, bugs, etc., the antennae are short, and often, when at rest, bent close to the body, as long antennae would impede their progress. While usually more or less sensorial in function, Graber states that the longicorn beetles in walking along a slender twig use their antennae as a rope- dancer does his balancing pole. Recent examination of the sense-organs in the antennae of an ant, wasp, or bee enables us, he says, to realize what wonderful or- gans the antennae are. In such insects we have a rod-like tube which can be folded up or extended out FIG. 44. — Tripec- . antenna ..i an into space, containing Australian moth. the antenna! nerve, FIG. 45. — Antenna uf TnJarocera iii- tix, J1. — After Williston. which arises din-rtly from the brain and sends a branch to each of the thousands of olfactory pits or pegs which stud its surface. The antenna is thus a wonderfully complex organ, and the insect must THE MANDIBLES 59 be far more sensitive to movements of the air, to odors, wave-sounds, and light-waves, than any of the vertebrate animals. That ants appear to communicate with each other, apparently talking with their antennae, shows the highly sensitive nature of these appendages. " The honey-bee when constructing its cells as- certains their proper direction and size by means of the extremities of these organs." (Newport.) How dependent insects are upon their antennae is seen when we cut them off. The insect is at once seriously affected, its central nervous system receiving a great shock, while it gives no such sign of distress and loss of mental power when we remove the palpi or legs. On depriving a bee of its antennae, it falls helpless and par- tially paralyzed to the earth, is unable at first to walk, but on partly recovering the use of its limbs, it still has lost the power of coordi- nating its movements, nor can it sting ; in a few minutes, however, it becomes able to feebly walk a few steps, but it remains over an hour nearly motionless. Other insects after similar treatment are not so deeply affected, though bees, wasps, ants, moths, certain beetles, and dragon-flies are at first more or less stunned and confused. The antennae afford salient secondary sexual differences, as seen in the broadly pectinated antennae of male bombycine moths, certain saw-flies (Lophyrus), and many other insects. The mouth-parts, buccal appendages, or trophi, comprise, besides the labrum, the mandibles and maxillae. The mandibles. — These are true jaws, adapted for cutting, tearing, or crushing the food, or for defence, while in the bees they are used as tools for modelling in wax, and in Cetonia, etc., as a brush for collecting pollen. They are usually opposed to each other at the tips, but in many carnivorous forms their tips cross each other like shears. They are situated below the clypeus on each side, and are hinged to the head by a true ginglymus articulation, consisting of two condyles or tubercles to which muscles are attached, the prin- cipal ones being the flexor and great extensor (Fig. 48). They are solid, chitinous, of .varied shapes, and in the form of the teeth those of the same pair differ somewhat from each other (Fig. 46 A). In the pollen-eating beetles (Cetoniae) and in the dung-beetles (Aphodius, etc.) the edge is soft and flexible. In the males of Lucanus, etc. (Fig. 47), and of Corydalus (Fig. 29), they are of colossal size, and are large and sabre-shaped in the larvse of water-beetles, ant-lions, Chrysopa, etc. where they are perforated at the tips, through which the blood of their prey is sucked. While the mandibles are generally regarded as composed of a TEXT-BOOK OF ENTOMOLOGY single piece, in Campodea and Macliilis there appears to be an additional basal piece apparently corresponding to the stipes of the A A> B C Fio. 46. — Various forms of mandibles. A, right and left of Tennopsis. A' showing- at the shaded portion the " molar " of Smith. £, Termesjla ripen, soldier ; md, its mandible. C', Panorpa. first maxilla, and separated by a faint suture from the molar or distal joint. In Cainpodea there is a minute movable appendage figured both by Meinert and by Nassonow, which appears to represent the lacinia of the maxilla (Fig. 48). Wood-Mason has observed in the mandibles of the embryo of a Javanese cockroach, Bkttta (Panesthki) Jamaica, indi- cations of "the same number of joints as in that of chilognathous myriopods, or one less than in that of Macliilis." Also he adds : "In both 'larvae' and adults of Panesthia jacanica a faint groove crosses the ' back ' of A Fir,. 48. — Mandible of Cainpodea: I, prostheea or lacinia; Fro. 47. — CMasognatlvitS g, cnlea; ./',/, tlexnr muscles; <% extensor; /•, r, retractor ; rt, gntntii, reduced. Mule. — mnsole retaining the mandible in its place. — After Meinert. A, After Darwin. extremity of the same. — After Nassonovv. the mandible at the base. This groove appears to be the remains of the joint between the third and apical segments of the formerly 4-segmented mandibles." MORPHOLOGY OF THE MANDIBLES 61 He also refers to the prostheca of Kirby and Spence (Fig. 49), which he thinks appears to be a mandibular lacinia homologous with it in Staphylinidae and other beetles (J. B. Smith also considers it as - homologous to the lacinia of the maxilla "), and on examining it in P. cornatus and a Nicaragua species (Fig. 49), we adopt his view, since we have found that it is freely movable and attached by a tendon and muscle to the galea. In the rove beetles (Goerius, Staphy- liiius, etc.) and in the subaquatic Heteroceridae, instead of a molar process, 'is a membranous setose appendage not unlike the coxal appendages of Scolopendrella, movably articulated to the jaw, which, he thinks answers to the molar branch of the jaws in Blatta and Machilis. " It has its homologue in the diminutive Trichoptery- gidte in the firmly chitinized quadrant-shaped sec- ond mandibular joint, which is used in a peculiar manner in crushing the food " ; also in the movable tooth of the Passalidae, and in the membranous inner lobe of the mandibles of the goliath-beetles, etc. J. B. Smith has clearly shown that the mandibles are compound in certain of the lamellicorns. In Copris Carolina (Fig. 50), he says, the small m embranous mandibles are divided into a basal piece (basal is), the homologue of the stipes in the maxilla ; another of the basal pieces he calls the molar, and this is the equivalent of the subgalea, while a third sclerite, only observed in Copris, is the conjitnctivns, the lacinia (prostheca) being well developed. Smith therefore con- cludes " that the structure of the mandible is fundamentally the same as that of the labium and maxilla, and that we have an equally complex organ in point of origin. Its usual function, however, demands a powerful and solid structure, and the sclerites are in most instances as thoroughly chitinized and so closely united to the others that practically there is only a single piece, in which the hoinology is obscured." (Trans. Amer. Ent. Soc., xix, pp. 84, 85. 1892.) From the studies of Smith and our observations on Staphy- linus, Passalus, Phanaeus, etc. (Fig. 50, A, B) we fully agree with the view that the mandibles are primarily 3-lobed appendages like the maxillae. Kyniphal Ephemerids have a lacinia-like process. (Heymons.) Fio. 49. — Mandible of Pusxalus cornutus with the prostheca (!) : A, that of a Nioaraguan species; a, inside, &, outside view, with the muscle. 62 TEXT-BOOK OF ENTOMOLOGY Mandibles are wanting in the adults of the more specialized Lepi- doptera, being vestigial in the most generalized forms (certain Tineina and Crambus), but well developed in that very primitive moth, Eriocephala (Fig. 51). They are also completely atrophied in the adult Trichoptera, though very large and functional in the pupa of these insects (Fig. 52), as also in the pupa of Micropteryx (Fig. 53). Fio. 50. — Mandible of C«prw carol! n«.— After Smith. A'C. licus. 4 (figure to right), do. of Leixluti-ojihiin cttir/ii/attm; £, of Phanatua carnifeJ-; (/', end of galea, — g, eularged; c, conjunctivas. C, of Meloe anguslicollis : I, lacinia; a, lacinia enlarged. They are also wanting in the imago of male Diptera and in the females of all flies except Culicidse and Tabanidse. They are said by Dr. Horn to be absent in the adult Plalupsyllus r,/.s/o/-/,s, though well developed in the larva; and functional mandi- bles arc lacking in the Hemiptera. The first maxillae. — These highly differentiated appendages are inserted on the sides of the head just behind the mandibles and the mouth, and are divided into three lobes, or divisions, which are sup- ported upon two, and sometimes three basal pieces, i.e. the basal THE FIRST MAXILLA 63 joint or cardo, the second joint or stipes, with the palpi fer, the latter present in Termitidae (Fig. 54, plpyr), but not always separately de- veloped (Fig. 55). The cardo varies in shape, but is more or less tri- angular and is usually wedged in between the submentum and mandi- ble. It is succeeded by the stipes, which usually forms the support for the three lobes of the maxilla, and is more or FIG. 52. — A, pupa of Ipcq cninrp in clirmp Phrygnnea pilosa.—M- Squai ter Pictet. B, mandibles rj-fae three distal divi- of pupa oi afolanna iingii- stftta.- After Sharp. sjolls of the maxilla ai'6 called, respectively, beginning with the in- nermost, the lacinia, galea, and palpifer, the latter be- ing a lobe or segment bearing the palpus. The lacinia is more or less jaw-like and armed on the inner edge with either flexible or stiff bristles, spines, or teeth, which are very variable in shape and are of use mx p FIG. 51.— Mandible of Erio- cep/xil, Axcti/njifnin loi/iji- •> i ,, i ., ic rp cornix. C, Myrineleoii divemum. Lettering as iu Fig. 54. THE FIRST MAX1LL.E 65 duced. In the Mecoptera the lacinia and galea are closely similar (Fig. 58) ; in the Trichoptera only one of the lobes is pres- ent (Fig. 59), while in Lepidoptera the galea unites with its mate to form the so-called tongue (Fig. 60). The maxilla of the male of Tegeticula yuccasella is normal, though the galese are separate ; but in the female, what Smith regards as the palpifer (the " tentacle " of Riley) is FIG. 56. — Maxilla of a carabM, AiwiiMhafmux tellkam}>fii : f, la- cinia; y, 2 -jointed galea; p, palpus; st, stipes ; 'c, cardo. Fio. 5S. — Mnx- illa of Panorpa. FIG. 57. — Maxilla of Nemognatha, ?, from Montana. A, base of maxilla enlarged to show the taste-pajiilla^ (t/>) and cups (7c), on the galea (t/n). B, jiart of end of tralea to .show the imperfect segments and taste-organs : H., nerve ; agangiionated nerve supplies each taste-papilla or cup ; I, lacinia ; />, palpifer ; «, subgalea. Fio. 59. — Maxilla of Lii/nirji/ti/tix /in- ttifiis: HIJ-, stipes; luc, galea. 66 TEXT-BOOK OF ENTOMOLOGY remarkably developed, being nearly as long as the galea (Fig. 6.1) and armed with stout setae, the pair of processes being adapted for holding a large mass of pollen under the head. In coleopterous larvae the niaxillse are 2-lobed FIG. 60. — Tonsnie of A It1i(l vyJina, with the end magnified. — Perg-ande del., from lcy. J, much reduced maxilla (ITIJC) of Paleacrita vernala ; mx.p, palpus. A FIG. fil. — .4, mnxilla of T«jitif>ihi yuceaseUa, or cheek- As already \( V J T observed, the second maxillae ap- pear to be the appendages of the last or occipital segment of the head. The second maxillae are very much differenti- ated and vary greatly in the different orders, being especially modified in the haustellate or suctorial orders, notably the Hymenoptera and Diptera. In the mandibulate orders, particularly the Orthoptera, where they are most generalized and primitive in shape and structure, they consist of the following parts : the gula (a post-gula is present in Dermap- tera), submentum (lora of Cheshire, i, p. 91), men- turn, palpifer, the latter bearing the palpi; the lingua (I i gula) and paraglossce, while the hypo- pharynx or lingua is situated on the upper side. The labial palpi are of the same general shape as those of the first maxillae, but shorter, with very rarely more than three joints, though in Ptero- narcys there are four. Leon has detected vestigial labial palpi in several Hemiptera (Fig. 73). As to the exact nature and limits of the gula, we are not certain ; it is not always present, and may ,;.'m be only a differentiation of the submentum, or the ^;_^ardo.- After latter piece may be regarded as a part of the gula. We are disposed to consider the second maxillae as morphologically nearly the exact equivalents of the first pair of maxillae, and if we Fm. f4. — Maxilla ol 3ms • MORPHOLOGY OF THE SECOND M AXILLAE 69 adopt this view it will greatly simplify our conception of the real nature of this complicated organ. The object of the fusion of the basal portion appears to be to form an under-lip, in order both to prevent the food from falling backwards out of the mouth, and, with the aid of the first pair of maxillae, to pass it forward to be crushed between the mandibles, the two sets of appendages acting somewhat as the tongue of vertebrates to carry and arrange or press the mor- sels of. food between the teeth or cutting edges of the mandibles. The spines often present on the free inner edges of the first and second maxillae (Figs. 54, 62) form rude combs which seem to clean the antennae, etc., often aiding the tibial combs in this operation. The submentum and mentum, or the mentum when no submentum is differentiated (with the gula, when present), appear to be collec- tively homologous with the cardines of the first pair of maxillae, to- gether with the palpifers and the stipites.1 These pieces are more or less square, and have a slightly marked median suture in Termitidae, the sign of primitive fusion or coalescence. The most primitive form of the second maxillae occurs in the Or- thoptera and in the Termitidae. The palpifer is either single (Peri- planeta, Diapheromera, Gryllidae) or double (Blatta orientalis, Locusti- dae). In Prisopus the single piece in front of the palpifer is in other forms divided, each half (Blatta, Locustidae, Acrydidae) bearing the two " paraglossae," which appendages in reality are the homologues of the lacinia and galea of the first maxillae.2 In the Termitidae (Fig. 65) the lingua is not differentiated from the palpifer, and the two paraglossae (or the lamina externa and interim of some authors) with the palpus are easily seen to be the homologues of the three lobes of the first maxillae. In the Perlidae (Pteronarcys, Fig. 66) the palpifer is divided, while the four paraglossae arise, as in Priso- pus and Anisomorpha, from an undivided piece, the lingua not being visible from without. In the Neuroptera the lingua or ligula is a large, broad, single lobe, without " paraglossae," and the palpifer is either single (Myrmeleon, Fig. 67), or divided (Mantispa, Fig. 68). 1 After we had arrived at this conclusion, and written the above lines, we received the Zoologischer Anzeiger for March 29, 1897, in which Dr. N. Le'ou publishes the same view, stating that each side of the subraentum is the homologue of the cardo, and each side of the mentum corresponds to the stipes of a single maxilla (p. 74) 2 Miall and Denny were the first to homologize the paraglossa; with the galea and laciuia, showing the complete resemblance of the second maxillae to the first pair, remarking that " the homology of the labium with the first pair of maxillae is in no other insects so distinct as in the Orthoptera." We have also independently arrived at a similar conclusion, but believe that the mentum corresponds to the first max- illary cardo, and the palpifer to the first maxillary stipes, the sclerite of each maxilla being fused to form the base of the labium, i.e. the unpaired mentum submentum. 70 TEXT-BOOK OF ENTOMOLOGY m In Corydalus (Fig. 29) the palpifer forms a single piece, and the lingua is undivided, though lobed on the free edge. In the metabolic orders above the Neuroptera the lingua is vari- ously modified, or specialized, with no vestiges of the lacinia or galea, except in that very primitive moth, Eriocephala, in which Walter found a minute free galea, me, and an inner lobe (Figs. 76, 77), the lacinia. The hypopharynx. — While in its most generalized condition, as in Synaptera, Derniaptera, Orthoptera, and Neurop- tera, this anterior median fold or out- growth of the labium forming the floor of the mouth may retain the designation of " tongue," lingua, or ligula ; in its more specialized form, particularly when used as a piercing or lapping organ, the use of the name hypopharynx seems most desirable. And this is especially the case since, like the epipharynx, it is morphologically a median structure, and while the epipharynx forms the soft, sensitive roof of the mouth, or pharynx ; Fio. 65. — Second maxillae of Ter- •, •, ,, , mopsis angusticoiiix: u, the homo- its opposite, the hypopharynx, rises as a fold from the floor of the mouth, form- ing in its most generalized condition a specialized fold of the buccal integument. In certain cases, as in the honey-bee, the very long li FIG 60. — Second maxillH' of Pteroniin-yx at// funned. Fio. 67. — Second maxilla? of Myrmeleon diversion. FK;. 68. — Second maxilkt' of Jf) of Duges (1832), the lingua of Westwood (Class, ins., ii, p. 489, 1840), " the unpaired median piercing organ " (" the analogon of the epi- pharynx of Diptera") of Karsten (18G4), the "tongue" of Taschen- berg (1880). The name hypopharynx was first proposed by Savigny in 1816, who, after naming the membranous plate which has for its base the upper side of the pharynx, the epipharynx, remarks : " Dans quelques genres, notamment dans les Euceres, le bord inferieur de ce meme pharynx donne naissance a un autre appendice plus solide que le precedent, et qui s'emboite avec lui. Je donnerai a ce dernier le nom de langue ou d' hypopharynx. Voila done la bouche des Hyme- nopteres composee de quatre organes impaires, sans y comprendre la ganache ou le menton ; savoir, la levre superieure, 1'epipharynx, 1'hypopharynx, et la levre inferieure, et de deux organes paires, les mandibules et les machoires." As stated by Dimmock : " The hypopharynx is usually present in Diptera (according to Menzbier absent in Sargus), and contains a tube, opening by a channel on its upper surface ; this channel extends back, more or less, from the tip, and is the outlet for the salivary secretion. The tip of the hypopharynx may be naked and used as a lance (Haematopota, according to Menzbier), or may be hairy (Musca). The upper side of the base of the hypopharynx is continuous with the lower wall of the pharynx ; its under surface may entirely coalesce with the labium (Culex, male), may join the labium more or less, anterior to the month (Musca), or, if TEXT-BOOK OF ENTOMOLOGY oc cither mandibles or maxillaa are present, its base may join them (Culex, female)." (p. 43.) We will now briefly describe the lingua, first of the mandibnlate or biting insects, and then its specialized form, the hypopharynx of the haustellate and lapping insects. The lingua (hypopharynx) exists in perhaps its most generalized condition in the Thysanura (Fig. 69), where it forms a soft projection, having the same relations as in Anabrns and other Or- thoptera.1 In the cockroach (Fig. 70), as stated by Miall and Denny, the lingua is a chitinous fold of the oral integument situated in front of the labiuni, and ly- ing in the cavity of the mouth. The common duct of the salivary glands Ibr rnx. Fir,, ra.- section of head of Ma- enters the lingua, and opens on its chili* iiKii-itiiint : In/p, hypopharynx; hinder snrflPP Thp lincmn iqqnrmnrtprl I1>,-, labnnn; t, tentorium ; ph, room Liace. .ngua IS SUppOUl in which the mandibles move on each l-,v a phitinnnc cVplpfrm fTTio-o 70 R • Q9 other ; /,, para-lossa ; m;r , labium • DJ c * 1SS- ( U> -° > <^5 .«/, salivary duct; x.ffl, salivary pland. o/irA « Thp thin fhitinnnq Qiirfqpp nf thp oe, uesophagus. - After Oudeuians. ^ *• ' lingua is hairy, like other parts of the month, and stiffened by special chitinous rods or bands." (Miall and Denny.) In the Acrydiidse (Melanoplus femur-rubrum) the tongue is a large, c B O FIG. 70. —Hypopharynx of Periplaneta orien- tufix; the arrow points out of the opening of tin- salivary duct: A, origin of salivary duct. B, side view. V, front view. — After Miall and Denny. membranous, partly hollow expansion of the base of the labium. It may be exposed by depressing the end of the labium, when the opening of the salivary duct may be seen at the bottom or end of the space or gap between the hinder base of the tongue, and the inner anterior base of the labium, as shown by the arrows in Fig. 70. It is somewhat pyriform, slightly keeled above, and bearing fine stiff bristles, which, as they point more or less inwards, probably aid in retaining the food within the mouth. The 1 Uzel states that what is regarderl as the ligula of Campodea is formed from the strniite of the first maxillary segment ; while t ho two parts regarded as paraglossaj grow out from the. slcrnite of the mandihular segment, and these three structures together he regards as the hypopharynx. (/ool. Auzeiger, July 5, 1897, p. 234.) THE H YPOPPIA R YNX 73 mxf.p nit FIG. 71. — Section through the anterior part of the head of Ana- brus (the mandibles removed), showing the relations of the hypo- pharynx (hi/I*} to the opening- of base of the tongue is narrow, and extends back to near the pharynx, there being on the floor of the mouth, behind the tongue, two oblique, slight ridges, covered with stiff, golden-yellow hairs, like those on the tongue. The opening of the salivary duct is situated on the under or hinder side of the hypopharynx, between it and the base of the labium, the base of the former being cleft ; the hollow thus formed is situated over the opening, and forms the salivary receptacle. In the Locustidae (Anabrus, Fig. 71) the tongue (hypopharynx) is a broad, some- what flattened lobe arising from the upper part of the base of the mentum and behind the palpifer. This lobe is cavernous un- derneath, the hollow being the salivary receptacle (sr) ; the latter is situated over the opening of the salivary duct, which is .... 1 " the salivary duct (sd)'. ff, galea ; placed between the base of both the hypo- /, lacinia; -/w, mentum ; o«, o?»opha- ... „.. .. gus ; Ibr, labrum ; /":/< >"'"'«»;/'- >t-!/;>,,-!/>t/ttittt. c, of Gerri* najas: hypopharynx is a very large, ml. mentum; li>, labial palpi; sg, subgalea; I, V1 a , ,-. lacinia (=intermaxillare and pnemaxillare of tongUC-llke, fleshy Outgrowth, and is, both in situation and structure, since it contains the opening of the silk-duct, exact- ly homologous with the hypo- pharynx of in- sects of other orders, being somewhat inter- mediate between the fleshy tongue or lingua of the man- dibulate insects, especially the Brulle) ; g, galea. — After Leon. br mt FIG. 74. — Section through head of a carabid, Anrtfithalmun telknmpfii : lir, brain ; /. g, frontal .«/<>. subu-sopliafreal prantrlion ; co, commissure; n. I, nerve seinlinu' branches to the i/i; in n. maxillary nerve; n/.r, 1st maxilla; mm, maxillary muscle; m.r', '.'d maxilla; ////. muscle of mentum ; If, elevator muscle of th sopliairus ; I of the clypeiis, nrxl a third beyond r.'iisintr the labrum (Ibr) ; fph, epipharynx ; (/, g , salivary glands above; fl-, lingual gland In-low the oesophagus (oe) ; m, mouth; pr, proventflculus ; md, mandible. A, section passing through lingual gland (f/2). THE HYPOPHARYXX 75 Neuroptera, and the hypopharynx of the bees (Fig. 80). Lucas describes and figures it under the name of " haustellum," but does FIG. 75. — Head of Analofia furcata : A, front view, >lio\ving the labrum removed. 5, side view ; ant, antenna ; oe, ocellus ; ol, labrum ; gh, articulatory process ; cw/a'j, cardo ; xtin&i, stipes ; lemaii, outer lobe tgalea) ; jifnta-i, palpus of 1st maxilla ; jit, palpus of 2d maxilla ; tut. haustellum ; «o, gustatory pits ; .s/»', opening of salivary duct ; chinp, chitinous hook of the clasp ; apr, furrow or gutter ol the haustellum. — After Lucas. not homologize it with the hypopharynx. The caddis-flies have been observed to drink water and take in both fluid and fine particles of solid food, and to use the haustellum for this purpose, the end being pro- vided with minute sense-organs like those on the first maxillary lacinia, and possibly of a gustatory nature. The spinneret of the larvae of Lepi- doptera is evidently the homologue of the hypopharynx of insects of other orders. It will be seen that the homol- ogy of the different parts is identical, the common duct of the silk-glands opening at the end of the hypo- pharynx, which here forms a complete tube or proboscis extending beyond the end of the labium, in adaptation to its use as a spinning organ. Walter refers to Burgess's discovery of a hypopharynx in Danais archippus, FIG. 7fi. — Hypopharynx of Erio- cepltala ch, pharynx; cor, cornea. — After Burgess. THE IIYPOPIIARYNX 77 In the fleas the hypopharynx is a large, slender, unpaired, long, chitinous trough, as long as the mandibles, and toothed at the end. Figures 79 and 80 show its relations to the other parts of the mouth ; in Fig. 79, a1, is seen where the salivary duct opens into the pharynx. Although this organ is not unanimously referred to the hypopharynx, B mx mx.p FIG. 79. — A, hypopharynx of Pulex canis : a;, basal portion situated within the head ; g. . the >aii- pharynx forms the receptacle or receptaculum, provided vary , orifice ol the' clnct ; x/i/i, styles of the hvpopharyiix ; inji/i, mem- hnmoiis eh, pharynx; p/i.m, pharyngeal muscle; p.pfi, protractor muscle of the pharynx; r.oe, retractor muscle of the oesophagus; r.ph, retractor muscle of the pharynx ; f.»e, flexor muscle of the pharynx ; (.of, twisting muscle of the oesophagus ; s.r, receptacle of the salivary duct ; I, its eleva- tor muscle ; s, its retractor muscle ; cl, clypeus. — After Meinert. scribed by Cheshire in his Bees and Bee Keeping.1 He calls it the tongue or ligula. It is situated in a tube formed by the maxillae and labial palpi, and can be partially retracted into the mentum. He states that it can move up and doAvn in the tube thus formed, oe s.d FIG. 84. — Oesophagus (oe), pharynx (ph) with epipharynx and labrura (Ibr) of AxUus ati-i- capilliis : HI, fih, pharyngeal muscle ; sr, salivary receptacle ; t, twisting ; /•, I' >, retractor muscles ; other lettering as in Fig. 83. — After Meinert. and then describes it as covered by a hairy sheath, its great elasticity being due to a rod running through its centre enabling it to be used as a lapping tongue. The sheath 1 See, also, Breithaupt, Ueber die Anatomie und die Functionen der Bienenzunge, 1886. It confirms and extends Cheshire's work. 80 TEXT-BOOK OF ENTOMOLOGY "passes round the tongue to the back, where its edges do not meet, but are continuous with a very thin plaited membrane ( (T, pm) covered with minute hairs. This membrane, after passing towards the sides of the tongue, returns to the angle of the nucleus, or rod, over the under surface of which it is probably con- tinued. The rod passes through the tongue from end to end, gradually tapering towards its extremity, and is best studied iu the queen, where I trace many nerve threads and cells. It is undoubtedly en- dowed with voluntary movement, and must be partly muscular, although I have failed completely in getting any evidence of stria- tion. The rod on the under side has a gutter, or trough-like hollow (r(?, the central duct) which is formed into a pseudotube (false tube) by intercrossing of black hairs. It will also be seen that, by the posterior meeting of the sheath, the space between the folded membrane (Cr, sd) be- comes two pseudotubes of larger size, which I shall call the side ducts. "These central and side ducts run down to that part of the tongue where the spoon, or bonton (A", Fig. 86) is placed. This is pro- vide d with very delicate split hairs (ft, Fig. 86) capable of brushing up the most minute quan- tity of nectar, which by capillarity is at once FIG. 65. — Head of honey bee, worker: ft, antenna; rj. epi- pharvnx ; in, mandible; //'.''. maxilla; IHJ'JI, maxillary palpus; /if/, paragloSSa ; ///, labial palpus; /, hvpopbarviix ; b, its spoon. — After Cheshire; from Hull. Div. Ent. V. S. Dep't. A^r. transferred by the gath- ering hairs (which are here numerous, long, and thin) to two side groove-like forms at the back of the bouton, and which are really the opened-out extremity of the centre and side duds, assuming, immediately above the bouton, the form seen in F, Fig. H6. The central duct, which is only from ^i.() inch to r-ltlnT, inch in diameter, because of its smaller size, and so greater capillary attraction, receives the nectar, if insufficient in quantity to fill the side ducts. But good honey-yielding plants would bring both centre and side ducts into requisition. The nectar is sucked up until it reaches the paraglossse (pa, B, Fig. 86), which are plate-like in front, but membranous THE HYPOPHARYNX 81 FIG. 86. — Tonq-ue or liarnla of the honey bee: A, under side of the tongue; 7;>, labial palpi; r, r, rod ; j>. pouch ; «//, sheath ; git, gathering hairs ; //, boiiton or spoon. B, under lip or labium, with appendages, partly dissected ; /, lora or siibmentum ; a, a, retractor lingme longus ; ml, salivary duct ; >•/> and l>, retractor lingua- biceps ; -1,1.1; maxilla' ; lj>, labial palpi ; pit. paragloBsa ; ;//'. feeding groove ; */(, sheath of ligula. C, D, E. sections of ligula ; hj>. hyaline plate of maxilla ; //, hairs acting as stops; in.r, maxilla; fj>, labial pal[ii ; .W, side duct, ^cross-section of extremity of tuuiMie near the "spoon" ; th, tactile hairs ; r, rod; 1>, nucleus; yh, patherins: hairs. G. cross-section of tongue without gathering hairs, x 4HO times; ah, shcalli; 1>, blood sjiac-e ; /. trachea: ;/;/. gustatory nerve; cil, central duct; ad, lateral duct; jnn. plaited membrane. //, same as (?, but magnified two hundred times, and with jitn. plaited membrane, turned outwards ; //. closiii'r hairs ; //<. labial palpi ; l>, blood ; ti, nucleus; r, rod ; h, closing hairs. /, small portion of the sheath ; lettering as before. K, extremity of the tongue, with spoon ; b, branching hairs for gathering. — After Cheshire. 82 TEXT-BOOK OF ENTOMOLOGY extensions, like small aprons, behind ; and by these the nectar reaches the front of the tongue, to be swallowed as before described." Cheshire then settles the question which has been in dispute since the time of Swammerdam, whether the bee's tongue is solid or tubu- lar. He agrees with Wolff that the duct is a trough and not a tube, and proves it by a satisfactory experiment. He remarks : "Bees have the power, by driving blood into the tongue, of forcing the rod out from the sheath, and distending the wrinkled membrane so that in section it appears as at H, Fig. 86, the membrane assuming the form of a pouch, given ant br 06 FIG. 87. —Longitudinal section through the head of the honey bee, 9. just outside of rip-lit an- tenna: in/t, antenna with three muscles attached to mes, mesocephalic pillar; cl, clypeus ; Ibr, lahruin ; 1, chyle-gland (system no. 1, of Siebold) ; o, opening of the same; oc, ocellus ; ///•, brain ; n, neck ; th, thorax ; oe, (esophagus ; .v.rf2, s.d3, common salivary ducts of systems ~2 and '.', ; /•, sali- vary valve ; c, cardo ; ph, pharynx ; mx', labium ; mx. 'p, labial palpi ; mt, mentum ; mx, maxilla ; >, hypopharynx ; s, boutou. — After Cheshire. in full length at A. It will be seen at once that this disposition of parts abol- ishes the side ducts, but brings the central duct to the external surface. The object of this curious capability on the part of the bee is, in my opinion, to permit of cleaning away any pollen grains, or other impediment that may collect in the side ducts. The membrane is greasy in nature, and substances or fluids can be removed from it as easily as water from polished metal. If, now, the sides of a needle, previously dipped into clove oil in which rosanilin (magenta) has been dissolved, so as to stain it strongly red, be touched on the centre of the rod, the oil immediately enters, and passes rapidly upwards and downwards, filling the trough." Does the hypopharynx represent a distinct segment? — The facts which suggest that the hypopharynx may possibly represent a highly modified pair of appendages, arising from a distinct intermaxillary segment, are these : Ileymons plainly shows that, in the embryo of Lepisma, the hypopharynx originates as a transverse sc^mcnt-likr fold in front of the 2d maxillary segment, and larger than it, and though he does not mention it in his text, it appears like the rudi- ment of a distinct segment ; the hypopharynx of Ephemerida; arises and remains separate in the nymph from the labium (see Ileymons' Fig. 29, and there are two lateral projections; see also Fig. 72, and Vayssiere's view that it may represent a pair of appendages ; Kolbo also regards it as representing a third pair of maxillte, his endolabium, p. 213). Though what is called an unpaired LITERATURE OF THE MOUTH-PARTS 83 organ, it is composed of, or supported by, two bilaterally symmetrical styles, both in Myriopods (Fig. 6, labiella, stil) and in insects (Fig. 77, etc.). On tin- other hand, in the embryo of pterygote insects, an intermaxillary segment has not been yet detected. LITERATURE OF THE MOUTH-PARTS OR BUCCAL APPENDAGES a. General Savigny, Jules-Cesar. Me"moires sur les animaux sans vertfebres. lre Part. Description et classification des animaux invert£br6s et article's, etc. Fasc. lre. Mein. 1-2. Th^oriedes organesde la bouche des crustaces et des insectcs. 12 PL, Paris, 1816, pp. 1-117. Gerstfeld, Georg. Ueber die Mundteile der saugenden Insekten. Dorpat, 1853. Olfers, Ernestus V. Anuotationes ad anatomiam Podurarum. Berolini, 1862, 4 Pis. Gerstaecker, Carl Eduard Adolph. Zur Morphologic der Orthoptera amphi- biotica. (Festschrift zur Feier des hundertjahrigen Bestehrns der Gesell- schaft naturf. Freunde zu Berlin. 4°, 1873, pp. 3U-59, 1 Taf.) Muhr, Joseph. Die Mundteile der Orthoptera. Em Beitrag zur vergleichenden Anatomie. (Jahrbuch "Lotos." Prag, 1877, pp. 40-71, 8 Tat'.) Burgess, Edward. The anatomy of the head and the structure of the maxilla in the Psocidae. (Proc. Boston Soc. Nat. Hist., xix, 1878, pp. 291-2C6, 1 PL) Meinert, Fr. Sur la conformation de la tete et sur 1' interpretation des organes buccaux chez les insectes, ainsi que sur la systematique de cette ordre. (Ent. Tidsskr., 1. Arg., 1880, pp. 147-150.) Tungens udskydelighed hos Steninerne, en slaegt af Staphylinernes familie. (Vidensk. meddel. fra den naturh. Foren, 1884-1886, pp. 180-207, 2 Pis. Also Zool. Anzeiger, 1887, pp. 136-139.) Muller, A. Vergleichend-anatomische Darstellung der Mundteile der Insekten. Villaeh, 1881, 3 Taf. Kraepelin, Karl. Ueber die Mundwerkzeuge der saugenden Insekten. (Zool. Anzeiger, 1882, pp. 574-579.) Dewitz, H. Ueber die fiihrung an den Korperanhangen der Insekten. (Berlin. Zeitschr. xxvi., 1882, pp. 51-68, Figs.) Wolter, Max. Die Mundbildung der Orthopteren mit specieller Beriicksichti- gung der Ephemeriden. 4 Taf. Greifswald, 1883. Oudemans, J. T. Beitrage zur Kenntniss der Thysanura und Collembola. (Hijilragen tot de Dierkunde, pp. 149-226. Amsterdam, 1888, 3 Taf.) Smith, John B. An essay on the development of the mouth-parts of certain insects. (Trans. Amer. Philosophical Soc., xix, pp. 175-198, 3 Pis.) Also articles by Chatin, McLachlan, Riley, Wood-Mason. b. Thysanoptera (Physapoda) Jordan, Karl. Anatomie und biologic der Physapoda. (Zeitschr. f. wissens. Zool., xlvii, pp. 541-620, 3 Taf. 1888.) Garman, H. The mouth-parts of the Thysanoptera. (Bull. Essex lust., xxii, 4 pp., Fig. 1890.) The asymmetry of the rnouth-parts of Thysanoptera. (Amer. Naturalist, July, 1896, pp. 591-593, Fig.) Bohls. J. Die Mundwerkzeuge der Physapoden. Dissertation Gottingen, 1891, pp. 1-36. 84 TEXT-BOOK ON ENTOMOLOGY Uzel, Heinrich. Monographic der Ordnuug Thysanoptera. Koniggratz, 1895, pp. -172, 10 Taf., 9 Figs. c. Hemiptera L6on, N. Beitrage zur Kenntniss der Munclteile der Hemipteren. Jena, 1887, pp. 47, 1 Taf. Labialtaster bei Hemipteren. (Zool. Anzeiger, pp. 145-147, 1892, 1 Fig.) Beitrage zur Kenntniss des Labiuuis der Hydrocoren. (Zool. Anzeiger, Marz 29, 1897, pp. 73-77, Figs. 1-5.) Geise, 0. Mundteile der Rhynchoten. (Archiv f. Naturgesch., xlix, 1883, pp. :; 15-373, 1 Taf.) Wedde, Hermann. Beitrage zur Kenntniss des Rhynchotenriissels. (Archiv f. Naturgesch., li Jahrg., 1 Bel., 1885, pp. 113-148, 2 Taf.) Smith, John B. The structure of the hemipterous mouth. (Science, April 1, 1892, pp. 189-190, Figs. 1-5.) d. Coleoptera Smith, John B. The mouth-parts of Copris Carolina ; with notes on the homolo- gies of the mandibles. (Trans. Amer. Ent. Soc., xix, April, 1892, pp. 83- 87, 2 Pis.) e. Lepidoptera Kirbach, P. Ueber die Mundwerkzeuge der Schmetterlinge. (Zool. Anzeiger, vi Jahrg., 1883, pp. 553-558, 2 Figs.) Ueber die Mundwerkzeuge der Schmetterlinge. (Archiv f. Naturge- schichte, 1884, pp. 78-119, 2 Taf.) Walter, Alfred. Palpus niaxillaris Lepidopterorum. (Jenaische Zeitschr. f. Naturwiss, xviii, 1884, pp. 121-173, Taf.) Beitrage zur Morphologic der Lepidoptera. I, Mundteile. (Jenaische Zeitschr. f. Naturwiss, xviii, 1885, pp. 751-807, 2 Taf.) Breitenbach, W. Vorlaufige Mitteilung tiber einige neue Untersuchungen an Bchmetterlingsrusseln. (Archiv f. mikroskop. Anatomie, xiv, 1877, pp. 308-317, 1 Taf.) Untersuchungen an Schinetterlingsriisseln. (Ibid., xv, 1878, pp. 8-29, ITaf.) Ueber Schmetterlingsriissel. (Entomolog. Nachr. 5 Jahrg., 1879, pp. 237-243, 1 Taf.) Der Schinetterliugsrtissel. (Jenaische Zeitschr. f. Naturwiss, 1881.) /. Siphonaptera Krapelin, K. Ueber die systematische Stellung der Puliciden. (Festschrift z. 50 jahr. Jubil. d. Realgymnas. lohanneum, Hamburg, pp. 17, 1 Taf. 1884.) Kellogg, V. L. The mouth-parts of the Lepidoptera. (Amer. Nat., xxix, 1895, pp. 540-556, 1 PI. and Fig.) g. Diptera Menzbier, Michael Alexander. Ueber das Kopfskelett und die Mundwerkzeuge der Zweiniigler. (Bull. Soc. Imp. Natur. de Moscou, lv, 1880, pp. 8-71, 2 Taf.) Dimmock, George. The anatomy of the mouth-parts and of the sucking appara- tus of some Diptera. Boston, 1881, pp. 48, 4 Pis. LITERATURE OF THE MOUTH-PARTS 85 Meinert, F. Fluernes Munddele. Trophi Dipterorum. Kjobenhavn, 1881, 6 Pis. Die Mundteile der Dipteren. (Zool. Anz. 1882, pp. 570-574, 599-003.) Becher, E. Zur Kenntniss der Mundteile der Dipteren. (Denkschr. Akad. d. Wissensch. Wien., xlv, 1882, pp. 123-162, 4 Taf.) Hansen, H. J. Fabrica oris dipterorum : Dipterernes mund : anatomisk og syste- matisk henseende. 1 Tabanidae, Bombyliidae, Asilidae, Thereva, Mydas, Apiocera. (Naturhist. Tidsskrift, 1883, xiv, pp. 1-18(3, Taf. 1-5.) Krapelin, Karl. Zur Anatomie und Physiologie des Riissels von Musca. (Zeitschr. f. wissensch. Zool., xxxix, 1883, pp. 683-719, 2 Taf.) McCloskie, George. Kraepelin's Proboscis of the house-fly. (American Natur- alisf, xviii, 1884, pp. 1234-1244, Figs.) Langhoffer, August. Beitrage zur Kenntniss der Mundtheile der Dipteren. Jena, 1888, pp. 1-32. Smith, John B. A contribution toward a knowledge of the mouth-parts of the Diptera. (Trans. Amer. Ent. Soc., xvii, Nov. 1890, pp. 319-339, Figs. 1-22. ) h. Hymenoptera Briant, Travers J. On the anatomy and functions of the tongue of the honey- bee (worker). (Journ. Linn. Soc., London, xvii, 1884, pp. 408-416, 2 Pis.) Breithaupt, P. F. Ueber die Anatomie und die Funktionen der Bienenzunge. (Archiv f. Naturgesch., Jahrg. Hi, 1886, pp. 47-112, 2 Taf.) i. Larval stages Brauer, F. Die Zweifliigler des kaiserlichen Museums zu Wien. Ill, Systema- tische Studien auf Grundlage der Dipterenlarven nebst einer Zusammenstel- lung von Beispielen aus der Litteratur uber dieselben und Beschreibung neuer Formen. (Denkschr. math.-naturwiss. Cl. k. Akad. Wiss. Wien, 1883, xlvii, pp. 100, 5 Taf.) Dewitz, H. Ueber die Fiihrung an den Korperanhangen der Insekten speziell betrachtet an der Legescheide der Acridier, dem Stachel der Meliponem und den Mundteilen der Larve von Myrmeleon, nebst Beschreibung dieser Organe. (Berliner ent. Zeitschr., xxvi, 1882, pp. 51-68.) Die Mundteile der Larve von Myrmeleon. (Sitzungsber. d. Ges. natur- forsch. Freunde zu Berlin, 1881, pp. 163-166.) Redtenbacher, Josef. Uebersicht der Myrmeleonidenlarven. (Denkschrift. math.-naturwiss. Cl. k. Akad. Wiss. Wien, 1884, xlviii, pp. 335-368, 7 Taf.) Schiodte, J. G. Ue metamorphosi Eleutheratorum. Bidrag til insekternes udviklingshistorie. (Kroyer's Naturhist. Tidsskrift. Kjobenhavn. 12 Teile mit 88 Taf., 1862-1883.) j. Embryonic stages Heymons, Richard. Grundziige der Entwicklung und des Korpersbaues von Odonaten und Ephemeriden. (Anhang zu den Abhandl. K. Akad. d. Wissens. Berlin, 1896, p. 22, 2 Taf. See Figs. 5, 29.) Entwicklungsgeschichtliche Untersuchungen an Lppisma saccharina L. (Zeitschr. f. wissens. Zoologie, Ixii, 1897, p. 595, 2 Taf. See Fig. 10.) TEXT-BOOK OF ENTOMOLOGY THE THORAX AND ITS APPENDAGES a. The thorax; it3 external anatomy The middle region of the body is called the thorax, and in general consists of three segments, which are respectively named the protho- rax, mesothorax, and metathorax (Figs. 88, 89, 98). FIG. 88. — External anatomy otJHelanoplun xjiretun, thi- head and thorax disjointed. The thorax contains the muscles of flight and those of the legs, besides the fore intestine (oesophagus and proventriculus), as well as, in the winged insects, the salivary glands. EXTERNAL ANATOMY OF THE THORAX 87 3 O O. CD In the more gener- alized orders, notably the Orthoptera, the three segments are distinct and readily identified. Each segment con- sists of the tergum, pleurum, and sternum. In the prothorax these pieces are not sub- divided, except the pleural ; in such case the tergum is called the pronotum. The prothorax is very large in the Orthop- tera and other gener- alized forms, as also in the Coleoptera, but small and reduced in the Diptera and Hy- menoptera. In the winged forms the tergum of the meso- thorax is differenti- ated into four pieces or plates (sclerites). These pieces were named by Audouin, passing from before backwards, the prca- scutum, scutum, scutel- lum,&u: tr, trochanters. A, tergal view of the mesothorax of the same ; j»'m, prieseutum ; m*, scu- tum ; scm, scutellum ; ptm, postscutellum ; t, tegula. form the base of attachment. The scutum is invariably present, as is the scutellum. The former in nearly all insects constitutes the larger part of the tergum, while the latter is, as its name implies, the small shield-shaped piece directly behind the scutum. The prsescutum and post- scutellum are usually mi- nute and crowded down out of sight between the oppos- ing segments. As seen in Fig. 90, the prsescutum of most moths (Telea) is a small rounded piece, bent vertically down so as not to be seen from above. In Polystoechotes and also in Hepialus the prsescutum is large, well-developed, tri- angular, and wedged in between the two halves of the scutum. The postscutellum is still smaller, usually forming a transverse ridge, and is rarely used in taxonomy. The metathorax is usually smaller and shorter than the mesotho- rax, being proportioned to the size of the wings. In certain Neuroptera and in Hepialidae and some tin- eoid moths, where the hind wings are nearly as large as those of the anterior pair, the meta- thorax is more than half or nearly two-thirds as large as the mesothorax. In Hepialidse the pra?scu- tum is large and distinct, while the scutum is di- vided into two widely separated pieces. The postscutellum is nearly or quite obsolete. The pleurum in each of the three thoracic segments is divided into two pieces ; the one in front is called the episternum, since it tr" FIG. 91. — Thorax of the house-fly: j»'n, pronotum prxi1, pnesciitiini ; «•', niesoscutum ; ••«•/', inesoscutelhim jixcf, postscutellum ; a/, insertion of sijuaina. extending to the insertion of the wings, which have been removed •tnn/i/ir, iiu'sophragma ; //. balancer (halter); pt, tegula i>/tii, iiietiiiiotiim ; I'/II'M, ejn'x', c/i/.-,", e|pisternum of pro-, nii'Mi . and meta-thorax ; rji/ti', cpi/i", niesu- and tneta- ' " ' " xf, xf". nicso- and meta-sternuin ; <•.;•'. ex' ; tr'. tr", tr'", trocliaiiters of the three pairs of legs; x/i', x/i", up'", xp"", up'"", first to fifth spir- acles; /(/', ft/", terirites of first and second abdominal THE PATAGIA AND TEGULAE 89 rests upon the sternum ; the other is the epitnernm. To these pieces, with the sternum in part, the legs are articulated (Fig. 89). Between the episterna is situated the breastplate or sternum, which is very large in the more primitive forms, as the Orthoptera, and is small in the Diptera and Hymenoptera. The episterna and epimera are in certain groups, Neuroptera, etc., further subdivided each into two pieces (Fig. 102). The smaller pieces,. hinging upon each other and forming the attachments of the muscles of flight, differ much in shape and size in insects of different orders. The difference in shape and degree of differentiation of these parts of the thorax is mentioned and illustrated under each order, and reference to the figures will obviate pages of tedious description. A glance, however, at the thorax of a moth, fly, or bee, where these numerous pieces are agglutinated into a globular mass, Avill show that the spherical shape of the thorax in these insects is due to the enlargement of one part at the expense of another ; the prothoracic and metathoracic segments being more or less atrophied, while the mesothorax is greatly enlarged to support the powerful muscles of flight, the fore wings being much larger than those appended to the metathorax. In the Diptera, whose hinder pair of wings are reduced to the condition of halteres, the reduction of the metathorax as well as prothorax is especially marked (Fig. 91). The patagia. — On each side of the pro- notum of Lepidoptera are two transversely oval, movable, concavo-convex, erectile plates, called patagia (Fig. 92). On cutting those of a dry Catocala in two, thev will be seen to be J , Fio. 92. — Prothorax of hollow. Cnoloakowsky states that they are ffeometra papiUoruiria : 11, notuni ; ]>, pleura; fit, tilled with blood and trachea! branches; and sternum; j>t, patagia; m, . membrane ; f\ femur ; h, a lie went so far as to regard them as rum- i»«>ok bent 'backwards and . , beneath, and connecting the mentary prothoracic wings, in which view he pro- with tin- mesothorax. - , . After Cholodkovsky. was corrected by Haase,- who compares them with the tegulae, regarding them also as secondary or accessory structures. The tegulae. — On the mesothorax are the tegiduz of Kirby (ptery- fforJes of Latreille, parapt^ra of McLeay, hypopt&re or stpKiirmle), which cover the base of the fore wings, and are especially developed in the Lepidoptera (Fig. 90, A, f) and in certain Hymenoptera (Fig. 95, c). 1 Cholodkowsky, Zool. Anz., ix, p. 615 ; x, p. 102. 2 Zool. Anz., ix, p. 711. 90 TEXT-BOOK OF ENTOMOLOGY The external opening of the spiracles just under the fore wings, is situated in a little plate called by Audouiu the peritrzme. In the higher or aculeate Hymenoptera, besides the three segments normally composing the thorax, the basal abdominal segment is during the change from the larva to the pupa transferred to this region, making four segments. This first abdominal is called " the median segment" (Figs. 93-95). In such a case the term alitrunk D —p FIG. 93. — Transformation of the bumble bee, Bombus. showing the transfer of the 1st abdominal larval segment (<•) to the thorax, forming the propodeum of the pupa ( />> and imago ; 11, spiracle of the propodeum. A, larva; ( y •• i s tern urn of metathorax" (Brauer)=metapleura of Oj-tni Sacken); 6, and also //, halter; xtl, iiH'Snthoracic sti^nui : xt2, metathoracic stigma; */3, first abdominal stigma; y, dorsopleural ; 5, sternopleural ; e, mesopleural sutures; h, 1st, i, 2d, abdominal segment; *t. pra-ster- num, divided into 4 pit-ci". ; xt, pro-, «/', meso-, at", metasternum ; ex, coxa; not, notum. processes, or apodemes, which pass inward and also form attach- ments for the muscles. Those passing up from the sternum form the entothorax of Audouin, and the process of each thoracic segment is called respectively the aiit- Kterrnmi; 'i.f, (•pi>l»'riiiiin ; 'Ui, cpinu'rum; 2.«, antci'iirca or entothorax. THE APODEMES 93 The medifurca is a pair of flat processes which diverge and bridge the commissure, while the postfurca is situated under the commissure. In beetles (Dyticus) Newport states that it is ex- Fi<*. 98. — Mesii- (fj'2i and metathoracic ganglia. ( (?i\ with the apodemes of Gryllo- talpa. — After Graber. Fir;. 00. — Parts of the mesothorax of Dyticus : .^.inesosternuin ; 3.«, pnescutum ; o.//, scutum; 3.C1, scutellum ; 3.rf, postscutellum ; H.c, paran- teron ; S.(/, inesosternum ; 3./, epistermmi ; 3.A, epiiiicriun ; 3..v, incrtifurca or entothorax. panded into two broad plates, to which the muscles of the pos- terior legs are attached. Graber also notices in the mole cricket between the apodemes of the meso- and metathorax, a flattened spine (Fig. 98, do) with two perforations through which pass the commissures con- necting the ganglia. Besides these processes there are large, thin, longitudinal par- titions passing down from the tergum (or dorsum), called phragmas; they are most developed in those insects which fly best, i.e. in Coleoptera (Figs. 97-101), Lepidoptera, Diptera, and Hymenoptpra, none being sternum ; 4.ij, metasternum ; 4. li, epimenim , 4.0, developed in the prothorax. postfurca.— This and Figs. y7 and '.»'J from Audouin, after Newport. (The term phragma has also been applied to a partition formed by the inflexed hinder edge of this segment, and is present only in those insects in which the prothorax is movable. — Century Dictionary.) All these in- pIO ion. —Parts of the metathorax of Dyticus: A, metustfriiuin ; 4.eutelluiii : 4.<-, |iiini|iti-nui ; 4./, epi 94 TEXT-BOOK OF ENTOMOLOGY growths may be in general termed apodemes. There are similar structures in Crustacea and also in Limu- lus; but Sharp restricts this term to minute projections in beetles (Goliathus) situ- ated at the sides of the thorax near the wings. (In- secta, p. 103, Fig. 57.) The internal processes arising from the sternal region have been called endosternites. The acetabula. — These are the cavities in which the legs are inserted. They are situated on each side of the posterior part of the ster- num, in each of the thoracic segments. They are, in gen- eral, formed by an approxi- mation of the sternum and epimerum, and sometimes, also, of the episternum, as in Dyticus (Fig. 97, A). This consolidation of parts, says Newport, gives an amazing increase of strength to the segments, and is one of the circumstances which enables the insect to exert an aston- ishing degree of muscular power. Fio. 101. — Internal skeleton of f.it- ea»i/ti cft-ruti. , iiicta^cutiuii ; 4 c, tm-taseutellum ; 4 , tcjrnlii; 4 /, episternuin ; 4 h, opimcruin ; 4 tcriiiiin : 4 X' and /, coxa : 4 ;/(, trochanter; n, femur; o, tibia;;/, tarsus; 7. unguis; 7-11, abdominal segments. — After Newport. etc., Fig. 104) it is usually divided into two pieces, though there are some exceptions. The trochanter is succeeded by the femur, tibia, and tat-situ, the latter consisting of from one to rive segments, the normal number being five. Tuff en West believed that the pulvillus is the homologue of an additional tarsal joint, "a sixth tarsal joint." The last tarsal segment ends in a, pair of freely movable claws (ungues), which are modified sette ; between the claws is a cushion- THE LEGS: THEIR STRUCTURE AND FUNCTIONS 07 JIIESO META. FIG. 103. — Side view of meso- and meta- thorax of Jfantixjiti !>ritnnr 101> See beneath each or nearly each tarsal joint. The triunguline larvse of the Meloidae are so called from apparently having three ungues, but in reality there is only a single claw, with a claw-like bristle on each side. Why do insects have but six legs ? — Embryology shows that the ancestors of insects were polypodous, and the question arises to what cause is due the process of elimination of legs in the ancestors of existing insects, so that at present there are no functional legs on the abdomen, these being invariably restricted (except in caterpillars) to the thorax, and the number "never being more than six. It is evident that the number of six legs was fixed by heredity in the Thysanura, before the appearance of winged insects. We had thought that this restriction of legs to the thorax was in part due to the fact that this is the centre of gravity, and also because abdominal legs are not necessary in locomotion, since the fore legs are used in dragging the insect forwards, while the two hinder pairs support and push the body on. Synchronously with this elimination by disuse of the abdominal legs, the body became shortened, and subdivided into three regions. On the other hand, as in caterpillars, with their long bodies, the abdominal legs of the embryo persist; or if it be granted that the prop-legs are secondary structures, then they were developed in larval life to prop up and move the abdominal region. The constancy of the number of six legs is explained by Dahl as being in rela- tion to their function as climbing organs. One leg, he says, will almost always be perpendicular to the plane when the animal is moving up a vertical surface ; and, on the other hand, we know that three is the smallest number with which stable equilibrium is possible ; an insect must therefore have twice this number, and the great numerical superiority of the class may be associated with this mechanical advantage. (This numerical superiority of insects, however, seems to us to be rather due to the acquisition of wings, as we have already stated on pages 2 and 120. ATROPHY OF LIMBS BY DISUSE 101 Loss of limbs by disuse. --Not only are one or both claws of a single pair, or those of all the feet atrophied by disuse, but this pro- cess of reduction may extend to the entire liinb. In a few insects one of the claws of each foot is atrophied, as in the feet of the Pediculidse, of many Mallophaga, all of the Coccidfe, in Bittacus, Hybusa (Orthoptera), several beetles of the family Pselaphidse, and a weevil (Brachy- bamus). Hoplia, etc., bear but a single claw on the hind feet, while the allied Gynmolonia has only a single claw on all the feet. Cybister has in general a single immovable claw on the hind feet, but Cybister scutellaris has, according to Sharp, on the same feet an outer small and movable claw. In the water bugs, Belostoma, etc., the fore feet end in a single claw, while in others (Corisa) both claws are wanting on the fore feet. Corisa also has no claws on the hind feet ; Notouecta has two claws on the anterior four feet, but none on the hind pair. In Diplonychus, however, there are two small claws present. (Kolbe.) Among the Scarabseidse, the individuals of both sexes of the fossorial genus Ateuchus (A. sacer) and eight other genera, among them Deltochilum gibbosum of the United States, have no tarsi on the anterior feet in either sex. The American genera Phanseus (Fig. Ill), Gromphas, and Streb- lopus have no tarsal joints in the male, but they are present in the female, though much reduced in size, and also wanting, Kolbe states, in many species of Pha- nseus. The peculiar genus Steno- sternus not only lacks the anterior feet, but also those of the second and third pair of legs are each reduced to a vestige in the shape of a simple, spur-like, clawless joint. The lingual joint is want- ing in the weevil Anoplus, and becomes small and not easily seen SI.' vb in four other genera. FIG. 110. — Last tarsal joint of Melolontha vulgttrix, drawn as if transparent to show the inner mechanism : un, claws ; xlr, extensor plate ; *, tendon of the flexor muscle ; rli, elas- tic membrane between the extensor plate and the sliding surface u ; krh, process of the lin- gual joint; fiiip, extensor spine, and th, its two tactile hairs. — After Ockler, from Kolbe. Ryder states that the evidence that the absence of fore tarsi in Ateuchus is due to the inheritance of their loss by mutilation is uncertain. Dr. Horn sug- gests that cases like Ateuchus and Deltochilum, etc., "might be used as an evidence of the persistence of a character gradually acquired through repeated mutilation, that is, a loss of the tarsus by the digging which these insects per- form." On the other hand, the numerous species of Phanseus do quite as much digging, and the anterior tarsi of the male only are wanting. " It is true," he adds, " that many females are seen which have lost their anterior tarsi by digging ; have, in fact, worn them off ; but in recently developed specimens the 102 TEXT-BOOK OF ENTOMOLOGY FIG. 111. — Fore tibia of Ph< tit />• it >t carnifeu', cf, showing no trace of the tarsus. front tarsi are always absent in the males and present in the females. If repeated mutilation has resulted in the entire disappearance of the tarsi in one fossorial insect, it is reasonable to infer that the same results should follow in a related insect in both sexes, if at all, and not in the male only. It is evident that some other cause than inherited mutilation must be sought for to explain the loss of the tarsi in these insects." (Proc. Amer. Phil. Soc., Philadelphia, 1889, pp. 529, 542.) The loss of tarsi may be due to disuse rather than to the inheri- tance of mutilations. Judging by the enlarged fore tibiae, which seem admirably adapted for digging, it would appear as if tarsi, even more or less reduced, would be in the way, and thus would be useless to the beetles in dig- ging. Careful observations on the habits of these beetles might throw light on this point. It may be added that the fore tarsi in the more fossorial Cara- bidse, such as Clivina and Scarites, as well as those of the larva of Cicada and those of the mole crickets (Fig. 112), are more or less reduced ; there is a hypertrophy of the tibiae and their spines. The shape of the tibia in these insects, which are flattened with several broad triangular spines, bears a strong resem- blance to the nails or claws of the fossorial limbs of those mam- mals which dig in hard soil, such as the armadillo, manis, aardvark, and Echidna. The principle of modification by disuse is well illustrated in the following cases. In many butterflies the fore legs are small and shortened, and of little use, and held pressed against the breast. In the Lycse- nidse the fore tarsi are without claws ; in Erycinidae and Liby- theidae the fore legs of the males are shortened, but completely de- veloped in the females, while in the Nymphalidae the fore legs in both sexes are shortened, consist- ing in the males of one or two joints, the claws being absent in the females. Among moths loss of the fore tarsi is less frequent. J. B. Smith * notices the lack of the fore tarsi in the male of a deltoid, Litognatha nubilifasciata (Fig. 113), while the hind feet of i Ent. Amer., v, p. 110, PI. II, Fig. 7. B FIG. 112. — Fore leg of the mole-cricket: ^4, B, inner, aspect ; e, ear-slit. — After MECHANICS OF WALKING 103 Hepialus hectus are shortened. In an aphid (Mastopoda pteridis, CEsl.) all the tarsi are reduced to a single vestigial joint (Fig. 114). Entirely legless adult insects are rare, and the loss is clearly seen to be an adapta- tion due to disuse ; such are the females of the Psychidae, the females of several genera of Coccidse (Mytilaspis, etc.), and the females of the Stylopidae. Apodous larval insects are common, and the loss of legs is plainly seen to be a secondary adaptive feature, since there are annectant forms with one or two pairs of thoracic legs. All dipterous and siphonap- terous larvae, those of all the Hymenoptera except the sawflies, a few lepidopterous larvae, some coleopterous, as those of the Rhyncophora, Buprestidse, Eucnemidse, and other families, and many Cerambycidee are without any legs. In EupsaUs minuta, belonging to the Brenthidae, the thoracic legs are minute. The legs of larvae end in a single claw, upon the tips of which the insect stands in walking. sh- FIG. 1 13. — Leg- of Litognatka : cee, coxa; /, femur; I, tibia; <:j>, its epiphysis, and .sA, its shield-like process. "The tarsus entirely want- ing. — After Smith. c. Locomotion (walking, climbing, and swimming) Mechanics of walking. --To Graber we owe the best exposition of the mechanics of walking in insects. "The first segment of the insect leg," he says, "upon which the weight of the body rests first of all, is the coxa. Its method of articulation is very differ- ent from that of the other joints. The enartlirosis affords the most extensive play, particularly in the Hymenoptera and Diptera." In the former the development of their social conditions is very closely con- nected with the freest possible use of the legs, which serve as hands. In the beetles, however, which are very compactly built, there exists a solid articula- tion whereby the entire hip rests in a tent-like excavation of the thorax, and can only be turned round a single axis, as may be seen in Fig. 115, where c repre- sents the imaginary revolving axis and d the coxa. In the case we are suppos- ing, therefore, only a backward and forward movement of the coxa is possible, the extent of the play of which depends on the size of the coxal pan, as well as certain groin or bar-like structures which limit further rotation. In the very dissimilar arrangement which draws in the fore, middle, and hind legs toward the body it is self-evident that their extent of action is also different. This arrangement seems to be most yielding on the fore legs, where the hips, to con- fine ourselves to the stag-beetles, can be turned backward and forward 60° from 104 TEXT-BOOK OF ENTOMOLOGY the middle or normal position, and therefore describe on the whole a curve of 120°. The angle of turning on the middle leg hardly exceeds a legitimate limit, yet a forward as well as a backward rotation takes place. The former is entirely wanting in the hind hips ; they can only be moved backward. The number and strength of the muscles on which the rotation of the hips depends, correspond with these varying movements of the individual legs. Thus, according to Straus Durckheim, the fore coxa of many beetles pos- sesses five separate muscles and four forward and one backward roll ; the middle coxa a like number of muscles but only two forward rolls, while the hind hips succeed in accomplishing each of the motions named with a single muscle. One can best see how these muscles undertake their work, and above all how they are situated, if he lays bare the FIG. 114. — Leg of an Aphid, with the tarsus (f) much reduced : 1, 2, 3, legs of 1st, 2d, and 3d pairs. prothorax of the stag beetle (Fig. 116). Here may be seen first the thick muscle which turns to the front the rotating axis in its cylindrical pan, and thus helps to extend the leg, while two other tendons, which take the opposite direction, are fitted for reflex movements. FIG. 115 —Mechanics of an insect's leg: d, coxa, — c,, axis of revolution ; a and J>, the coxal museles; e, troehantcr muscle (elevator of the femur); ./', extensor, — ;/, flexor, of the tihia (/>»); //. tibial s|iine; h. flexor.— i, extensor, of the foot: k. extensor,—/, flexor, of the claw; /<«, place nf llexnre of the tibia; y/'.y. le«r after beiiiy turned l.aek by the coxa, — f>lr, by the simul- tani s tlexiire of the tibia The resulting motion of the end of the tibia, through the simul- taneous movement (»o) and revolution (mj), indicates the curve nr. — After (iraher. In Fig. 115 the muscles mentioned above, and their modes of working, may be distinguished by the arrows a and b. In order to simplify matters, we will imagine the second component part MECHANICS OF WALKING 105 of the normal insect leg, i.e. the trochanter (Figs. 116, 117, r), as grown together with the third lever, i.e. the femur, as the movement of both parts mostly takes place uniformly. The pulling of the small trochanter muscle works against the weight of the body when this is carried over on to the trochanter by means of the coxa, as seen at the arrow e in Fig. 115. It may be designated as the femo- ral lever. The plane of direction in which the femur, as seen by the rotation just mentioned, is moved, exactly coincides in insects with that of the tibia and the foot, while all can be simultaneously raised or dropped, or, as the case may be, stretched out or retracted. Therein, therefore, lies an essential difference from the fully developed extremities of verte- brates among which, even on the lever arms which are stationary at the end, an extensive turning is possible. The muscles which move the tibia, and indirectly the femur, also consist of an ex- tensor muscle which is situated in the upper side of the femur (Fig. 116, s, Fig. 115, /), and of a flexor (Fig. 116, b, Fig. 115, 0), which lies under the former. The stilt-like spines on the point (Figs. 115 and 118, Lzn) on which this segment is directly supported are important parts of the tibia. (Graber.) Considering the respective positions of the individual levers of the leg and FIG. 116 —Section of the fore leg of a stag-beetle, showing the muscles: S, ex- tensor, — B, flexor, of the leg ; s, exten- sor, — b, flexor, of the femur ; o. femur ; v, tibia ; ./', tarsus ; k, claw ; 109, s, ex- tensor,— b, flexor, of the femoro-tibial joint, both enlarged. — After Graber. FIG. the nature of the materials of which they are made, the legs of insects may be likened, as Graber states, to elastic bows, which,when pressed down together from above, their own indwelling elasticity is able to raise again and thus keep the body upright. This is very plainly shown in certain stilt-legged bark-beetles, in which, as in a rubber dull, as soon as the body is pressed down on the ground, the organs of motion extend again without the intervention of muscles ; indeed this experiment succeeds even with dead, but not yet wholly stiff, insects. Graber then turns to the analysis of the 117. — Left fore leg of a cid beetle: h, coxa; r, trochanter; o, femur; u, tibia; /, tarsus ;£,claw. — After Graber. movements of illSCCt legs when ill motion, 106 TEXT-BOOK OF ENTOMOLOGY and the mode of walking of these insects in general. This subject had been but slightly investigated until Graber made a series of observations and experiments, of which we can give only the most important results. The locomotion of insects is an extremely complicated subject. Let us consider, Graber says, first, a running or carabid beetle, when walk- ing merely with the fore and hind legs. The former will be bent forward and the latter backward. "Let us begin with the left fore leg (Fig. 118, LI}. Let the same be ex- tended and fixed on the ground by means of its sharp claws and its pointed heel. Now what happens when the tibial flexors draw together ? As the foot, and therefore the tibia also, have a firm position, then the contraction of the muscles named must cause the femur to approach the tibia, whereby the whole body is drawn along with it. This individual act of motion may be well studied in grasshoppers when they are climbing on a twig by stretching out their long fore leg directly forward, and then drawing up the body through the shortening of the tibial flexors until the middle leg also reaches the branch. " But while the fore legs advance the body by drawing the free lever to the fixed leg-segment, the hind legs do this in exactly the opposite way. The hind leg, namely, seeks to stretch out the tibia, and thus to increase the angle of the knee (-R3), thereby giving a push on the ground, by means of which the body is shoved forward a bit. "Though it might be supposed that the feet would remain stationary during the extension or retraction of the limbs, this never occurs in actual walking. Not merely the upper, but also the lower, thigh is either drawn in or stretched out, as the case may be. The latter then describes a straight line with its point during this scraping or scratching mot inn (Fig. 115, no), which is obviously the chord to that quadrant which would be drawn by the tibia or foot in a yielding medium, as water, for instance. But even this motion results extremely rarely, and never in actual walking. If we fix our eye anew upon the fore leg at the very moment when it is again retracted, after the resultant ' fixing,' we shall then observe that the hip also is simultaneously .turned backward in a definite angle. The tibia would describe the arc nq (Fig. 115) by means of the lat- ter alone. "This plane, in conjunction with the rectilinear 'movement' (no) obtained by the retraction of the tibia, produces a path («>•), and this is what is actually described by a painted foot upon a properly prepared surface, as a sheet of paper ; l supposing, however, that the body in the meantime is not moved for- ward by other forces. In the last case, and this indeed always takes place in running, the trunk is moved a bit forward, together with the leg which is just describing its curve with a rapidity corresponding to the momentum obtained; the result of this is that the curve of the foot from its beginning (H) to its end (a) bends round close to itself, just as a man who, when on board a ship in nil 'i ion, walks across it diagonally, and yet on the whole moves forward, be- cause his line of march, uniting with that of the ship, results in a change of position in space. 1 In his account of his studies on the locomotion of insects, De Moor states that he obtained the track of each of the feet in different colors by coating them with differ- ent pigments ; the insect, as it moved, left its track on a strip of paper. (Archives de Biologie, Liege, 18'JO.) MECHANICS OF WALKING 107 "The case is the same in the middle and hind legs, which must make a double course also, yet in such a way that the straight line is drawn, not during the retraction, but during the extension ; during which, however, quite as in the fore leg, the members mentioned (Us) gradually approach the body. " When the legs have reached the maximum of their retraction, or of their extension, as the case may be, and therefore the end of their active course for that time, then begins the opposite or backward movement ; that is, the fore legs are again extended, while their levers draw the remaining legs together again. R, FIG. 118. —A Carabus beetle in the act of walking or running : three leg's (Z,, 7?2, L3} are directed forward, while the others (7?t, Z2, R^, which are directed backward toward the tail, have ended their activity ; nfi, <•, the active curve passing inward, — be and t/e, the passive going outward. (', two curves described by the left hind legs ; in this case, the curves are not inwards or backwards, but partly directly inward (/>), and in part obliquely forwards (a). and a stag-beetle (Fig. 121, c). The actual faint line in this case does not run from the front toward the back, as would correspond to the active leg-motion, but either directly inward (Fig. 121, ch), or even somewhat to the front. In the May-beetles, and even more in the running garden-beetle, the curves of the hind legs present themselves as screw-like lines (Fig. 122, /3), while the scrawl- ing of the remaining members (/t, 72) is much simpler. " Inasmuch as we now have a cursory knowledge of the movements made by each individual leg for itself, — movements, however, which plainly occur very differently according to the structure of these appendages, — the question now is of the combined play, the total effect of all the legs taken together, and there- fore of the walk and measure of the united work of the foot. "In opposition to the caterpillars and many other crawling animals which extend their legs in pairs and really swing them by the worm-like mode of con- traction of the- dermomuscular tube, the legs of fully grown insects are moved in the contrary direction and in no sense in pairs, but alternately — or, more strictly speaking, in a diagonal direction. MECHANICS OF WALKING 109 "For an examination of the gait of insects, we choose, for obvious reasons, those which have very long legs and which at the same time are slow walkers. " Insects'may be called ' double-three-footed,' from the manner in which they alternately place their legs. There are always three legs set in motion at the same time, or nearly so, while in the meantime the remaining legs support the " ndy, after which they change places. "To be more exact, it is usually thus: At first (Fig. 118) the left fore leg (ii) steps out, then follows the right middle leg (.#2), and the left hind leg (£3). Then while the left fore leg L ^ begins . to retract and thus make the backward move- ment, the right fore leg is extended, whereupon the left middle leg and the right hind leg are raised in the same order as the first three feet." 7 00 0< if Sh \° o/. \ 0| "O FIG. FIG. 123. FIG. 124. i), middle (72), and hind, leg (fa) of a Carabus. Natural FIG. 122. — The same by the left fore size. FIG. 123. — Tracks of a Blapx ninrfixaga marked by the differently painted tibial points: O, tracks of fore, — O, middle, — /, hind leg. Natural si/e. FIG. 124. — Tracks of Xecrophm •>/.•< rrxjii/io. Natural size. Graber1 painted the feet of beetles and let them run over paper, and goes on to say : " Let us first pursue the tracks of the Blaps, for example (Fig. 123). Let the insect begin its motion. The left fore leg stands at «, the right middle leg at 13, and the left hind leg at c. The corresponding number of the other set of three feet at a, b, 7. At the first step the three feet first mentioned advance to a'Q'c', the second set on the other hand to a'b'y'- Thereby the tracks made by the successive steps fall quite, or almost quite, on each other, as appear also in the tracks of a burying beetle (Fig. 124). "As the fore legs are directed forward and the hind legs backward, while the middle legs are placed obliquely, the reason of the more marked impressions of the latter is evident. "The highest testimony to the precise exactitude and accuracy of the walking mechanism of insects is furnished by the fact that in most insects, and par- ticularly in those most fleet of foot, which, whether they are running a\v;iy or chasing their prey, must be able to rely entirely upon their means of loco- motion ; — the fact, we say, that whether they desire to move slowly or more 1 Carlet and also De Moor (1890) confirm Graber's statement that in beetles the first and last appendages on the same side are in contact with the ground, while the middle one is raised. On the other side of the body the middle appendage is on the ground and the first and last one raised. 110 TEXT-BOOK OF ENTOMOLOGY quickly, the distances of the steps, measured by the length as well as by the cross-direction, hardly differ a hair's breadth from one another, and this is also the case when the tarsi are cut off and the insects are obliged to run on the points of their heels (tibiae). " Thence, inasmuch as the trunk of insects is carried by two legs and by one on each side alternately, it may surely be concluded a priori that when walking it is inclined now to the right and now to the left, and that the track, too, which is left behind by a precise point of the leg, can in no wise be a straight line ; and in reality this is not the case. "A plainly marked regular curve, which approaches a sinuous line, as seen in Fig. 125, is often obtained by painting many insects, for example Trichodes, Meloe, etc., which, when running, either bring the end of their hind body near to the ground or into contact with it. "The locomotive machine of insects may be called, to a certain extent, a double set of three feet each, as most insects, and particularly those provided i with a broad trunk, are able to balance themselves with *\ one of these two sets of feet, and indeed when walking, I-A«°, °. • as well as when standing still, can move about even better with one set of these feet than with four legs. In the latter *J • 0 • 0 • 0 .0 \ o • \ '• o , \ o» \ V \ o V 0/E1 \p * i FIG. 125. \ V V FIG. 126. FIG. 127. FIG. 125. —Tracks of Trichodes; the middle sinuous line is made by the tip of the abdomen. Natural size. FIG. 12(5. — Tracks of another insect which, in running-, can only use three legs (t\, 74, r3) which become indicated differently from normal conditions. Natural size. FIG. 12T. — The same of an insect crossing over a surface inclined 30° from the horizon, whereby the placing- of the feet becomes changed. Natural size. — This and Figs. 120-126 after Graber. case, that is, if one cuts off a pair of legs from an insect, the trunk can balance itself only with extreme difficulty, and there is therefore little prospect that insects will ever become four-footed. " But if one compels insects to run on three legs, he will thus make the inter- esting discovery that to make up the deficiency they place the remaining feet and bring them to the ground somewhat differently than when the second set of feet is active. Figs. 124 and 120 may be compared for this purpose. The former shows the footprints of a burying beetle running with all six legs, the latter the track of the same insect, which, however, has at its disposal only the right fore leg, the left middle leg, and the right hind leg. One may plainly see here that the track of the hind leg on the right side (r8) approaches the track of the middle leg on (lie left side, and then further, that the right fore leg (r\) steps out more to the right to make up for the deficiency of the middle leg. HOW INSECTS WALK ON SMOOTH SURFACES 111 " A similar adaptation of the position of the legs, which is entirely dependent on the choice of the insect, may also be observed there, if one compels insects which are not provided with corresponding adhesive lobes to run away over crooked surfaces. Fig. 123 shows the footprints of a Blaps when running upon a horizontal plane. Fig. 127, on the contrary, shows the tracks of the legs when going diagonally over a gradually inclined surface. Here, also, the insect holds on with his fore and middle legs (»*i, r2) stretched upward, whereby also the impressions on both sides come to lie farther apart than in the normal mode of walking. " It will not surprise the reader who is familiar with the gait of crabs, to hear that many insects also understand the laudable art of going backward, wherein the hind legs simply change places with the fore legs. " The jumping motion of insects may be best studied in grasshoppers. When these insects are preparing for a jump, they stretch out the upper thigh hori- zontally, clap the tibiae together, and also retract the foot-segment. After a slight pause for rest, during which they are getting ready for the jump, they then jerk the tibiae suddenly backward and against the ground with all their strength by means of the extensor muscles." The correctness of Graber's views has been confirmed by Marey by instantaneous photographs (Figs. 128, 129). Locomotion on smooth surfaces. — How flies and other insects are able to walk up, or run with the body inverted, on hard surfaces has been lately discovered by Dewitz, Dahl, and others. All authors are agreed that this power is due to the presence of the specialized empodium of each tarsus. Dewitz confirmed the opinion of Blackwell, that a glutinous liquid is exuded from the apices of the tenent hairs which fringe the em- podium. By fastening insects feet uppermost on the under side of a covering glass which projects from a glass slide, the hairs which clothe the empodia of the foot of a fly (Musca erythrocephala) may be seen to be tipped with drops of transparent liquid. On the leg being drawn back from the glass, a transparent thread is drawn out, and drops are found to be left on the glass. In cases where these hairs are wanting, as in the Hemiptera, the adhesive fluid exudes directly from pores in the foot. In the beetles (Telephorus Caspar) and other insects the tenent hairs on the foot end in sharp points, below which are placed the openings of the canals. The glands, Dewitz states, are chiefly flask-shaped and unicellular, situated in the hypodermis of the chitinous coat ; each gland opening into one of the hairs (Fig. 108) ; they are each invested by a structureless tunica propria, and contain granular protoplasm, a nucleus placed at the inner side, and a vesicle, prolonged into a tube which, traversing the neck of the gland, is attached to the root of the hair ; the vesicle receiving the secretion. Each gland is connected with a fine nerve-twig, and secretion is probably voluntary. Among the tenent 112 TEXT-BOOK OF ENTOMOLOGY hairs of the empodium are others which must be supplied with a nerve, forming tactile hairs, as they each proceed from a unicellular •a a S •a I c3 ganglion (Fig. 108, «"). The secretion is forced out of the gland by the contraction of the protoplasm, Dewitz having seen the secretion driven out from the internal vesicle into its neck. HOW INSECTS WALK ON SMOOTH SURFACES ll;j D In the spherical last tarsal joint of Orthoptera (Fig. 109), which is without these tenent hairs, nearly all the cells of the hypodermis are converted into uni- cellular glands, each of which sends out a long, fine, chitinous tubule, which is connected with its fellows by jj ^ very fine hairs and is continuous with the chitinous coat of the foot and opens through it. The sole of the foot is elastic and adapts itself to minute inequalities of surfaces, while the anterior of each tarsal joint is almost entirely occupied by an enlargement of the trachea,* which acts on the elastic sole like an air chamber, rendering it tense and at the same time pliant. Dewilz adds that the apparatus situated on the front legs of the male of Stenobothrus sibiricus (Fig. 131) must have the function of causing the legs to adhere closely to the female by the excretion of an adhesive material. The hairs of the anterior tarsi of male Carabi also appear to possess the power of adhe- sion. In the house-fly the empodia seem to be only called into action when the insect has to walk on vertical smooth surfaces, as at other times they hang loosely down. Burmeister observed the use of a glutinous secretion for walking in dipterous larvee, and Dewitz found that the larva of a Musca used for this purpose a liquid ejected from the mouth. The larva? of another fly (Leiifopis puncticornis) perform their loop-like walk by emitting a fluid from both mouth and anus. A Cecidomyia larva is able to leap by fixing its anterior end by means of an adhesive fluid. The larva of the leaf-beetle, Galeruca, moves by drawing up its hinder end, fixing it thus, and carrying the anterior part of the body forward with its feet until fully extended, when it breaks the glutinous adhesion. The abdominal legs of some saw-fly larvae have the same power. Dahl could not detect in the foot of the hornet (ye spa crabro) any space which could be considered as a vacuum. Simmermacher states that in most cases of climbing beetles the tubular tenent hairs pour out a secretion (Figs. 1,33, 134), "aud it is probable that we have here to do with the phenomena not of actual attachment by, as it were, gluing, but of adhesion ; the orifice of the tubes is divided obliquely, and the tubes are, at this point, extremely delicate and flexible, so as to adhere by their lower sur- FIG. 130. —A, end of an adhesive hair of a weevil (Kii]iolus) : i", canal: /"', its external opening1 at the end of the hair. £, end of a similar hair of Telephorus with drops of the secretion. — After l)e\vitx. ar P Fro. 131. — Slenobotlirux ftibiricits pair- ing : .4. the J1 , fore tarsus (/) greatly enlarged ; at', arolia ; ]>, pulvillus. — After Pagenstecher. 114 TEXT-BOOK OF ENTOMOLOGY face; in this adhesion they are aided by the secreted fluid." In the case of the Diptera he does not accept the theory by which the movement of the fly along smooth surfaces is ascribed to an alternate fixation and separation, but believes in a process of adhesion, aided by a secretion, as in many Coleoptera. (In the Cerambycidee there is no secretion, and the tubules are merely sucking organs, like those observed in the male Silphidse.) " The attaching lobes, closely beset with chitinous hairs, are enabled, in consequence of the pressure of the foot, to completely lie along any smooth surface ; this expels the air beneath the lobes, which are then acted on by the pressure of the outer air." (Journ. Roy. Micr. Soc., 1884, p. 736.) Another writer (Rombouts) thinks this power is due to capil- lary adhesion. The action of the pul- villus and claws when at rest or in use by the honey- bee is well shown by Chesh- ire (Fig. 135, B). In as- cending a rough surface, "the points of the claws catch (as at B) and the pulvillus is saved from any contact, but if the surface be smooth, so that the claws get no grip, they slide back and are drawn FIG. 132. — Fore leg of $ Dyticus, under side, with sucker, formed of 3 enlarged tarsal joints : with a small beneath the foot (as at A). eupule highly magnified, x 120. — After Miall. which change of position applies the pulvillus, so that it immediately clings. It is the character of the surface, then, and not the will of the bee, that determines whether claw or pulvillus shall be used in sustaining it. But another contrivance, equally beautiful, remains to be noticed. The pulvillus is carried folded in the middle (as at C, Fig. 105), but opens out when applied to a surface ; for it has at its upper part an elastic and curved rod (cr, Figs. 105 and 135), which straightens STRUCTURE OF THE FEET 115 as the pulvillus is pressed down ; C and D, Fig. 135, making this clear. The flattened-out pulvillus thus holds strongly while pulled, by the weight of the bee, along the surface, to which it adheres, but 0 FIG. 138. — Cross-section through a tarsal joint of foreleg of Dyticus. J, showing the stalked chitinous suckers (K), with a marginal bristle on each side: t, trachea; a, an isolated tubule or sucker of Loricera, — b, of Chlaenius, — a, of Gicindela; d, two views of one of Jfeorophorus germanicus, J1. comes up at once if lifted and rolled off from its opposite sides, just as we should pull a wet postage stamp from an envelope. The bee, then, is held securely till it attempts to lift the leg, when FIG. 134. — Section through the tarsus of a Staphylinid beetle; the glandular or tenent hairs arising from chitinous processes. A, section through the tarsal joint of the pine weevil, Ilylnl'iitx abietis, showing the crowded, bulbous, glandular, or tenent hairs arising from unicellular glands. — This and Fig. 133 after Siinmermacher. it is freed at once ; and, by this exquisite yet simple plan, it can fix and release each foot at least twenty times per second." (Bees and Bee-keeping, p. 127.) Ockler divides the normal two-clawed foot into three subtypes : 110 TEXT-BOOK OF ENTOMOLOGY (1) with an unpaired median empodium ; (2) with two outer lateral adhesive lobes ; (3) with two adhesive lobes below the claws ; the latter is the chief type and forms either a climbing or a clasping foot, The amount of movement possessed by the claws is limited, and what there is, is effected by means of an elastic membrane and 'xn FIG. 135. — Honey-bee's foot in the act of climbing, showing the automatic action of the pulvillus, x 3d : .-1, position of foot in climbing- on a slippery surface, or glass ; pr, pulvillus ; fh, tactile hairs ; mi. iniguis ; t, last tarsal joint. £, position of foot in climbing- rough surface. C, section of pul- villus just touching flat surface; cr, curved rod. D, the same applied to the surface. — After Cheshire. the extensor plate (Fig. 110). The " extensor sole " which is always present in insects with an unpaired median fixing or adhesive organ (empodium) is to be regarded as a modification of the extensor seta. The extensor plate is peculiar to an insect's foot. Ockler states that the so-called " pressure plate " of Dahl is only a movably articulated, skeletal, supporting plate for the median fixing lobule. Climbing. - - In certain respects the power of climbing supplies the want of wings, and even exists often in house-flies among Avhich there is shown a many-sided motion that is quite unheard of in other groups of insects. The best climbers are obviously those insects which live on trees and bushes, as, for example, longicorn beetles and grasshoppers. These may be accurately called the monkeys of the insect kind, even if their movements take place less gracefully, and indeed rather stiffly and woodenly. We already know what are the proper climbing organs; that is, the sharp easily movable claws on the foot. With the help of these claws certain insects, May-beetles for example, can hang upon one another like a chain; indeed, bees and ants in this manner bind themselves together into living garlands and bridges. There are still added to the chitinous hooks flaps and balls of a sticky nature, by help of which likewise the insects glue iht'inst'lves together. To facilitate the spanning of still thicker 1\vigs, the climbing foot of insects has a greater movability even than when it only serves as a sole. (Graber.) The mode of swimming of insects. - - To study the swimming move- ments of insects, let us examine a Dyticus. It will appear, as Graber states, to be wonderfully adapted to its element. HOW INSECTS SWIM 117 "The body resembles a boat. There is nowhere a projecting point or a sharp corner which would offer unnecessary resistance to motion ; bulging out in the middle and pointed at the ends, it cuts through the resistance of the water like a wedge. The movable parts, the oars, seem to be as well fitted for their purpose as the burden to be moved by them. That the hind legs must bear the brunt of this follows from their position exactly in the middle of the body, where it is widest. In other insects also these legs are used for the same purpose as soon as the insects are put in the water. But the swimming legs of water- beetles are oars of quite peculiar construction. They are not turned about in the coxce, as an- vtlii'r leys, but at the foot-joint. The coxa, namely, has grown entirely together with the thoracic partition. The muscles we have mentioned, exceeding in strength all the soft parts taken together, take hold directly of the large wing-shaped tendons of the upper thigh, and extend and retract the leg in one of the planes lying close to the abdominal partition. The foot forms the oar, however. It is very much lengthened and still more widened, and can be turned and bent in by separate muscles in such a way that in the passive movement, that is, the retraction, the narrow edge is turned to the fore, and therefore to the medium to be dislodged ; however, as soon as the active push is to be performed and the leg is extended with greater force, it cuts down through the water with its whole width. These effective oar-blades are still considerably enlarged by the hairs arising on the side of the foot, which spread out at the decisive moment. "Every one knows that the oar-blades of swimming beetles always go up and down simultaneously and in regular time. On the other hand, as soon as one puts a Dyticus on the dry land, i.e. on an unyielding medium, it uses its hind legs entirely after the manner of other land insects ; that is, they are drawn in and extended again alternately, as takes place clearly enough from the foot- steps in Fig. 119, A. We learn from this that water insects have not yet, from want of practice, forgotten the mode of walking of land insects. " The forcing up of the water as a propelling power is added to the repulsion produced by the strong strokes of the oars. If the beetle stood up horizontally in the water, he would be lifted up. " As the trunk, however, assumes an oblique position when the insect wishes to swim, one can then imagine the driving up of the water as being divided into two forces, one of which drives the body forward in a horizontal direction, while the other, that is, the vertical component, is supplied by the moving of the oars. The swimming insect is thus, as it were, a snake flying in the water. "The long streamer-like hind legs of many water-bugs, for example Noto- necta, approach more nearly our artificial oars. These legs are turned out from the bottom. " There is no doubt but that the legs of insects, as regards the many-sidedness and exactitude of their locomotive actions, place the similar contrivances of other animals far in the shade. We shall be forced to admire these ingenious levers still more, however, when we take into consideration their energy and strength. That the force with which the locomotive muscles of insects is drawn together is enormous compared with that of vertebrates, we may learn if we try to subdue the rhythmical movements of the thorax of a large butterfly by the pressure of our finger or to open against the insect's will the closed jumping leg of a grasshopper, or the fossorial shovel of a mole-cricket." 118 TEXT-BOOK OF ENTOMOLOGY LITERATUR'E ON LEGS AND FEET MacLeay, W. S. On the structure of the tarsus in the tetramerous Coleoptera of the French entomologists. (Trans. Linn. Soc. London, xv, 1825, pp. 63-73.) Speyer, 0. Untersuchung der Beine der Schmetterlinge. (Isis, 1843, pp. 161- 207, 243-264.) Pokorsky Joravko, A. von. Quelques remarques sur le dernier article du tarse des Hyme'nopteres. (Bull. Soc. imp. Natur. Moscou, 1844, xvii, pp. 149-159. Kef. in Isis, 1848, v, p. 347.) Rossmassler, E. A. Das Bein der Insekten. (Aus der Heimath, I860, 3 kap., pp. 327-334, Fig.) West, Tuffen. The foot of the fly ; its structure and action ; elucidated by com- parison with the feet of other insects, etc. Part I. (Trans. Linn. Soc. London, xxiii, 1861, pp. 393-421, 1 PI.) Sundevail, C. On insektenas extreiniteter saint deras hufoud och munddelar. (Kongl. Vetenskaps Akad. Handlingar. iii, Nr. 9, 1861.) Lindemann, C. Notizen zur Lehre vom ausseren Skelete der Insekten (Gelenke nnd Muskeln der Fiisse). 1 Taf. (Bull. Soc. imp. d. Natur. Moscou, xxxvii, 1864, pp. 426-432.) Liebe, 0. Die Gelenke der Insekten. Chemnitz, 1873. 4°. 1 Taf. Canestrini, J. Ueber ein sonderbares Organ der Hymenopteren. (Zool. Anzeiger, 1880, pp. 421, 422.) Dahl, F. Beitrage zur Kenntnis des Banes und der Funktionen der Insekten- beine. (Archiv f. Naturgesch. 1 Jahrg., 1884, pp. 146-1 93, 3 Taf. Sep., 48 pp. Vorlauf. Mitteil. in Zool. Anz., 1884, pp. 38-41.) Langer, K. Ueber den Gelenkbau bei den Arthrozoen. Vierter Beitrag zur vergleichenden Anatomic und Mechanik der Gelenke. (Denkschriften der Akad. d. Wissensch. Wien, xviii, Bd. Physikal.-mathem. Classe, pp. 99- 140. 3 Taf.) Graber, Vitus. Ueber die Mechanik des Insektenkorpers. (Biolog. Central bl., iv, 1884, pp. 560-570.) Die ausseren mechanischen Werkzeuge der Tiere. ii Teil. Wirbellose Tiere, 1886, pp. 175-182, 208-210. Dewitz, H. Ueber die Fortbewegung der Tiere an senkrechten glatten Flachen vermittelst eines Sekretes. 3 Taf. (Pfluger's Archiv f. d. ges. Physi- ologie, xxxiii, 18S4, pp. 440-481.) Ockler, A. Das Krallengiied am Insektenfuss. (Archiv f. Naturgesch., 1890, pp. 221-262, 2 Taf.) LITERATURE OF LOCOMOTION (WALKING, ETC.) Carlet, G. Sur le mode de locomotion des chenilles. (Compt. rend. Acad. Paris, 1888, cvii, pp. 131-134. Naturwiss. Kundschau, iii Jahrg., 1888, No. 42, p. 543.) De la rnarche d'un insecte rendu tetrapode par la suppression d'une paire de pattcs. (Ibid., pp. 565, 566.) Sur la locomotion des insectes et des arachnidcs. (Ibid., 1879, T. 89, pp. 112), 1125.) — Ueber den Gang eines vierfiissig gemaclit.cn Insckts. (Naturwiss. Rund- schau, viii Jahrg., 1888, pp. 666-667 ; Compt. rend. 1888, cvii.) LITERATURE OF LOCOMOTION 119 Demoor, J. Recherches sur la marche des insectes et des arachnides. Etude experimentale d'Anatomie et de Physiologie compare'es. (Archiv de Bi- ologie, Liege, 1880, 42 pp. 3 Pis.) Ueber das Gehen der Arthropoden mit Beriicksichtigung der Schwankungen des Korpers. (Compt. rend. Acad. d. Sc. Paris, 1890, cxi, pp. 830-840.) Osten-Sacken, C. R. von. Ueber das Betragen des kalifornischen fliigellosen Bittacus (apterus McLachl.). (Wiener Ent. Zeit., 1882, pp. 123.) Dixon, H. H. Preliminary note on the walking of some of the Arthropoda. (Proc. R. Dublin Soc. vii, pp. 574-578, 1802. Also Nature, 1897.) Also the works of Graber, Marey, Cheshire, etc. LITERATURE OP WALKING ON SMOOTH SURFACES Blackwell, J. Remarks on the pulvilli of insects. (Trans. Linn. Soc. London, xvi, 1831, pp. 487-492, 767-770.) Lowne, B. T. On the so-called suckers of Dytiscus and the pulvilli of insects. (Trans. Roy. Micr. Soc., pp. 267-271, 1871, 1 PI.) West, Tuffen. On certain appendages to the feet of insects subservient to hold- ing or climbing. (Journ. of the Proceed. Linn. Soc. London, Zoology, vi, 1862, pp. 2(5-88.) Dewitz, H. Ut-ber die Fortbewegung der Tiere an senkrechten, glatten Flachen vermittelst eines Sekrets. (Pfliiger's Archiv f. d. ges. Physiologie, xxxiii, 1884, pp. 440-481. 3 Taf. Also Zool. Anzeiger, 1884, pp. 400-405.) Wie ist es den Stubenfliegen und anderen Insekten moglich, an senkrechten Glaswanden emporzulaufen. (Sitzungsb. Ges. naturf. Freunde zu Berlin, 1882, pp. 5-7.) Weitere Mitteilungen iiber den Kletterapparat der Insekten (Ibid., 1882, pp. 109-113). Die Befestigung durch einen klebenden schleim beim springen gegen senk- rechte Flachen. (Zool. Anzeiger, 1883, pp. 273, 274.) Ueber die Wirkung der Haftlappchen toter Fliegen. (Ent. Xachr., x Jahrg., 1884, pp. 286, 287.) Weitere Mitteilungen iiber das Klettern der Insekten an glatten senkrech- ten Flachen. (Zoolog. Anzeiger, 1885. viii Jahrg., pp. 157-159.) — Richtigstellung der behauptungen des Herrn F. Dahl. (Archiv f. niikro- skop. Anat., 1885, xxvi, pp. 125-128.) Rombouts, J. E Ueber die Fortbewegung der Fliegen an glatten Flachen. (Zool. Anzeiger, 1884, pp. 619-623.) De la facult^ qu'ont les mouches de se mouvoir sur le verre et sur les autres corps polis. (Archiv Museum Teyler (2), 4 Part, pp. 16. Fig.) Simmermacher, G. Untersuchungen iiber Haftapparate an Tarsalgliedern von Insekten. (Zeitschr. f. wissensch. Zool. xl, 188-4, pp. 481-556. 3 Taf., 2 Figs. Also Zoolog. Anzeiger, vii Jahrg., 18S4, pp. 225-228.) Antwnrt an Herrn Dr. II. Dewitz. (Ibid., pp. 513-517.) Dahl, F. Die Fussdriisen der Insekten. (Archiv f. mikroskop. Anat., 1885, xxv, pp. 236-263. 2 Taf. See also p. 118.) Emery, C. Fortbewegung von Tieren an senkrechten und iiberhangenden glatten Flachen. (Biolog. Centralbl., 1884, 4 Bd., pp. 438-443.) Leon, N. Disposition anntnniiqut' des orgaiies de surrion chez les Ilydrocores et les Geocores. (Bull. Soc. des Medec. et Natur. de Jassy., 1888.) 120 TEXT-BOOK OF ENTOMOLOGY d. The wings and their structure The insects differ from all other animals except birds in possessing wings, and as we at the outset have claimed, it is evidently owing to them that insects are numerically so superior to any other class of animals, since their power of flight enables them to live in the air out of reach of many of their enemies, the greatest destruction to insect life occurring in the wingless larval and pupal stages. The presence of wings has exerted a profound influence on the shape and structure of the body, and it is apparently due to their existence that the body is so distinctly triregional, since this feature is least marked in the synapterous insects. The wings are thin, broad leaf-like folds of the integument, attached to the thorax and moved by powerful muscles which occupy the greater part of the thoracic cavity. The two pairs of wings are outgrowths of the middle and hinder part of the thorax, the anterior pair being attached to the mesothoracic and the hinder pair to the metathoracic segment. The larger pair is developed from the middle segment of the thorax. The differentiation of the tergites into scutum, scutellum, etc., is the result of the appearance of wings, because these sclerites are more or less reduced or effaced in Avingless insects, such as apterous Orthoptera and moths, ants, etc. The size of the hinder thoracic segments is closely related to that of the wings they bear. In those Orthoptera which have hind wings larger than those of the fore pair, the metathorax is larger than the mesothorax. In such Neuroptera as have the hind wings nearly or quite as large as the anterior pair, or in the Trichoptera and in the Hepialid;e, the metathorax is nearly as large as the mesothorax, while in Coleoptera the metathorax is as large and often much larger. In the Ephemeridse, Diptera, and Hymenoptera, which have either only rudimentary (halteres) or small hind wings, the metathorax is correspondingly reduced in size. The wings morphologically, as their development shows, are simple sac-like outgrowths of the integument, i.e. of the free hinder edge of the tergal plates, their place of origin being apparently above the upper edge, of the epimera or pleural sclerites. Calvert1 however, regards the upper l;miin;i of the wing as tergal, and the lower, pleural. The wings in most insects are attached to the thorax by a mem- brane containing several little plates of chitin called by Audouin articulatory epidemes. 1 Trans. Amer. Eat. Soc. xx, p. 168. STRUCTURE OF THE WING-VE1XS 121 The wings, then, are simple, very thin chitinous lamellate expan- sions of the integument, which are supported and strengthened by an internal framework of hollow chitinous tubes. The veins. — The so-called "veins" or "nervures," which are situ- ated between the upper and under layers of the wing are so disposed as to give the greatest lightness and strength to the wings. Hagen has shown that in the freshly formed wings these two layers can be separated, when it can be seen that the veins pass through each layer. These veins are in reality quite complex, consisting of a minute central trachea enclosed within a larger tube which at the instant the insect emerges from the nymph, or pupa, as the case may be, is filled with blood (Fig. 136). Since these tubes at first contain blood, which has been observed to circulate through them, and since the heart can be most easily injected through them, they may more properly be called veins than nervures. The shape and venation of the wings afford excellent ordinal as well as family and generic characters, while they also enable the systematist to exactly locate the spots and other markings of the wings. The spaces enclosed by the veins and their cross-branches are called cells, and their shape often affords valuable generic and specific characters. The structure of a complete vein is described by Spuler. In a cross-section of a noctuid moth (TripJiwna pronuba, Fig. 136) the chitinous walls are seen to consist of two layers, an outer (u) and inner (c), the latter of which takes a stain and lies next to the hypodermis (hy). In the cavity of the vein is the trachea (tr~), which shows more or less distinctly the so-called spiral thread; within the cavity are also Semper's " rib " (r) and blood-corpuscles hy V FIG. 136. —Cross-section of \\ing Fio. 137. — Cross-section of wing of Pirns : .«, insertions of Pronuba. — At'u-r Spuler. of scales. —After Spuler. (be), which proves that the blood circulates in the veins of the com- pletely formed wing, though this does not apply to all Lepidoptera with hard mature wings. We have been able to observe the same structure in sections of the wing of Zygaena. 122 TEXT-BOOK OF ENTOMOLOGY A cross-section of a vein of Picris brassicce shows that the large trachea is first formed, and that it extends along the track between the protoplasmic threads connecting the two hypodermal layers. The main tracheae throw off on both sides a number of secondary branches showing at their end a cell with an iiitracellnlar tracheal structure ; these accessory tracheae afterwards branch out. The acces- sory or transverse tracheae often disappear, though in some moths they remain permanently. Fig. 137 tr2 represents these secondary veins in the edge of the fore wing of Laverna vanella, arising from a main trachea (tr) passing through vein I (v), two of the twigs extending to the centre, showing that the latter has no homology with a true vein. Only rarely and in strongly developed thick folds are the transverse tracheae provided with a chitinous thickening, as for example in Cossus ligniperda. Since from such accessory tracheae the transverse veins in lepidopterous wings are developed, we can recognize in them the homologies of the net-veins in reticulated venations. There is no sharply defined difference between reticulated and non- reticulated venations ; no genetic difference exists between the two kinds of venation, since there occur true Blattidae both with and without a reticulated venation (Spuler). In the fore wings of Odonata, Psocina, Mantispidge, and most Hymenoptera is an usually opaque colored area between the costal edge and the median vein, called the pterostigma. In shape the wings are either triangular or linear oval, and at the front edge the main veins are closer together than elsewhere, thus strengthening the wings and affording the greatest resistance to the air in making the downward stroke during flight. It is noticeable that when the veins are in part aborted from partial disuse of the wings, they disappear first from the hinder and middle edge, those on the costal region persisting. This is seen in the wings of Embiidce (Oligotoma), Cynipidae, Proctotrupidee, Chalcids, ants, etc. The front edge of the wing is called the costal, its termination in the outer angle of the wing is called the apex ; the outer edge (termen) is situated between the apex and the inner or anal angle, between which and the base of the wing is the inner or internal edge. \Yliile in Orthoptera, dragon-flies, Termitidae, and Neuroptera the wings are not attached to each other, in many Lepidoptera they are loosely connected by the loop and frenulum, or in Hymenop- tera by a series of strong hooks. These hooks are arranged, says Newport, " in a slightly twisted or spiral direction along the margin of the wing, so as to resemble a screw, and when the wings are expanded attach themselves to a little fold on the posterior mar- THE Jl'dl'M AND SQUAMAE 123 gin of the anterior wing, along which they play very freely when the wings are in motion, slipping to and fro like the rings on the rod of a window curtain." At the base of the hind wings of Trichoptera and in the lepi- dopterous Micropteryx there is an angular fold (jugum) at the base of each wing (Fig. 138) ; that of the anterior wings is retained in Eriocephala and Hepialidae. In the wings of Orthoptera as well as other insects, the fore wings, especially, are divided into three well-marked areas, the cos- FIG. 138. — Venation of fore and hind wings of Micropteryx purpnrrlta : ;;, jugum, on each wing; d, discal vein ; the Koiuan numerals indicate veins I. -VIII. and their branches. tal, median, and internal ; of these the median area is the largest, and in grasshoppers and crickets is more or less modified to form the musical apparatus, consisting of the drum-like resonant area, with the file or bow. The squamae. — In the calyptrate Muscidse, a large scale-like mem- branous broad orbicular whitish process is situated beneath the base of the wing, above the halter; (Fig. 94, 10 sg.~) it is either small or wanting in the acalyptrate rnuscids. Kirby and Spence state that when the insect is at rest the two divisions of this double lobe are folded over each other, but are extended during flight. Their exact use is unknown. Kolbe, following other German authors, considers the term squama as applicable to the whole structure, restricting the term alula to the other lobe-like division. 124 TEXT-BOOK OF ENTOMOLOGY More recently (1896 and 1897) Osten-Sacken recommends " squama in the plural, as a designation for both of these organs taken together ; squama, in the singular, would mean the posterior squama alone, and antisquama the anterior squama alone;" the strip of membrane running in some cases between them, or connecting the squama with the scutellum, should be called the post-alar membrane. 15y a mistake Loew, and others following him, used the word (i-ijnla for squama, but this term should be restricted to the sclerite of the meso- thnrax previously so designated (Fig. 90, A,t) . The squama or its two subdivisions has also by various authors been termed alula, calypta, squamula, lobulus, axillary lobe, aileron, cuilleron, schuppen, and scale. (Berlin Ent. Zeitschrift, xli, 1890, pp. 285-288, 328, 338.) The halteres. — In the Diptera the hind wings are modified to form the halteres or balancers, which are present in all the species, even in Xycteribia, but are absent in Branla. Meinert finds structures in the Lepidoptera which he considers as the hoino- logues of the halteres of Diptera. "In the Noctuidse," he remarks, "I find arising from the fourth thoracic segment (segment me"diaire), but covered by hair, an organ like the halter of Diptera." (Ent. Tidskrift., i, 1880, p. 1G8.) He gives no details. In the Stylopidee, on the contrary, the fore wings are reduced to little narrow pads, while the hind wings are of great size. The thyriditim is a whitish spot marking a break in the cubital vein of the fore wing of Trichoptera ; these minute thyridia occur in the fore wings of the saw-flies ; there is also an intercostal thyri- dium on the costal part of the wings of Bermaptera. The fore wings of (Mhoptera are thicker than the hinder ones, and serve to protect the hind-body when the wings are folded ; they are sometimes called tegmuia. It is noteworthy, that, according to Scudder, in all the paleozoic cockroaches the fore wings (tegmina) were as distinctly veined as the hinder pair, " and could not in any sense be called coriaceous." (Pretertiary Insects of N. A., p. 39.) Scudder also observes that in the paleozoic insects as a rule the fore and hind wings were similar in shape and venation, "heterogeneity making its appearance in mesozoic times." In the heteropterous Hemiptera, also, the basal half of the fore wings is thick and cori- aceous or parchment-like, and also protects the body when they are folded ; these wings are called ltcnn'/;/tr/'/i/<'tinnit, being wide in the Tene- brioimUe. During night " the elytra are opened so as to form an THE ELYTRA 125 angle with the body and admit of the free play of the wings" (Kirby and Spence). In the running beetles (Carabidae), also in the weevils and in many Ptinidae, the hind wings are wanting, through disuse, and often the elytra are firmly united, forming a single hard shell or case. The firmness of the elytra is due both to the thick- ness of the chitinous deposit and to the presence of minute chitinous rods or pillars connecting the upper and lower chitinous surfaces. Hoffbauer finds that in the elytra of beetles of different families the venation characteristic of the hind wings is wanting, the main tracheae being irregular or arranged in closely parallel longitudinal lines, and nerve-fibres pass along near them, sense-organs being also present. The fat-bodies in the cavity of the elytra, which is lined with a matrix layer, besides nerves, tracheae, and blood, contain se- cretory vesicles filled with uric-acid concretions such as occur in the u FIG. 139. —Longitudinal section through the edge of the elytrum of Lina (?nea : gl, glands; r, reservoir; fb, fat-body ; m, matrix ; >i, upper, — /, lower, lamella. — After Hoffbauer. fat-body of Lampyris. There are also a great many glands varying much in structure and position, such occurring also in the pronotum (Fig. 139). Meinert considers the elytra of Coleoptera to be the homologues of the tegulte of Lepidoptera and of Hymenoptera. He also calls attention to the alula observed in Dyticus, situated at the base of the elytra, but which is totally covered by the latter. The alulte of these beetles he regards as the homologues of the anterior wings of Hymenoptera and Diptera. No details are given in support of these views. (Ent. Tidskrift, i, 1880, p. 168.) Hoffbauer (181)2) also has suggested that the elytra are not the homologues of the fore wings of other insects, but of the tegula-. Kolbe describes the alula of Dyticus as a delicate, membranous lobe at the base of the elytra, but not visible when they are closed : its fringed edge in Dyticus is bordered by a thickening forming a tube which contains a fluid. The alula is united with the inner basal portion and articulation of the wing- cover, forming a continuation of them. Diifmir considered that the humming noise made by these beetles is produced by the alulets. Hoffbauer finds no structural resemblances in the alulse of Dyticus to the elytra. He does not find "the least trace of veins." They are more like ap- pendages of the elytra. Lacordaire considered that their function is to prevent 120 TEXT-BOOK OF ENTOMOLOGY the disarticulation of the elytra, but Hoffbauer thinks that they serve as con- trivances to retain the air which the beetle carries down with it under the sur- face, since he almost always found a bubble of air concealed under it ; besides, their folded and fringed edge seems especially fitted for taking in and retaining air. Hoffbauer then describes the tegulse of the hornet and finds them to be, not as Cholodkovsky states, hard, solid, chitinous plates, but hollow. They are inserted immediately over the base or insertion of the fore wings, being articu- lated by a hinge-joint, the upper lamella extending into a cavity of the side of the mesothorax, and connected by a hinge-like, articulating membrane with the lower projection of the bag or cavity. The lower lamella becomes thinner towards the place of insertion, is slightly folded, and merges without any articu- lation into the thin, thoracic wall at a point situated over the insertion of the fore wing. The tegulas also differ from the wings in having no muscles to move them, the actual movements being of a passive nature, and due to the upward and downward strokes of the wings. Comstock adopts Meinert's view that the elytra are not true fore wings, but gives no reasons. (Manual, p. 495.) Dr. Sharp,1 however, after examining Dyticus and Cybister, affirms that this structure is only a part of the elytron, to which it is extensively attached, and that it corresponds with the angle at the base of the wing seen in so many insects that fold their front wings against the body. He does not think that the alula affords any support to the view that the elytra of beetles correspond with the tegulfe of Hymenoptera rather than with the fore wings. That the elytra are modified paraptera (tegulse) is negatived by the fact that the latter have no muscles, and that the elytra contain trachea? whose irregular arrangement may be part of the modified degenerate structure of the elytra. Kolbe finds evidences of veins. The question may also be settled by an ex- amination of the structure of the pupal wings. A study of a series of sections of both pairs of wings of the pupa of Doryphora and of a Clytus convinces us that the elytra are the homologues of the fore wings of other insects. e. Development and mode of origin of the wings Embryonic development of the wings. - - The wings of insects are essentially simple dorsal outgrowths of the integument, being evagi- nations of the hypoclermis. They begin to form in the embryo before hatching, first appearing as folds, buds, or evaginations, of the hypo- dermis, which lie in pouches, called peripodal cavities. They are not visible externally until rather late in larval life, after the insect, such as a grasshopper, has moulted twice or more times; Avhile in holometabolous insects they are not seen externally until the pupa state is attained. The subject of their origin is in a less satisfactory state than de- sirable from the fact that at the outset the development of the wings of the most generalized insects, such as Orthoptera, Termes, etc., was not first examined, that of the most highly modified of any insects, i.e. the Museida\ having actually been first studied. 1 Proo. Ent. Sue. London. Feb. 19, ls'M>. Heymons also shows that the germs of the elytra of the larva of T ino/itor in the prepupal stage arc like those of other insects. (Sit/ungs-Ber. Gesell. uatur f. Freunde zu Berlin, 18%, pp. 142-144.) EMBRYONIC GROWTH OF THE WINGS 127 In the course of his embryological studies on the Muscidse (Musca rnmitoria and Sarcophaga ci(rnarla) Weisinann (1864) in examining the larvae of these flies just before pupation, found that the wings, as well as the legs and mouth-appendages, developed from micro- scopic masses of indifferent cells, which he called " imaginal discs." From the six imaginal discs or buds in the lower part of the thorax arise the legs, while from four dorsal discs, two in the meso- and two in the metathoracic segment, arise the fore and hind wings (Fig. 141.) These imaginal buds, as we prefer to call these germs, usually appear at the close of embryonic life, being found in freshly hatched larvae. As first observed by Weismann, the buds are, like those of the appendages, simply attached to tracheae and sometimes to nerves, Fro. 140. — Imaginal buds in Musca, — A, in Corethra, — B, in Melophagus, — /, nervous cord. showing their connection with the hypodermis, which has been torn away during the process of cutting. That the wing is but a fold of tin- hypodermis is well seen in Fig. 144, of Datana, which represents a much later stage of development than in Figs. 142 and 143, the larva just entering on the semipupa stage. In caterpillars of stage I, 3 to 4 mm. in length, Gonin found the wing-germs as in Fig. 14r>. A being a thickening of the hypodermis, with the embryonic cells, i.e. of Verson, on the convex border. The two leaves, or sides of the wing, begin to differentiate in stage II (C, Z)), and in stage I I 1 the envelope is formed (E), while the tracheae begin to proliferate, and the capillary tracheae or tracheoles at this time arise (Fig. 145, tc). The wall of the principal trachea EMBRYONIC GROWTH OF THE 131 appears to be resolved into filaments, and all the secondary branches assume the appearance of bundles of twine. Landois regarded tln-m as the product of a transformation of the nuclei, but Gonin thinks they arise from the entire cells, stating that from each cell arises a ball (peloton) of small twisted tubes. As the large branches penetrate into the wing, the balls (pelotons) of tine tracheal threads tend to unroll, and each of the new ramifica- tions of the secondary tracheal system is accompanied in its course by a bundle of capillary tubes. This secondary system of wing- tracheae, then, arises from the mother trachea at the end of the third Fio. 144. — Section through mesothorade segment of Datann tninixtru. passing throuirh the wings (TI: <•, cutii-iila : ti>/p. hvpodermis ; . apodenu- ; dm, dorsal longitudinal, —ww, ventral longitudinal, muscles: ihiit, depressor musHr cif tergum ; t, trachea; «, nerve cords; /.intes- tine ; n, urinary tubes ; /, insertion of legs. stage, when we find already formed the chitinous tunic, which Avill persist through the fourth stage up to pupation. It differs from the tracheoles in not communicating with the air-passage; it possesses no spiral membrane at the origin, and takes no part in respiration. Gonin thus sums up the nature of the two tracheal systems in the rudimentary wing, which he calls the provisional and permanent systems. " The first, appearing in the second stage of the larva, com- prises all the capillary tubes, and arising from numerous branches passes off from the -lateral trunk of the thorax before reaching the wing ; the second is formed a little later by the direct ramification of the principal branch. 132 TEXT-BOOK OF ENTOMOLOGY " These two systems are absolutely independent of each other within the wing. Their existence is simultaneous but not conjoint. One is functionally active after the third moult ; the other waits the rinal transformation before becoming active." Evagination of the wing outside of the body. - - We have seen that the alary germs arise as invaginations of the hypodermis ; we will now, with the aid of Gonin's account, briefly describe, so far as is known, the mode of evagination of the wings. During the fourth and last stage of the caterpillar of Pieris, the wings grow very rapidly, and undergo important changes. Six or seven days after the last larval moult the chitinous wall is formed, the wing remaining trans- parent. It grows rapidly and its lower edge extends near the legs. It is now much crumpled on the edge, owing to its rapid growth within the limits of its own seg- ment. Partly from being somewhat re- tracted, and partly owing to the irregu- larity of its surface, the Aving gradually separates envelope, cavity of tion (Fig. FIG. 145. — A, section of wing-bud of larva of Picrix />m.v,v/V, behind it, making the bud appear independent of the thoracic wall. E, wing-bud at the beginning of the 8<1 larval stage, section passing almost through the pedicel or hypodermic, insertion, the traces of which appear at/f (' ; h, hypodermis ; / or t>; trachea ; /, opening of in vaginal ion ; «•<•, embryonic, cells; /, external layer or envelope; /;/, internal wall of the wing; *•,/', external wall; ft, cell of a tactile hair; tc, capillary tubes; c, cavity of invagination. — After Gonin. from its and the in vagina- 145, c) becomes more like a distinct or real space. The outer opening of the alary sac enlarges quite plainly, though without reaching the level of the edge of the wing. This condition of things does not still exactly explain how the wing passes to the outside of the body. Gonin compares these ron- ditions to those exhibited by a series of sections of the larva, made forty-eight hours later, on a caterpillar which had just spun its girdle of silk. At this time the wings have become entirely external, but, HOW THE WIXGS GET OUTSIDE OF THE BODY 133 says Gonin, we do not see the why or the how. The partition of the sac has disappeared, and with it the cavity and the leaf of the envelope. It appears probable that the partition has been destroyed, because the space between the two teguments is strewn with numerous bits, many of which adhere to the chitinous integument, while others are scattered along the edges of the wings, in their folds, or between the wings and the wall of the thorax. Another series of sections showed that the exit of the fore wings had been acco'mplished, while the hinder pair was undergoing the process of eversion. In this case the partition showed signs of degeneration : deformation of the nuclei, indistinct cellular limits, pigmentation, granular leucocytes, and fatty globules. After the destruction of the partition, what remains of the layer of the envelope is destined to make a part of the thoracic wall and undergoes for this purpose a superficial desquamation. The layer of flattened cells is removed and replaced by a firmer epithelium like that covering the other regions. It is this renewed hypodermis which conceals the wing within, serves to separate it from the cavity of the body, and gives the illusion of a complete change in its situa- tion. Other changes occur, all forming a complete regeneration, but which does not accord with the description of Van Rees for the Muscidse. Finally, Gonin concludes that the de'bris scattered about the wing comes from the two layers of the partition of the sac, from the flattened hypodermis of the renewed envelope, from the chitinous cuticle of the wing, and from the inner surface of the chitinous integument. He thinks that the metamorphosis of Pieris is intermediate between the two types of Corethra and of Musca, established by Weismann, as follows: Corethra. — The wing is formed in a simple depression of the hypodermic wall. No destruction. Pieris. — The rudiment is concealed in a sac attached to the hypodermis by a short pedicel. Destruction of the partition and its replacement by a part of the thoracic wall by means of the imaginal epithelium. Musca. — The pedicel is represented by a cord of variable length, whose cavity may be obliterated (Van Rees). The imaginal hypodermis is substituted for the larval hypodermis, which has completely disappeared, either by desquama- tion (Viallanes), or by histolytic resorption (Van Rees). Extension of the wing ; drawing out of the tracheoles. — When it is disengaged from the cavity, the wing greatly elongates and the creases on its surface are smoothed out ; the blood penetrates between the two walls, and the cellular fibres, before relaxed and sinuous, are now firmly extended. Of the two trachea! systems, the large branches are sinuous, and they are rendered more distinct by the presence of a spiral mem- brane ; but the two tunics are not separated as in the other tracheae of the thorax ; moreover, the mouth choked up with debris does not yet communicate with that of the principal trunk. The bundles of tracheoles on their part form straight lines, as if the folds of the organ had had no influence on them. As they have remained bound together, apart from the chitinous membrane of the tracheal trunk, 134 TEXT-BOOK OF ENTOMOLOGY they become drawn out with this membrane, at the time of exuvia- tion, i.e. of pupation, and are drawn out of the neighboring spiracle. "This is a very curious phenomenon, which can be verified experimentally: if we cut off the wing, while sparing the larval integument around the thoracic FIG. 146. — Full-grown larva of Pltris ItramficcB, opened along- the dorsal line: d, digestive canal; x, silk-gland ; (/, brain; xl 7, prothoraoic stigma; ntlV, 1st abdominal stigma; u, ), and wings (/, A-C), and afterwards their evaginatioh D, so that they lie on the outside of the body. E, stage B, showing the hypodernial cavities (/) and stalks connecting the germs with the hypodermis (s). — After Graber. wing of a mature larva and shows the rudiment of the wing, lying in its hypodermal pocket or peripodal cavity. How the trachea passes into the rudimen- tary wing, and eventually becomes divided into the branches, around which the main veins afterwards form, is seen in Figs. 144, 147, ir>(.). The histological condi- tion of the wing at this time is represented by Fig. 1-n;. 1 111. >iTtion lengthwise through the left wing L J of mature larva In l'i,-rix fti/nr: t, trachea; hyp, hypo- 151, the Spindle-like hypo- (Ic-nnis ; c, cutirula. — After Mayer. dermal cells forming the two walls being separated by the ground-membrane of Semper. " While in the pupa, state," says Mayer, " the wing-membrane is thrown into a very regular series of closely compressed folds, a single scale being inserted upon the crest of each fold. When the butter- HOW THE WINGS ENLARGE 137 fly issues from the chrysalis, these folds in. the pupal wings flatten out, and it is this flattening which causes the expansion of the wings. ... It is evident that the wings after emergence undergo a great stretching and flattening. The mechanics of the operation appears to be as follows. The haemolymph, or blood, within the wings is under considerable pressure, and this pressure would naturally tend to enlarge the freshly emerged wing into a balloon- shaped bag ; but the hypodermal fibres (/*) hold the upper and lower walls of the wing-membrane closely together, and so, instead of becoming a swollen bag, the wing becomes a thin flat one. And ^ eta Kdrtu f¥fWWWr//J i Lli 1 Ltkl n *4i ^^ \ -X, j.'f- • \ m/j f I wfFrFf drm* 'IJ II4«- WJ FIG. 150. — Diagrammatic reproduction of Fig-. 149 FIG. 151 . — Section of the wing-prenn, the showing the wing-ifenn in its perijiodal cavity (p): upper and lower sides connected by spindle- Ji'drin, hyi>o(lcnni> ; //•. traclii-a ; ctti, cuticula ; a, like hypodermic cells (%), forming the rods anterior end. — After Mayer. of the adult wing ; mtir, ground-membrane of Semper. — After Mayer. thus it is that the little thick corrugated sac-like wings of the freshly emerged insect become the large, thin, flat wings of the imago. . . . The area of the wing of the imago of Danais plexippus is 8.G times that of the pupa. Xow, as the wing of the young pupa has about 60 times the area of the wing in the mature larva, it is evident that in passing from the larval state to maturity the area of the wings increases more than 500 times." /. The primitive origin of the wings Farther observations are needed to connect the mode of formation of the wings in the holometabolous insects with the more primitive mode of origin seen in the hemimetabolous orders, but the former mode is evidently inherited from the latter. Pancritius remarks that the development of the rudiments of the wing in a hypodermal cavity is in the holometabolic insects to be regarded as a later inherited character, the external conditions causing it being un- known. 138 TEXT-BOOK OF ENTOMOLOGY Fritz Miiller was the first to investigate the mode of development of the wings of the hemimetabolic insects, examining the young nymphs of Termites. He regards the wings as evaginations of the hypodermis, which externally appear as thoracic scale-like projec- tions, into which enter rather late in nymphal life tracheae which correspond to the veins which afterward arise. The primitive mode of origin of the wings may, therefore, be best understood by observing the early stages of those insects, such as the Orthoptera and Hemiptera, which have an incomplete metamor- phosis. If the student will examine the nymphs of any locust in their successive stages, he will see that the wings arise as simple expansions downward and backward of the lateral edges of the meso- and metanotum. In the second nymphal stage this change begins to take place, but it does not become marked until the succeeding stage, when the indications of veins begin to appear, and the lobe- like expansion of the notuni is plainly enough a rudimentary wing. Graber l thus describes the mode of development of the wings in the nymph of the cockroach : " If one is looking only at the exterior of the process, he will perceive sooner or later on the sides of the meso- and ineta- thorax pouch-like sacs, which increase in extent with the dorsal integument and at the same time are more and more separated from the body. These wing- covers either keep the same position as in the flat-bodied Blattidse, or in insects with bodies more compressed the first rudiments hang down over the sides of the thorax. As soon as they have ex- ceeded a certain length, these wing-covers are laid over on the back. However, if we study the process of development of the wings with a microscope, by means of sections made obliquely through the FIG. 152. — Rudimentary wine of youns thorax, the process appears still more nymph of Blatta, with the five principal veins simple. The chief force of all evolution is and remains the power of growth in a definite direction. In regard to the skin this growth is possible in insects only in this way ; namely, that the outer layer of cells is increased by the folds which are forced into the superficial chitinous skin. These folds naturally grow from out- moult to another in proportion to the multiplication of the cells, and are not smoothed out until after the moulting, when the outer resistance is over- come. 1 ZurEntwiekelungsgeschichte uinl Reproductionsfahigkeit der Orthopteren. Von Vitus Graber. Sit/imgsfoerichte <1. niatli.-naturw. Classe der Akad. d. Wisseusch., Wien. Bd. Iv, Abth. i, 1807 ; also Die lusekten. THE PRIMITIVE ORIGIN OF THE WINGS 139 "As. however, the first wing-layers depend upon the wrinkling of the general integument of the body through the increase in the upper layer, the further growth of the wings depends in the later stages upon the wrinkling of the epi- dermis of the wing-membrane even, which fact we also observe under the microscope when the new wings drawn forth from the old covers appear at Fio. 153. — Partial metamorphosis of Melanoplux femnr-rubrum, showing the five nymph stages, and the gradual growth of the wings, which are first visible externally in 3, Bl>, 3c. — Emerton 140 TEXT-BOOK OF ENTOMOLOGY first to be quite creased together. These wing-like wrinkles in the skin are not empty pouches, but contain tissues and organs within, which are connected with the skin, as the fat of the body, the net- work of tracheae, muscles, etc. Alongside the tracheae, running through the former wing-pouches and accom- panied by the nerves, there are canals through which the blood flows in and out. A B -n Fio. 154. FIG. 155. Fio. 154. — Stapes in the growth of the wings of the nymph of T&rmes flavipes : A, young ; n, a wins i-nl:irgiMl. It. older nymph ; l>, tore wing ; n, a vein. O, wings more advanced ; — />, mature. Fio. 155. — Wings of nymph of 1'socus. " After the last moult, however, when the supply of moisture is very much re- duced in the wing-pouches, which are contracted at the bottom, their two layers become closely united, and afterward grow into one single, solid wing-membrane. "These thick-walled blond-tubes arising above and beneath the upper and lower membrane of the wing are the veins of the wings ; the development of ORIGIN OF THE WINGS IN LOCUSTS, BUGS, ETC. 141 the creased wings in the pupa of butterflies is exactly like that of cockroaches and bugs. The difference is only that the folds of integument furnishing the wings with an ample store of material for their construction reach in a relatively shorter time, that is the space of time between two moults, the same extent that they would otherwise attain only in the course of several periods of growth in the ametabolous insects. Ignorant of Graber's paper, we had arrived at the same result, after an examination of the early nymph-stages of the cockroach, as well a"s the locusts, Termites, and various Hemiptera. In all these forms it is plainly to be seen that the wings are simply expansions, FIG. 156. — Nymph of Aph rophora perinutata, with enlarged view of the wings and the veins : pro, pronotum ; sc, mesoscutuiu ; \iit>, 1st abdominal segment. either horizontal or partly vertical (where, as in locusts, etc., the body is compressed, and the meso- and metanota are rounded down- wards), of the hinder and outer edge of the meso- and metanotum. As will be seen by reference to the accompanying figures, the wings are notal (tergal) outgrowths from the dorsal arch of the two hinder segments of the thorax. At first, as seen in the young pupal cock- roach (Fig. 152) and locust (Fig. 153, also Figs. 154 and 156) the rudi- ments of the wings are continuous with the notum. Late in nymphal life a suture and a hinge-joint appear at the base of the wing, and thus there is some movement of the wing upon the notum ; finally, the tracheae are well developed in the wings, and numerous small sclerites are differentiated at the base of the wing, to which the 11-J TEXT-BOOK OF ENTOMOLOGY special muscles of flight are attached, and thus the wings, after the last nymphal moult, have the power of flapping, and of sustaining the insect in the air ; they thus become true organs of flight. It is to be observed, then, that the wings in all hemimetabolous insects are outgrowths from the notum, and not from the flanks or pleurum of the thorax. There is, then, no structure in any other part of the body with which they are homologous. The same may be said of the true Neuroptera, Trichoptera (Fig. 157), the Coleoptera, and the Diptera, Lepidop- tera, and Hymenoptera. As we have observed in the house fly,1 the wings are evidently outgrowths of the meso- and metanotum ; we have also observed this to be most probably the case in the Lepidoptera, from observations on a Tortrix in different stages of meta- morphosis. It is also the case with the Hymenoptera, as we have observed in. bees and wasps ; 2 and in these forms, and probably all Hymenoptera, the wings are outgrowths of the scutal FK;. 1ST. — Development of wings of region of the notum. Trichoptera: 4, portion of body-wall of young larva of Trichostegia ; cA.cuticuia, With these facts before us we may forming at >• a projection into the hypo- . . „ d.Tiiiis. m -, i', and ft, forming thus' the speculate as to the probable origin oi first rudiment of the wing. Jf, the parts in . „ . , , ,, a larva of nearly full size; «, c, d, b, the the WlUgS Of insects. Hie V16WS held well-developed hypodermis of the wing- r> r~\ germ separated fnto two parts iiy r, the by some are those oi (jregenoaur, also penetrating extension of the cuticula ; r, , , T , , -, , . . •,-, , mesoderm. a wing-pad of another Phry- adopted by Lubbock, and originally by ganeid freed from its case at its change to 1 p , . 1 . ,-*, , the pupa : /,. ,/, outer layer of the hypo- myself / According to Gegenbaur : derniis (mi of the body-wall; v, inner layer within nuclei. — After Dewitz, from "The wings must be regarded as homolo- gous with the lamellar tracheal gills, for they do not only agree with them in origin, but also in their connection with tin- bn6. 8 Our Common Insects, 187^, p. 171. THE WINGS NOT DERIVED FROM TR AC HEAL GILLS 14:5 If we examine the tracheal gills of the smaller dragon-fly (Agrion), or the May-flies, or Sialidse, or Perlidae, or Phrygaiieidse, we see that they are developed in a very arbitrary way, either at the end of the abdomen, or on the sternum, or from the pleurum; moreover, in structure they invariably have but a single trachea, from which minute twigs branch out ; 1 in the wings there are five or six main trachea?, which give rise to the veins. Thus, in themselves, irre- specti,ve of their position, they are not the homologues of the gills. The latter are only developed in the aquatic representatives of the Neuroptera and Pseudo- neuroptera, and are evidently adaptive, secondary, temporary organs, and are in no sense ancestral, primitive structures from which the wings were developed. There is no good reason to suppose that the aquatic Odonata or Ephemerids or Neuroptera were not descend- ants of terrestrial forms. To these results we load arrived by a review of the above-mentioned facts, before meeting with Fritz Miiller's opinions, derived from a study of the development of the wings of Calotermes (Fig. 158). Muller 2 states that " (1) The wings of insects have not originated from ' tracheal gills.' The wing-shaped continuations of the youngest larvae are in fact the only parts in which air tubes are completely wanting, while trachea? are richly developed in all other parts of the body.3 (2) The wings of insects have arisen from FIG. 158. — Changes in external form of the newly hatched, with 9 antennal joints, x 8. Jj, older larva, with 10 joints, x 8. C, next stag-e. with 11 joints, x s. D, larva, with twelve joints ; the position of tin1 parts of the alimentary canal are shown : i\ crop; in, stomach; 1>. "paunch"; e. intestine; r, heart, x ^. — After Fritz Miiller, from Sharp. 1 Compare the observations of Palmen, Gerstacker, Vayssiere, and others. 2 Beitrage zur Kenntniss der Termiten. Jenaische Zeitschrift fiir Naturwissen- chaft, Bd. ix, Heft 2, p. 253, 1875. Compare, however, Palmen's Zur Morphologie des Tracheensystems, Helsingfors, 1877, wherein he opposes Miiller's view and adopts Gegenbaur's. See p. 8, foot-note. 8 Pancritius, who also adopted Miiller's views, lays much stress on the fact that in larva? of some orders the tracheae do not enter the rudimentary wings until the end of larval life, and hence the wings have not originated from tracheal gills, but were originally " perhaps only protective covers for the body." 144 TEXT-BOOK OF ENTOMOLOGY lateral continuations of the dorsal plates of the body-segments with which they are connected." Now, speculating on the primary origin of wings, we need not suppose that they originated in any aquatic form, but in some ancestral land insect related to existing cockroaches and Termes. We may imagine that the tergites (or notum) of the two hinder segments of the thorax grew out laterally in some leaping and running insect ; that the expansion became of use in aiding to sup- port the body in its longer leaps, somewhat as the lateral expansions of the body aid the flying squirrel or certain lizards in supporting the body during their leaps. By natural selection these structures would be transmitted in an improved condition until they became flexible, i.e. attached by a rude hinge- joint to the tergal plates of the meso- and metathorax. Then by continued use and attempts at flight they would grow larger, until they would become perma- nent organs, though still rudimentary, as in many existing Orthoptera, such as certain Blattarise and Pezotettix. By this time a fold or hinge having been established, small chitinous pieces enclosed in membrane would appear, until we should have a hinge flexible enough to allow the wing to be folded on the back, and also to have a flapping motion. A stray tracheal twig would naturally press or grow into the base of the new structure. After the trachea running towards the base of the wing had begun to send off branches into the rudimen- tary structure, the number and direction of the future veins would become determined on simple mechanical principles. The rudimentary structures beat- ing the air would need to be strengthened on the front or costal edge. Here, then, would be developed the larger number of main veins, two or three close together, and parallel. These would be the costal, subcostal, and median veins. They would throw out branches to strengthen the costal edge, while the branches sent out to the outer and hinder edges of the wings might be less numerous and farther apart. The net-veined wings of Orthoptera and Pseudoneuroptera, as compared with the wings of Hymenoptera, show that the wings of net-veined insects were largely used for respiration as well as for flight, while in beetles and bees the leading function is flight, that of respiration being quite subordi- nate. The blood would then supply the parts, and thus respiration or aeration of the blood would be demanded. As soon as such expansions would be of even slight use to the insect as breathing organs, the question as to their perma- nency would be settled. Organs so useful both for flight and aeration of the blood would be still further developed, until they would become permanent structures, genuine wings. They would thus be readily transmitted, and being of more use in adult life during the season of reproduction, they -would be still further developed, and thus those insects which could fly the best, i.e. which had the strongest wings, would be most successful in the struggle for existence. Thus also, not being so much needed in larval life before the reproductive organs are developed, they would not be transmitted except in a very rudi- mentary way, as perhaps masses of internal indifferent cells (imaginal discs), to the larva, being the rather destined to develop late in larval and in pupal life. Thus the development of the wings and of the generative organs would go hand in hand, and become organs of adult life.1 The development and structure of the tracheae and veins of the wing. — The so-called veins ("nervures") originate from tine tracheal 1 Reproduced from the author's remarks in Third Report U. S. Eut. Commission, pp. 2G8-271, 1883. DEVELOPMENT OF THE TRACHEAE AND VEINS 145 twigs which pass into the imaginal discs. A single longitudinal trachea grows down into the wing-germ (Fig. 147), this branch aris- ing through simple budding of the large body-trachea passing under the rudiment of the wing. Gonin states that before the tracheae reach the wing they divide into a great number of capillary tubes united into bundles and often tangled. This mass of 'tracheae does not penetrate into the wing-germ by one of its free ends, but spread- ing over about a third of the sur- face of the wing, separates into a dozen bundles which spread out fan-like in the in- terior of the wing. (Fig. 159). These ramifications, as seen under the mi- croscope, are very irregular; they form here and there knots and anastomoses. They end abruptly in tufts at a little dis- tance from the edge of the wing. A raised semicir- cular ridge (6) surrounds the base of the wing, and within this the capillaries are formed, while on the other side they are covered by a cellular layer. Landois, he says, noticed neither the pedicel of the insertion of the wing (i) nor the ridge (6). Herold only states that the trachese pass like roots into the wing. Landois believed that they formed an integral part of it, Dewitz and Pancritius used sections to determine their situation. Fig. 160 will illustrate Landois' views as to the origin of the trachese and veins. A represents the germ of a hind wing attached FIG. 159. — Germ of a hind wing detached from its insertion, and examined in glycerine: •/, pedicel of insertion to the hypoder- mis ; t>; trachea ; b~ semicircular pad ; e, enveloping membrane ; c, bundle of capillary tracheoles ; the large trachea? of the wing not visible ; they follow the course of the bundles of tracheoles. — After Gonin." 146 TEXT-BOOK OF ENTOMOLOGY u< FIG. 160.— Origin of the wings and their veins. —After Landois. to a trachea ; c the elongated cells, in which, as seen at B, c, a fine tangled tracheal thread (£) appears, seen to be magnified at C. The cell walls break down, and the threads become those which pass through the centre of the veins. The wing-rods. — Semper discov- ered in transverse sections of the wings, what he called Fliigelrippen ; one such rib accompanying the trachea in each vein. He did not discover its origin, and his descrip- tion of it is said to be somewhat erroneous. Scliaeffer has recently examined the structure, remarking : " I have surely observed the connection of this cellular tube with the tracheae. It is found in the base of the wing where the lumen of the tracheae is much widened. I only describe the fully formed rib (rif>pe). In a cross-section it forms a usually cylindrical tube which is covered by a very thin chitiuous intima which bears deli- cate twigs (Fig. 161). These twigs are analogous to the thickened ridge of the tracheal intima. I Can 866 11O connection be- tween the branches of the differ- ent twigs. Through the ribs (I'ippeii) extend a central cord (c) which shows in longitudi- nal section a clear longitudinal streaking. Semper regarded it as a nerve. But the connection of the tube with the trachea con- tradicts this view. I can only regard the cord as a separation- product of the cells of the walls." Other historical elements. - T^poo qvp tV.p hi nod IvrmYh rnv L-lvmPn> l puscles, blood-building masses, and nerves. Scliaeffer states that in the immature pupal wings we find besides the large tracheae, which are more or less branched, Fl«- lei. — Section of the "rib " of a vein : o, cord; 6, twig. — After Schaetter. FIG. 162. -Parts of a vein of the cockroach, showing the nerve («) by the side of the trachea (tr); o, blood-corpuscles. — After Moseley. THE BLOOD, ETC., IN THE WING-VEINS 147 and in the wing-veins at a later period, blood-corpuscles which are more or less gorged with nutritive material, and also the "balls of granules ?' of Weismann, which are perhaps the " single fat-body cells " detected by Semper. Schaeffer also states that into the hypodermal fold of the rudiments of the wings pass peculiar forma- tions of the fat-body and traclieal system, and connected with the fat-body are masses of small cells which by Schaeffer are regarded as blood-building masses. Fine nerves have also been detected within the veins, Moseley stating that a nerve-fibre accompanies the trachea in all the larger veins in the insects he has examined (Fig. 162), while it is present in Melolontha, where the trachea is absent. LITERATURE ON THE WINGS Jurine, L. Nouvelle niethode de classer les Hyme'nopteres et les Dipteres. Geneve, 1807, 4°, pp. 319, 14 Pis. Observations sur les ailes des Hyrne'iiopteres. (Me"rn. acacl. Turin, 1820, xxiv, pp. 177-214.) Latreille, P. A. De la formation des ailes des Insectes. (Mem. sur divers sujets de 1'histoire naturelle des Insectes, etc. Paris, 1819. Fasc. 8.) De quelques appendices particulSers du thorax de divers Insectes. (Mem. du Mus. d'Hist. nat., 1821, vii, pp. 1-21, 354-363.) Chabrier, J. Essai sur le vol des insectes. (Me"m. du Mus. d'Hist. nat., 1820, vi, pp. 410-476; 1821, vii, pp. 297-372; 1822, viii, pp. 47-99, 349-403.) Separate, pp. 328, 13 Pis. Burmeister, Hermann. Handbuch der entornologie, i, 1832, pp. 96-106, 263- 267, 494-505. Untersuchungen liber die Fliigeltypen der Coleopteren. (Abhandl. d. naturf. Ges. Halle, 1854, ii, pp. 125-140, 1 Taf.) Romand, B. E. de. Tableau de 1'aile supe'rieure des Hyme'nopteres, 1 PI. Paris, 1839. (Revue Zool., ii, pp. 339; Bericht von Erichson fur 1839, pp. 54-56.) Lefebure, A. Communication verbale sur la pterologie des Lepidopteres. (Annal. Soc. Ent. France, 1842, i, pp. 5-35, 3 Pis. Also Revue Zool. Paris, 1842, pp. 52-58, 1 PI.) Deschamps, B. Recherches microscopiques sur 1'organisation des e'lytres des Cole'opteres. (Ann. sc. nat., sdr. 3, iii, 1845, pp. 354-363.) Heer, Oswald. Die Insektenfauna der Tertiargebilde von Oeningen und Radaboj., 1847, 1. Teil, pp. 75-94. Newman, E. Memorandum on the wing-rays of insects. (Trans. Ent. Soc. London, ser. 2, iii, 1855, pp. 225-231.) West wood, J. 0. Notes on the wing- veins of insects. (Trans. Ent. Soc. Lon- don, ser. 2, iv, 1857, pp. 60-64.) Loew, H. Die Schwinger der Dipteren. (Berlin, Entom. Zeitschr. , 1858, pp. 225-230.) Saussure, H. de. Etudes sur Paile des Orthopteres. (Ann. scienc. nat., 5 ser. x, p. 161.) Schiner, J. R. Ueber das Fliigelgeader der Dipteren. (Verhdl. k. k. Zool.-bot., Ges. \Vien, 1864, pp. 193-200, 1 Taf.) 148 TEXT-BOOK OF ENTOMOLOGY Hagen, H. A. Ueber rationelle Benennung des Geaders in den Fliigeln der Insekten. (Stettin. Ent. Zeitung, 1870, xxxi, pp. 316-320, 1 Taf.) Kurze Bemerkungen iiber das Fliigelgeader der Insekten. (Wiener Entom. Zeit., 1886, v, pp. 311, 312.) Plateau, F. Qu'est-ce que 1'aile d'un insecte ? (Stett. Ent. Zeit. Jahrg. 32, 1871, pp. 33-42, 1 Taf. Journal d. Zool., ii, 1873, pp. 126-137.) Moseley, H. N. On the circulation in the wing of Blatta orientalis and other insects, etc. (Quart. Journ. Micr. Sc. 1871, xi, pp. 389-395, 1 PI.) Roger, Otto. Das Fliigelgeader der Kafer. Erlangen, 1875, 90 p. Rade, E. Die westfalischen Donacien und ihre nachsten Verwandten. 3 Taf. (Vierter Jahresber. d. Westfal Prov.-Vereins f. Wiss. u. Kunst, 1876, pp. 52-87; Fliigel, pp. 61-68.) Katter, F. Ueber Inseckten-, speziell Schmetterlingsfltigel. (Entom. Nachr. , iv, 1878, pp. 279-281, 293-298, 304-309, 321-323.) Hofmann, Georg v. Ueber die morphologische Deutung der Insektenflugel. (Jahresber. d. akad.-naturwiss. Vereins, Graz. v Jahrg., 1879, pp. 63-68.) Kolbe, H. J. Das Fliigelgeader der Psociden und seine systematische Bedeut- ung. (Stettin. Entom. Zeitung, 1880, pp. 179-186, 1 Taf.) Die Zwischenraume zwischen den Punktstreifen der punktiertgestreiften Fltigeldecken der Coleoptera als rudimentare Kippen aufgefasst. (Jahresber. zool. Sektion d. Westfal. Prov.-Ver. f. Wiss. u. Kunst. Minister, 1886, pp. 57-59, 1 Taf.) Lee, A. Bolles. Les balanciers des Dipteres, leurs organes sensiferes et leurs histologie. (Recueil Zool. Suisse, i, 1885, pp. 363-392, 1 PI.) Poppius, Alfred. Ueber das Fliigelgeader der finnischen Dendrometriden. 1 Taf. (Berl. Entom. Zeitschr., 1888, pp. 17-28.) Comstock, J. H. On the houiologies of the wing-veins of insects. (American Naturalist, xxi, 1887, pp. 932-934.) Brauer, F. Ansichten iiber die palaozoischen Insekten und deren Deutung. (Annal. d. k. k. naturhist. Mus. Wien, Bd. i, 1886, pp. 86-126, 2 Taf.) Brauer, F., und J. Redtenbacher. Ein Beitrag zur Entwicklung des Fliigel- geaders der Insekten. (Zool. Anz. 1888, pp. 443-447.) Redtenbacher, J. Vergleichende Studien iiber das Fliigelgeader der Insekten. 12 Taf. (Annalen d. k. k. naturhist. Hofniuseums zu Wien, 1886, i, pp. 153-231.) Schoch, G. Miscellanea entomologica. I. Das Geader des Insektenfliigels ; II. Prolegomena zur Fauna dipterorum Helvetiae, Wissenschaftl. Beilage z. Programm d. Kantonsschule Zurich, 1889, 4°, 40 p.) Bondsdorff, A. von. Ueber die Ableitung der Skulpturverhaltnisse bei den Deck- fliigelii der Coleopteren. (Zool. Anz., 1890, xiii Jahrg., pp. 342-346.) Spuler, Arnold. Zur Phylogenie und Ontogenie des Fliigelgeaders der Schmet- terlinge. (Zeitschr. wissens. Zool., liii, 597-646, 2 Taf., 1892.) Also the writings of Adolph, Bugnion, Calvert, Comstock, Diez, Giraud, Gonin, Graber, Kellogg, Packard, Pratt, Scudder, Walsh. g. Mechanism of flight Marey's views on the flight of insects. — As we owe more to Marey than to any one else for what exact knowledge Ave have of the theory of flight of insects, the following account is condensed from his work entitled "Movement," The exceedingly complicated MECHANISM OF FLIGHT 149 movements of the wings would lead us, he says, to suppose that there exists in insects a very complex set of muscles of flight, but in reality, he claims, there are only the two elevator and depressor muscles of each wing.1 And Marey says that when we examine more closely the mechanical conditions of the flight of insects, we see that an upward and downward motion given by the muscles is sufficient to produce all these successive acts, so well co- ordinated with each other ; the resistance of the air effecting all the other movements. He also refers to the experiments of Giraud which prove that the insect needs for flight a rigid main-rib and a flexible membrane. If we take off the wing of an insect, and holding it by the small joint which connects it with the thorax, expose it to a current of air, •»»»*•>»,,,.«» .•>.*> ""^ "•>•«•»•% >Av-, •>«>>»•» •>'>.VS>VHJ"»<,»%^AS'.S.. ,-*•. vv vv, „>> ;.. •»^^^A^AA^A/^A^^^^AA^AAAAA<^AAA^AAAA/^A'Av^Vv^AAA^/^A,"^v^^ FIG. 163. —The two upper lines are produced by the contacts of a drone's wing- on a smoked cylinder. In the middle are recorded the vibrations of a tuning-fork (250 vibrations per second) for comparison with the frequency of the wing movements. Below are seen the movements of the wing of a bee. — After Marey. we see that the plane of the wing is inclined more and more as it is subjected to a more powerful impulse of the wind. The anterior nervure resists, but the membranous portion which is prolonged behind bends on account of its greater pliancy. The wings of insects may be regarded simply as vibrating wires, and hence the frequency of their movements can be calculated by the note produced. Their movements can be recorded directly on a revolving cylinder, previously blackened with smoke, the slightest touch of the tip of the wing removing the black and exposing the white paper beneath ; Pig. 163 was obtained in this way. By this method it was calculated that in the common fly the wings made 330 strokes per second, the bee 190, the Macroglossus 72, the dragon-fly 1 Von Lendenfeld, however, points out the fact that Straus-Durckheim proved that the wings of beetles are moved by a complicated system of numerous muscles. " In the Lepidoptera I have never found less than six muscles to each wing, as also in the Hymenoptera and Diptera." " The motions of the wings of Libellulidaj are the combined working of numerous muscles and cords, and of a great number of chitinous pieces connected by joints." 150 TEXT-BOOK OF ENTOMOLOGY 28, and the butterfly (Pier is rapes) 9. Tims the smaller the species, the more rapid are the movements of the wings. The path or trajectory made by the tip of the wing is like a figure 8. Marey obtained this by fastening a spangle of gold-leaf to the extremity of a wasp's wing. The insect was then seized with a pair of for- ceps and held in the sun in front of a dark back- ground, the luminous tra- jectory shaping itself in the form of a lemniscate (Fig. 164). FIG. 164. — Appearance of a wasp flying in the sun the extremity of the wing- is gilded. — After Marey. To determine with accuracy the direction taken by the wing at different stages of the trajectory, a small piece of capillary glass tubing was blackened in the smoke of a candle, so that the slightest touch on the glass was sufficient to remove the black coating and show the direction of movement in each limb of the lemniscate. This experiment was arranged as shown in Fig. 165. Different points on the path of movement were tested by the smoked rod, and from the track along which the black had been removed the direction of movement was deduced. This direction is represented in the figure by means of arrows. Theory of insect flight " The theory of insect flight," says Marey, " may be completely explained from the preceding experiments. The wing, in its to-and-fro move- ment, is bent in various directions by the resistance of the air. Its action is always that of an inclined plane striking against a fluid and utilizing that part of the resistance which is favorable to its onward progression. FIG. 165. — Experiment to test the direction of move- " illlS mechanism IS the mentof an insect's wing: a, a', b, b', different positions of the smoked rod. same as that of a water- man's scull, which as it moves backwards and forwards is obliquely inclined in opposite directions, each time communicating an impulse to the boat." The mechanism in the case of the insect's wing is far simpler, THEORY OF INSECT FLIGHT 151 I W o- o however, than in the process of sculling, since " the flexible mem- brane which constitutes the anterior part of the wing presents a rigid border, which enables the wing to incline itself at the most favorable angle." " The muscles only maintain the to-and-fro movement, the resist- ance of the air does the rest, namely, effects those changes in surface obliquity which determine the formation of an 8-shaped tra- jectory by the extremity of the wing." Lendenfeld has applied photography to determine the position of the wings of a dragon-fly, and Marey has carried chronophotography farther to indicate the normal trajectory of the wing, and to show the position in flight. Fig. 166 shows a bee in various phases of flight. " The insect sometimes assumes almost a horizontal position, in which case the lower part of its body is much nearer the object-glass than is its head, and yet both extremities are equally well denned in the photograph. The successive images are separated by an interval of ^ of a second (a long time when compared to the total time occu- pied by a complete wing movement, i.e. T^ of a second). And hence it is useless to attempt to gain a knowl- edge of the successive phases of move- ment by examining the successive photographs of a consecutive series rep- resenting an insect in flight. Never- theless an examination of isolated images affords information of extreme interest with regard to the mechanism of flight. "We have seen that owing to the resistance of the air the expanse of wing is distorted in various directions by atmospheric resistance. Now, as the oscillations during flight are executed in a horizontal plane, the obliquity of the wing-surface ought to diminish the apparent breadth of the wing. This appearance can be seen in Fig. 167. There is here a comparison between two Tipulae : the one in the act of flight, the other perfectly motionless and resting against the glass window. "The motionless insect maintains its wings in a position of vertical exten- r_ a> »-j O 152 TEXT-BOOK OF ENTOMOLOGY sion ; the plane is therefore at right angles to the axis of the object-glass. The breadth of the wing can be seen in its entirety ; the nervures can be counted, and the rounding off of the extremities of the wings is perfectly obvious. On the other hand, the flying insect moves its wings in a horizontal direction, and owing to the resistance of the air the expanse of the wings is obliquely disposed, and only the projection of its surface can be seen in the photograph. This is why the extremity of the wings appears as if it were pointed, while the other parts look much narrower than normal. The extent of the obliquity can be measured from the apparent alteration in width, for the projection of this plane with the vertical is the sine of the angle. From this it may be gathered that the right wing (Fig. 108, third image) was inclined at an angle of about 50° with the vertical, say 40° with the horizontal. This inclination necessarily varies at different points of the trajectory and must augment with the rapidity MECHANISM OF THE WINGS 153 of movement ; the obliquity reaching its maximum in those portions of the wings which move with the greatest velocity, namely, towards the extremities. The result is that the wing becomes twisted at certain periods of the move- ment." (See the fourth image in Fig. 168.) The position of the balancers seems to vary according to that of the wings. (Marey's Movement, pp. 253-257.) Graber's views as to the mech- anism of the wings, flight, etc. — Although in reality insects pos- sess but four wings, nature, says Graber, evidently endeavors to make them dipteral. This end is attained in a twofold manner. In the butterflies, bees, and cicadas, the four wings never act independently of each other, as two individual pairs, but they are always joined to a single flying plate by means of peculiar hooks, rows of claws, grooved clamps, and similar contrivances proceeding from the modified edges of the wings ; indeed, this connection is usually carried so far that the hind wings are entirely taken in tow by the front, and consequently possess a relatively weak mechanism of motion. The other mode of wing reduction consists in the fact that one pair is thrown entirely out of employment. We observe this for instance in bugs, beetles, grasshoppers, etc. In the meantime, then, we may not trust to appearances. As their devel- opment indeed teaches us, the wings as well as the additional members must be regarded as actual evagina- tions of the common sockets of the body, and in order especially to refute the prevalent opinion that these wing-membranes are void of sensation, it should be remembered that Leydig has proved the existence, as well as one can be con- vinced by experiment, of a nerve-end apparatus in certain basal or radical veins 154 TEXT-BOOK OF ENTOMOLOGY of the wing-membrane, which is very extensive and complicated, and therefore indicates the performance of an important function, perhaps of a kind of balancing sense, and also that these same insect wings, with their delicate membrane, are very easily affected by different outside agents, as, for instance, warmth, currents of air, etc. Usually in their inactive or passive state the wings are held off horizontally from the body during flight, and are laid upon the back again when the insect alights ; but an exception occurs in most butterflies and Neuroptera, among which the wing-joint allows only one movement round the oblique and long axis of the wings. From FIG. 169. — Anterior part of a Cicada for demonstrating the mechanism of the articulation of the fore wing : a, articular head ; ?<, articular pan, frog, or cotyla ; ff, elastic band ; c, cl, (, system of elastic rods ; t\, /'3, 1st and 2d abdominal segments. Iff, hind wings. — After Graber. this cause, too, the insects just mentioned can unfold their wings suddenly. The transition of the wings from the active to the resting condi- tion seems to be by way of a purely passive process, which, there- fore, usually gives no trouble to the insect. The wing being extended by the tractive power of the muscles, flies back, when this ceases, to its former or resting posture by means of its natural elas- ticity, like a spiral spring disturbed from its balance. The structure of this spring joint is very different, however. It usually consists (Fig. 109) of two parts. The wing can move itself up and down in a vertical plane by means of the forward joint, and at the same time can rotate somewhat round its long axis, because the chitinous part mentioned above is ground off after the fashion of a mandrel. The hinder joint, at a greater distance from the body, virtually consists of a rounded piece (a) capitate towards the outside, and of a prettily hollowed socket (6) formed by the union of the thick ribs of the hind wings, which slides round HOW THE WINGS ARE FOLDED 155 the head joint when the wings snap back upon the back. The mechanism which causes this turning is, however, of a somewhat complicated nature. The most instrumental part of it is the powerful elastic band (-) ; /, edge of the right wing, passing into' the tion Of the two most prev- corresponding groove (fit) of the left; Di, diaphragm for the attachment of the tergal muscle of the uietasternum ; Di\ (not alent methods which the explained by author); A'er, acetabulum of the coxa (////); ,sV>, cabinet-maker uses in join- chitinous process for the attachment of the coxal muscle ; -Fe, femur; Soh, tibia; £„, sternum. — After Gruber. ing boards together. The act of folding the broad hind wings among beetles is not less significant than the arrangement of the fore wing. If we forcibly spread out the former in a beetle which has just been killed and then leave it to its own resources again, we observe the following result : According to its peculiar mode of joining, the costal vein on the fore edge approaches the mid or discoidal vein of the basal half as well as the distal half of the wing, whence arises a longitudinal fold which curves in underneath. Then the distal half snaps under like the blade of a pocket knife and lies on the plane of the costal edge of the wing, while it also draws after it the neighboring wing-area. The soft hinder-edge portion turns in simultaneously when this wing-area remains fixed to the body while the costal portion is moving towards the middle line of the body. The wing-membrane of almost all insects have, moreover, the capability of folding themselves somewhat, and this power of extending or contracting the wing-membrane at will is of great importance in flight. Yes, but how is the folded wing spread out again ? The fact may be shown more simply and easily than one might suppose, and may be most plainly demonstrated even to a larger public by making an artificial wing exactly after the pattern of the natural one, in which bits of whalebone may take the place 156 TEXT-BOOK OF ENTOMOLOGY of veins and a piece of india rubber the membrane spread out between them. The reader will be patient while we just explain to him the act of unfolding of the membranous wing of the beetle. The actual impulse for this unfolding is due to the flexor muscles which pull on, and at the same time somewhat raise . „ the vein on the costal edge. By this means the mem- branous fold lying directly behind the costal vein is first spread out. But since this fold is connected with the longitudinal fold of the distal end of the wing which closes like a blade, the wing-area last mentioned which is attached to the middle fold of the wing by the elastic spring-like diag- onal vein becomes stretched out. The hinder rayed por- tion adjacent to the body is, on the other hand, simply drawn along when the wing stands off from the body. In order to properly grasp the mechanism of the insect wing we must again examine its mode of articulation to the body somewhat more accurately. If we select the halteres of a garden gnat (Tipula) at the moment of exten- sion, we shall find them to be formed almost exactly after the pattern of our oars, since the oblong oar- blade passes into a longitu- dinal handle. The pedicel of the balancer is formed by the thick longitudinal primary veins of the wing- membrane. This pedicel (Fig. 171) is implanted in the side of the thorax in such a manner that the wing may be compared to the top of a ninepin. One may think, and on the whole it is actually the fact, that the stiff pedicel of the wing is inserted in the thoracic wall, and that a short portion of it (Fig. 172), projects into the cavity of the thorax. It is true there is no actual hole to be found in the thoracic wall, as the intermediate MECHANISM OF THE WING 157 space between the base or pedicel of the wing and the aperture in the thorax is lined with a thin yielding membrane, on which the wing is suspended as on an axle-tree. According to this, therefore, the insect wing, as well as any other appendage of arthropods, acts as a lever with two arms. The reader can then conjecture what may be the further mechanism of the wing machine. We only need, now two muscles dia- metrically opposed to each other and seizing on the power arm of the wing, one of which pulls down the short wing arm, thereby rais- ing the oar, while the other pulls up the power arm. And indeed the raising of Fin. 172. —Scheme of the flying apparatus of an insect: mnl, thoracic walls ; ab, wings ; c, pivot ; d, point of insertion of the depressor muscle of the wing (ted); — a, that of the ele- vator of the wing (ai) ; »•«, muscle for expanding, — ml, for contracting, the walls of the thorax. — After Graber. the wing follows in the man- ner indicated, since a muscle (hi) is attached to the end of the wing-handle (a) which projects freely into the breast cavity by the contraction of which the power arm is drawn down. On the other hand, we have been entirely mistaken in reference to the mechanism which lowers the wings. The muscle concerned, that is M, is not at all the antagonist s ch- ef the elevator muscle of the wing, since it is placed close by this latter, but nearer to the thoracic wall. But then, how does it come to be the counterpart of its neighbor ? In fact, the lever of the wing is situated in the projecting piece alone. The extensor muscle of the wing does not pull on the power arm, but on the resistant arm on the other side of the fulcrum (c). The illustration shows, however, how such a case is possible. The membrane of the joint fastening the wing-stalk to the thorax is turned up outwards below the stalk like a pouch. The tendon of the flexor of the wing passes through this pouch to its point of attachment (c) lying on the other side of the fulcrum (d). Thus it is very simply explained how two muscles which act in the same direction can never- theless have an entirely contrary working power. This is in a way the bare physical scheme of the flying machine by the help of which we shall more easily become acquainted with its further details. Dragon-flies are unquestionably the most suitable FIG. 173 —Muscles of the objects for the study of the muscles pulling directly fore wing of a dragon-fly (an, J * ax), exposed by removing the on the wing itself. If the lateral thoracic wall (Fig. thoracic walls: At, //„ eleva- jys) be removed or the thorax opened lengthwise tors, — SI-SB, depressors, of the wings (*„ *2, rotators). — After there appears a whole storehouse of muscular cords Graber- which are spread out in an oblique direction between the base of the wing and the side of the thoracic plate. There is first to be ascertained, by the experiment of pulling the individual muscles in the line with a pincers, which ones serve for the lifting and which for the lowering 158 TEXT-BOOK OF ENTOMOLOGY of the wings. In dragon-flies the muscles are arranged in two rows and in such a way that the flexors or depressors (s, 1 bis) cling directly to the thoracic wall (compare also the muscle dk in Fig. 172 and se in Fig. 174), while the raiser or extensor (hi, to h 2, Fig. 172, hi and Fig. 174 he) lie farther in. The form of the wing-muscles is sometimes cylindrical, sometimes like a prism, or even ribbon-like. However, the contracted bundles of fibres do not come directly upon the joint-process we have described, but pass over often indeed at a very considerable distance from them, into peculiar chitinous ten- dons. These have the form of a cap-like plate, often serrate on the edge, which is prolonged into a thread, which should be considered as the direct continua- tion of the base of the wings. The wings, therefore, sink down into the tho- bg gi tihm FIG. 174. — Transverse section through the thorax of a locust (Stenobothrus) : < leg; A, heart: ga, ventral cord; se, depressor, — he, elevator, of the wing (.7?) ; b-r, lateral muscles which expand the thoracic walls; — 1m, longitu- dinal muscles which contract them; xtim. ///////, muscles to the legs; bg, apodeines. —After Graber. FIG. 1T5. — Inner view of a portion of the left side of body of Libellula depressa, showing a part of the mechanism of flight, viz., some of the chitinous ridges at base of the upper wing, and some of the insertions of the tendons of muscles : A, line of section through the base of the upper wing, the wing being supposed to be directed backwards. C, upper portion of mech- anism of the lower wing; b, lever extending between the pieces connected with the two wings. — After von Lendenfeld, from Sharp. racic cavity as if they were a row of cords ending in handles where the strain of the muscles is applied. As may be seen in Fig. 173, the contractile section of several of the muscles of the wing (s5) is extraordinarily reduced, while its thread-like tendon is pro- portionately longer. This gradation being almost like that of the pipes of an organ in the length of the wing-muscles, as may so easily be observed in the large dragon-flies, plainly indicates that the strain of the individual muscles is quite different in strength, since, as the phenomenon of flight demands it, the different parts of the base of the wing become respectively relaxed in very dissimilar measure. We have thus far discussed only the elevator and depressor muscles. Other groups (sas3) are yet to be added, however, crossing under the first at acute THE MUSCLES OF THE WINGS 159 angles, which when pulling the wing sidewise, bring about in union with the other muscles a screw-like turning of the wings. While in dragon-flies all the muscles which are principally influential in mov- ing the wing are directly attached to it, and thus evidently assert their strength most advantageously, the case is essentially different with all other insects. Here, as has already been superficially mentioned above, the entire set of muscles affecting the wing is analyzed into two parts of which the smaller only is usually directly joined to the wings, while the movement is indirectly influenced by the remainder (Graber). In the dragon-fly the two wings are "brought into correlative action by means of a lever of unusual length existing amongst the chitinous pieces in the body wall at the base of the wings (Fig. 175, 6). The wing-muscles are large; according to von Lendenfeld there are three elevator, five depressor, and one abductor muscles to each wing. He describes the wing-movements as the results of the correlative action of numerous muscles and ligaments, and of a great number of chitinous pieces connected in a jointed manner" (Sharp). If again we take the longitudinal section of the thoracic cavity of gnats in Fig. 171, we shall perceive a compactly closed system of muscular bars intersecting each other almost at right angles and interlaced with a tangled mass of tracheae, some of which muscles extend (Im) longitudinally, that is from the front to the back, while others (6-r) stretch out in a vertical direction, that is between the plates of the abdomen and back. In order that we may more easily comprehend this important muscular apparatus we will illustrate the thoracic cavity of insects by an elastic steel ring (Fig. 172), to which we may affix artificial wings. If this ring be pressed together from above downward, along the line rs, thus imitating the pulling of the vertical or lateral thoracic muscles, then the wings on both sides spring up. This is to be explained by the fact that through this manipulation a press- ure is exerted on the lifting power arm of the wings. If, on the other hand, the ring be compressed on the sides OH/), which is the same thing as if the longi- tudinal muscles contracted the thorax from before backward, and thus arched it •more, then the wings are lowered. Agrionime, according to Kolbe, can fly with the fore pair of wings or with, the hind pair almost as well as with both pairs together. Also the wings of these insects can be cut off before the middle of their length without injuring their power of flight. Butterflies, Catocalae, and Bombycidte fly after the removal of the hind wings. Also the balancers of the Diptera must be useful in flying, since their removal lessens the power of flight. Chabrier regarded the under sides of the shell-like extended wing-covers of the beetles as wind-catchers, which, seized by wind currents, carry the insect through the air. We may also consider the wing-covers as regulators of the centre of gravity of flight. The observations of insects made by Poujade (Ann. Soc. Ent., France, 1887, p. 197) during flight teaches us, says Kolbe, that in respect to the movement during flight of both pairs of wings, they may be divided into two categories : - 1. Into those where both pairs of wings (together), either united, and also when separated from each other, perform flight. Such are the Libellulidse, Perlidae, Sialidfe, Hemerobidse, Mymeleonidse, AcridiidaB, Locustidae, Blattidse, Termitidse, etc. 2. Into those whose fore and hind wings act together like one wing, since they are connected by hooks (hamuli), as in certain Hymenoptera, or are at- tached in other ways. Here belong Hymenoptera, Lepidoptera, Trichoptera, Cicadidee, Psocidte, etc. 160 TEXT-BOOK OF ENTOMOLOGY The musculature of the mesothorax and metathorax is similar in those in- sects both of whose pairs of wings are like each other, and act independently during flight, viz. in the Libellulidae. On the other hand, in the second cate- gory, where the fore and hind wings act as a single pair and the fore wings are mostly larger than the hinder (except in most of the Trichoptera), the muscula- ture of the mesothorax is more developed than that of the metathorax. To neither category belong the beetles, whose wing-covers are peculiar organs of flight, and not for direct use, and the Diptera, which possess but a single pair of wings. In the beetles the hind wings, in the Diptera the fore wings, serve especially as organs of flight. It may be observed that the Diptera are the best fliers, and that those insects which use both pairs of wings as a single pair fly better than those insects whose two pairs of wings work independently of each other. An exception are the swift-flying Libellulidae, whose specially formed muscles of flight explain their unusual capabilities for flying (Kolbe). LITERATURE ON FLIGHT Marey, E. J. La machine animale. Locomotion terrestre et aerienne. Paris, 1874. " Me"moire sur le vol des insectes et des oiseaux. (Annal. Scienc. natur., 5 ser., Zool. xii, 1869, pp. 49-150 ; 5 ser., Zool. xv, 1872, 42 Figs.) — Note sur le vol des insectes. (Compt. rend, et Mem. Soc. d. Biol. Paris, 4 ser., v, 1869, C. R. pp. 136-139.) Recherches sur le mecanisme du vol des insectes. (Journal de 1'Anatomie et de la Physiologic, 6 Annee, 1869, pp. 19-36, 337-348.) — Animal mechanism. New York, 1879, pp. 180-209. Movement. New York, 1895, pp. 239-274. Hartings. Ueber den Flug. (Nieclerland. Archiv f. Zoologie, iv, Leiden, 1877-78.) Lucy. Le vol des oiseaux, chauvesouris et insectes. Paris. Tatin, V. Experiences physiologiques et synthe'tiques sur le mecanisme du vol. (Ecole prat. d. haut. e"tud. Physiol. experim. Trav. du laborat. de> Marey, 1877, pp. 293-302.) Experiences sur le vol mecanique. (Ibid., 1876, pp. 87-108.) Bellesme, Jousset de. Recherches experimentales sur les f onctions du balancier chez les insectes Dipteres, Paris, 1878, 96 pp., Figs. — Sur une fonction de direction dans le vol des insectes. (Compt. rend., Ixxxix, 1879, pp. 980-983.) Pettigrew, J. Bell. On the mechanical appliances by which flight is attained in the animal kingdom. (Trans. Linn. Soc., 1868, xxvi, Pt. I, pp. 197-277, 4 PI.) On the physiology of wings. (Trans. Roy. Soc. Edinburgh, 1871, xxvi, pp. 321-446.) Krarup-hansen, C. J. L. Beitrag zu einer Theorie des Fluges der Vogel, Insekten und Flrdermause. (Copenhagen u. Leipzig, Fritsch, 1869, 48 pp.) Lendenfeld, R. V. Der Flug der Libellen. (Sitzungsber. d. kais. Akad. d. Wiss. Wien, Ixxxiii, 1881, pp. 289-376, 7 Taf. ; Zool. Anz., 1880, pp. 82.) Girard, M. Note sur diverses experiences relatives a la fonction des ailes chez les insectes. (Ann. Soc. Ent. France, 4 ser., ii, 1862, pp. 154-162.) Muhlhauser, F. A. Ueber das Fliegen der Insekten. (22. bis 24., Jahresb. d. Pollichia, Durkheim, 1866, pp. 37-42.) Plateau, F61ix. Recherches experimentales sur la position du centre de gravit^ chez les insectes. (Archiv d. Scienc. phys. et natur. d. Geneve, Nouv. pe>iode, xliii, 1872, pp. 5-37.) LITERATURE ON THE FLIGHT OF INSECTS 101 Plateau, Felix. Ueber die Lage des Schwerpunktes bei den Insekten. Auszug. (Naturforscher v. Sklarek, v. Jahrg., 1872, pp. 112-113.) Recherches physico-chimiques sur les articules aquatiques. (Bull. d. 1'Acad. Roy. Belg., xxxiv, 1872, pp. 1-50, Fig.) Qu'est-ce que 1'aile d'un insecte? (Stett. Ent. Zeit., 1871, pp. 33-42, PI.) L'aile des insectes. (Journ. d. Zool., ii, 1873, pp. 126-137.) Perez, J. Sur les causes de bourdonnement chez les insectes. (Comptes rend., Ixxxvii, p. 535, Paris, 1878.) Strasser, Hans. Mechanik des Fluges. (Archiv f. Anat. u. Phys., 1878, p. 319-350, 1 Taf.) Ueber die Grundbedingungen der aktiven Locomotion. (Abhandl. d. naturf. Gesellsch., Halle, 1880, xv, pp. 121-196, Figs.) Moleyre, L. Recherches sur les organes du vol chez les insectes de 1'ordre des Hemipteres. (Compt. rend, de 1'Acad. d. Scienc. de Paris, 1882, xcv, pp. 349-352.) Amans, P. Essai sur le vol des insectes. (Revue d. Sc. Nat. Montpellier, 3 ser., ii, 1883, pp. 469-490, 2 PI. ; iii, 1884, pp. 121-139, 3 PI.) Etude de 1'organe du vol chez les Hyme'nopteres. (Ibid., iii, pp. 485-522, 2 PI.) Comparaisons des organes du vol dans la se"rie animale. Des organes du vol chez les insectes. (Annal. d. Scienc. nat. Zool., 6 se"r., xix, pp. 1-222, 8 PL) Mullenhoff, K. Die Grosse der Flugflachen. (Pfliiger's Archiv f. d. ges. Physiologic, 1884, xxxv, pp. 407-453.) Die Ortsbewegungen der Tiere. (Wissensch. Beil. z. Programm d. Andreas-Realgymnas. Berlin, 1885, 19 pp.) Poujade, G. A. Note sur les attitudes des insectes pendant le vol. (Ann. Soc. Ent. France, 1884, 6 se>., iv, pp. 197-200, 1 PI.) Krancher, 0- Die Tone der Flugelschwingungen unserer Honigbiene. (Deut- scher Bienenfreund, 1882, 18. Jahrg., pp. 197-204.) Landois, H. Ueber das Flugvermogen der Insekten. (Natur. und Offenbarung, vi, 1860, pp. 529-540.) Ungern-Sternberg, von. Betrachtungen iiber die Gesetze des Fluges. (Zeitschr. d. Drutschen Vereins z. Forderung d. Luftschiffahrt-Naturwissensch. Wochenschrift v. Potonie, iv, 1889, p. 158.) Baudelot, E. Du raecanisme suivant lequel s'effectue chez les Cole"opteres le retract des ailes infe'rieures sous les elytres au moment du passage a l'e"tat de repos. (Bull. Soc. d. Scienc. nat., Strasbourg, 1 Anne"e, 1868, pp. 137- 138.) Ris, Fr. Die schweizerischen Libellen. Schaffhausen, 1885. (Beiheft der Mitteil. d. Schweiz. Ent. Ges., vii, pp. 35-84.) M 162 TEXT-BOOK OF ENTOMOLOGY Fin. 17i>. — Abdomen of Termesfiavipes : 1-10, the ten tergites ; 1-9, the nine urites ; o, cercopod. THE ABDOMEN AND ITS APPENDAGES In the abdomen the segments are more equally developed than elsewhere, retaining the simple annular shape of embryonic life, and from their generalized nature their number can be readily distinguished (Fig. 176). The tergal and sternal pieces of each segment are of nearly the same size, the tergal often over- lapping the sternal (though in the Coleoptera the sternites are larger than the tergites), while there are no pleura! pieces, the lateral region being membranous when visible and bearing the stigmata (Fig. 177, L). In the terminal segments beyond the genital outlet, however, there is a reduction in and loss of segments, espe- cially in the adults of the metabolous orders, notably the Panorpidse (Fig. 177), Diptera, and aculeate Hymenoptera; in the Chrysididae only three or four being usually visible, the distal segments being reduced and telescoped inward. The typical number of abdominal segments (uromeres), i.e. that occurring in each order of insects, is ten ; and in certain families of Orthoptera, eleven. In the embryos, however, of the most general- i" c Fin. 177. — End of abdomen of Panorpn ih'hilix drawn out. the chitinous pirn's shaded : /,, lateral, 1>, dorsal view ; <•. jointed eeivopoda. — (Ussier del. ized winged orders, Orthoptera (Fig. 199), Dermaptera, and Odonata, eleven can be seen, while Heymons has recently detected twelve in blattid and Forficula embryos, and he claims that in the nymphs of certain Odonata there are twelve segments, the twelfth being THE MEDIAN SEGMENT 163 represented by the anal or lateral plates. It thus appears that even in the embryo condition of the more generalized winged insects, the number of uromeres is slightly variable. We have designated the abdomen as the urosome ; the abdominal segments of insects and other Arthropods as uromeres. and the sternal sclerites as uro- vti'rnites, farther condensed into urites. (See Third Report U. S. Entomological Commission, 1883, pp. 307, 324, 4:)o, etc.) The reduction takes place at the end of the abdomen, and is usually correlated with the presence or absence of the ovipositor. In the more generalized insects, as the cockroaches, the tenth seg- ment is, in the female, com- pletely aborted, the ventral plate being atrophied, while the dorsal plate is fused dur- ing embryonic life, as Cholod- kovsky has shown, with the ninth tergite, thus forming the suranal plate. In the advanced nymph of Psylla the hinder segments of the abdomen appear to be fused together, the traces of segmenta- tion being obliterated, though the segments are free in the first stage and in the imago (Fig. 178). It thus recalls the abdomen of spiders, of Limulus, and the pygi- dium of trilobites. FIG. 178. — Nymph of the pear tree Psylla, with its glandular hairs. — After Slingerland. Bull. Div. Ent. U. S. Dep. Agr. The median segment. — There has been in the past much discussion as to the nature of the first abdominal segment, which, in those Hymenoptera exclusive of the phytophagous families, forms a part of the thorax, so that the latter in reality consists of four segments, what appearing to be the first abdominal segment being in reality the second. Latreille and also Audouin considered it as the basal segment of the abdo- men, the former calling it the "segment m6diaire," while Newman termed it the " propodeum." This view was afterward held by Newport, Schiodte, Rein- hard, and by the writer, as well as Osten Sacken, Brauer, and others. The first author to attempt to prove this by a study of the transformations was New- port in 1839 (article "Insecta"). He states that while the body of the larva is in general composed of thirteen distinct segments, counting the head as the first, "the second, third, fourth, and, as we shall hereafter see, in part also the fifth, together form the thorax of the future imago" (p. 870). Although at first inclined to Audouiii's opinion, he does not appear to fully accept it, yet farther 164 TEXT-BOOK OF ENTOMOLOGY on (p. 921) he concludes that in the Hymenoptera the "fifth" segment (first ab- dominal) is not in reality a part of the true thorax, " but is sometimes connected more or less with that region, or with the abdomen, being intermediate between the two. Hence we have ventured to designate it the thoracico-abdumiiial seg- ment." Had he considered the higher Hymenoptera alone, he would undoubtedly have adopted Latreille's view, but he saw that in the saw-flies and Lepidoptera the first abdominal segment is not entirely united with the thorax, being still connected with the abdomen as well as the thorax. Keinhard in 1865 reaffirmed Latreille's view. In 1866 we stated from observa- tions on the larvse made three years earlier, tliat during the semipupa stage of Bomb us the entire first abdominal segment is "transferred from the abdomen to the thorax with which it is intimately united in the Hymenoptera," and we added that we deemed this to be " the most essential zoo- logical character separating the Hymenoptera from all other insects." (See Fig. 93, showing the gradual transfer and fusion of this segment with the thorax.) In the saw-flies the fusion is incom- plete, as also in the Lepidoptera, while in the Diptera and all other orders the thorax consists of but three segments. (See also pp. 90-92.) The cercopoda. — We have applied this name to the pair of anal cerci appended to the tenth abdominal segment, and which are generally regarded as true abdominal legs. As is now well known, the embryos of insects of different orders have numerous temporary pairs of abdominal appendages which arise in the same manner, have the same embryonic structure, and are placed in a position homologous with those of the thorax. In the embryo of (Ecanthus rudi- mentary legs appear, as shown by Ayers, on the first to tenth abdominal segment, FIG. 179. — Abdomen of jfa- the last or tenth pair becoming the cerco- ruin* maritima. 9, seen from .... -. beneath: the left half of the sth poda ; and similar rudimentary appendages plate removed: I-IX , •• -i j i • j i p ai segments ;c,cercopoda have been detected in the embryos ot C'i, coxnl iflands ; fix. eoxal stvlets /~i i T • i j TT ir, ovipositor.— After oude.muis Coleoptera, Lepidoptera, and Hymenoptera from (Apidae). Cholodkowsky has observed eleven pairs of abdominal appendages in Phyllodromia. They are very long and multiarticulate in the Thysanura (Fig. 17'J). In the Dermaptera they are not jointed and are forcep-like. It should also be observed that in the larva or Sisyra (Fig. 181) there are seven pairs of 5-jointed abdominal appendages, though these may be secondary structures or tracheal gills. In the Per- THE CERCOPODA 165 lidse and the Plectoptera (Ephemeridse), they are very long, some- times over twice as long as the body, and composed of upward of 55 joints ; they also occur in the Pan- orpidjB (Fig. 177). In the dragon-flies the cerci are large, but not articulated, and serve as claspers or are leaf -like1 (Fig. 180). In a few Coleoptera, as the palm-weevil (Rhynchophorus phoenicis), Cerambyx, Drilus, etc., the so-called ovi- positor ends in a hairy, 1 -jointed, palpi- form cercus. Short 25-jointed cercopoda are present in Termi- tidae, and 2- jointed ones in Embiidse. The anal cerci are present in the Orthop- tera and, 1 •,,. Wiieil multl- articulate, function as abdominal antennae. They are longest in the Mantidse (Fig. 182); they also occur in the larva of the saw- fly, Lyda (Fig. 183). Dr. A. Dohrn has stated that the cerci of Gryllotalpa are true sensory organs, and we have called those of the cock- roach abdominal antennae, having detected about ninety sacs on the upper side of each joint of the stylets, which are , supposed to be olfactory in nature, and FIG. ISO. — End of abdomen of J B FIG. 181. — Larva of Sisyra, from beneath. £, an abdominal appendage. Westwood, from Sharp. -or FIG. 182. — Cercojioda (v) of Mantis. — After Lacaze-l)u- thiers. keros, 9 ; «>•. urosternite ; which are larger and more numerous (n\ outer, i>: inner styles of the ovi- . positor; ii, nth abdominal segment; than similar sacs or pits in the antennae c, cercopod. 1 Heymons, however, denies that the so-called cerci in Odonata are such, and claims that they are the homologues of the "caudal processes" (superior terminal appendages of Calvert), because they arise from the tenth abdominal segment. 166 TEXT-BOOK OF ENTOMOLOGY of the same insect.1 From his experiments upon decapitated cock- roaches, Graber concluded that these cerci were organs of sniell. FIG. 1S3. — Lyda larva: a, head; b, end of body seen from above ; c, from side, with cercopod. Haase regarded these appendages, from their late development and frequent reduc- tion, as old inherited appendages which are approaching atrophy through disuse. Cholodkowsky states that Tridactylus, a form allied to Gryllotalpa, bears on the tenth abdominal segment tsvo pairs of cerci (ven- tral and dursal), and that the ventral pair may correspond to the atrophied appendages of the tenth embryonic segment of Phyllo- dromia, with which afterward the eleventh segment becomes fused. The eercopods are not necessarily confined to the eleventh or to the tenth segment, for when there are only nine segments, with the vestige Xipliidium, they arise from the ninth uromere, and in the roaches, as Panesthia, in which there are but seven entire appended to the last or eighth uromere. of a tenth, as in more modern cock- segments, they are 1 Amer. Nat., iv, December, 1870. THE OVIPOSITOR 167 As to the homology and continuity of these cercopods with the ventral outgrowths of the embryo, several embryologists, notably Wheeler, are emphatic in regarding them as such. It thus appears that either the embryonic appendages of the seventh or eighth, ninth or tenth uromere may persist, and form the cercopoda of the adult. The ovipositor. — The end of the oviduct is guarded by three pairs of dhitinous, unjointed styles closely fitted together, forming a strong, powerful apparatus for boring into the ground or into leaves, stems of plants, the bodies of insects, or even into solid wood, so that the eggs may be deposited in a place of safety. In the ants, wasps, and bees the ovipositor also functions as a sting, which is further provided with a poison-sac. Morphologically, the ovipositor is composed of three pairs of un- jointed styles (rhabdites of Lacaze-Duthiers, gonapopliyses of Huxley), which are closely oppressed to or sheathed within each other, the eggs passing out from the end of the oviduct, which lies, as Dewitz states, between the two styles of the lowest or innermost pair, and under the cross-bars or at the base of the stylets mentioned; the styles or blades spreading apart to allow of the passage of the egg. The ovipositor is best developed in the Thysanura (Fig. 179, Cam- podea excepted), in Orthoptera (Fig. 184), in the Odonata, Hemiptera, certain P h y s a p o d a, Rhaphiidse, and in the phytophagous Hymen- optera, where it is curi- ously modified to form a rather complicated saw for cutting slits in wood or leaves (Fig. 185). It is wanting or quite imperfect in Coleoptera, Diptera, and Lepidoptera. Morphologically, the ovipositor appears to be formed out of the abdominal appendages of the seventh, eighth, and ninth segments of the female, which, instead of disappearing in the orders first men- tioned, persist as permanent styles. Wheeler asserts from his study of the embryonic development of Xiphidium " there can be no doubt concerning the direct continuity of the embryonic appendages with the gonapophyses." He goes on to say : — FIG. 185. — Saw of Ilylotoma : of tho ovipositor of the honoy-hee attached to trachea-; t'uroiit stages : //, 1st ; I/", M or middle ; and c , 'M pair of papilla-. — After Dewitz. the valves (stachelscheiden). The two buds of the ninth segment give rise to the vagina and to the oviducts, and these unite second- arily with the posterior end of the ovaries. The genital appendages MORPHOLOGY OF THE OVIPOSITOR 171 of the male correspond to those of the female, and arise from four imaginal buds situated on the under side of the tenth abdominal segment. In the ants, according to Dewitz, the genital armature is derived from imaginal buds situated on the under side of the seventh, eighth, and ninth abdominal segments. Bugnion has observed the forma- tion of six imaginal buds of the genital armature in the larva of a chalcid (Encyrtus, Figs. 41, 42, 191, qlq~, poison reservoir; I), accessory gland ; sheathing style or sting-" feeler "; Sf>\ sting; £a, sheath; Q, quadrate plate ; O, oblong piece; II', angular piece; £, base of the sting and stylets ; .s7//', ,s'M", the two barbed stylet? or darts. 2, sting seen from the ventral face ; lettering as in the other figure. — After Kraepelin, from I'errier. cal history of these styles. Those authors who have examined the elements of the ovipositor, and regard them as homologues (homodynamous} of the limbs, are Weismann (1866), Ganin (1869), Packard (1871), Ouljanin (1872), Kraepelin, Kowalevsky (1873), Dewitz (1875), Huxley (1877), Cholodkowsky, Bugnion (1891), and Wheeler (1892). As shpwn, then, by our observations and those of Dewitz (Figs. 189 and 192), the rudiments of the ovipositor consist of three pairs of tubercles, arising, as Kraepelin and also Bugnion (Fig. 191) have shown, from three pairs of imaginal discs, situated respectively on the seventh, eighth, and ninth uromeres, or at least on the three penultimate segments of the abdomen. With the growth of the 172 TEXT-BOOK OF ENTOMOLOGY semipupa, the end of the abdomen decreases in size, and is gradually incurved toward the base (Fig. 193), and the three pairs of append- ages approach each other so closely that the two outer ones com- pletely ensheath the inner pair, until a complete extensible tube is formed, which, by the changes in form of the muscles within, is gradually withdrawn entirely within the body. An excellent account of the honey-bee's sting is given by Cheshire (Figs. 194, 195). The outermost of the three pairs of stylets forming the apparatus is the A two thick, hairy "palpi" or feelers (P), these being freer from the sting proper than in the ovipositor of Orthoptera. The sting itself is composed of the two inner pairs of stylets ; one of these pairs is united to form the sheath (sA), •while the other pair form the two barbed darts. The sheath has three uses : first, to open the wound ; second, to act as an intermediate conduit for the poison ; and third, to hold in accurate position the long barbed darts. The sheath does not enclose the darts as a scabbard, but is cleft down the side presented in Fig. 194, which is below when the sting points backward. But, says Cheshire, as the darts move up and down, they would immediately slip from their position, unless prevented by a mechanical device, ex- hibited by B and (7, giving in cross-section sheath and darts near the end, and at FIG. 101. — A, end of larva of Encyrtns of 2d stage, show- ing the three pairs of imagiiiul buds of the ovipositor ijl, q", ij3. B, the same in an older larva ready to transform ; i, intestine ; a-, genital gland ; a, anus. — After Bugnion. the middle of the former. " The darts (d) are each grooved through their entire length, while upon the sheath (s/i) are fixed two guide rails, each like a prolonged dovetail, which, fitted into the groove, permits of no other movement than that directly up and down." The darts are terminated by ten barbs of .ugly form (Z>, Fig. 194), and much larger than those of the sheath, and as soon as the latter has established a hold, first one dart and then the other is driven forward by successive blows. These in turn are followed by the sheath, when the darts again more deeply plunge, until the murderous little tool is buried to the hilt. But these movements are the result of a muscular apparatus yet to be examined, and which has been dissected away to bring the rigid pieces into view. The dovetail guides of the sheath are continued far above its bulbous portion, as we DEVELOPMENT OF THE BEE'S STING 173 Fifi. 192. — Base of the ovipositor of Locustd rii'iiUxniiiia seen from beneath : c', sheath, or outer and lower pair of stylets turned to one side to show the others ; />', upper and inner pair ; b", third or innermost, smallest pair of stylets. A, the same on one side, in section. The shaded parts show the muscular attachments. The muscles which extend the apparatus and are attached to v , S, and ij, as also the membranes which unite the pieces from »j to y with each other and the body, are removed, so that only the chitinous parts remain. — After Dewitz. D FIG. 193. — Development of the sting in Bombus : A, a, 1st pair on Sth sternite ; b, 2d inner pair forming the darts ; c. outer pair. B-E, more advanced stages. F, a1, y, e, three pairs of tubercles, the germs of the male organs. 174 TEXT-BOOK OF ENTOMOLOGY see by E, Fig. 195 ; and along with these the darts are also prolonged upward, still held to the guides by the grooved arrangement before explained ; but both guides and darts, in the upper part of their length, curve from each other some- what like the arms of a Y, to the points c, c' (A, Fig. 194), where the darts Kic. 194. — Stinj; of bee x Ho times: A, sting- separated from Its muscles ; JIH, poison sac ; jiy. poison jfkind ; 'illi (/, ."'tli abdominal iraii^rlinn : n , H , nerves; c, external thin membrane joining stiiifr to last iihdoininul segment ; /'. /, /. :in. end of a dart, x 'Jin i : <>, <;. opi-iiiiif,'s for poison to escape into the wound. — After Cheshire. THE STRUCTURE OF THE BEE'S STING 175 make attachment to two levers (?, *'). The levers (k, I and k', Z') are provided with broad muscles, which terminate by attachment to the lower segments of the abdomen. These, by contraction, revolve the levers aforesaid round the points /, /, so that, without relative movement of rod and groove, the points FIG. 195. — Details of sting of bee : E, darts, sheath, and valves ; pb, poison-bap duct ; fo, fork ; .9, slide piece ; ra, valve ; b, barbs. f\ terminal abdominal segments ; ir, worker's sting ; tj, queen's stinir : /'. r', anal plate: £, sting1 entering skin: ,s/(, >heatli : . c. po.-itions in first, second, and third thrusts with the sting. //, portion of poison gland, x 3nn ; ,-n. cell nucleus; », nerve; g, sranirlionic cell. 7, portion of the poison gland, cells removed ; cd, central duct ; d, individual small ducts: jir. tunica propria. A", gland of Fni-nti,-n niftt : eft. central duct; <7, small ducts; KC, secreting1 cells. L, valve and support; t, trachea; T)>o<1« as we may call them, of Ephemeridae (Fig. 197), Neuroptera (Corydalus [Fig. 198], Myrmeleon, Ehaphidia), Trichop- THE STYLES AND GENITAL CLASPERS 177 tera, Lepidoptera, Diptera, and certain phytophagous Hymenoptera. They do not appear to occur in insects which are provided with an ovipositor. In Thysanura the A styles are present on segments 1-9 (Fig. 179). Those of the male Ephemeridae, of which there are two pairs arising from the ninth segment, are remark- able, since they are jointed, and they serve to represent or may be the homologues of two of the pairs of stylets composing the ovipositor of insects of other orders. The lower pair (Fig. 197, rh) are either 2-, 3-, or 4-jointed (in Oniscigaster 5- jointed), while those of the upper pair are 2-jointed (rh'). These rhabdopods in the ephem- erids are evidently very prim- itive structures, since they approach nearest in shape and in being jointed to the abdom- inal legs of Scolopendrella and the Myriopoda. The styles of the Orthoptera are survivals of the embryonic appendages of F[G 197 _ AMomen of Ellhemera (Lcpto. the ninth seo-niPllt fWheelpr pblebia) cupida, $: c, base of cercopoda; rh, -^ outer 8-jointed daspers or rhabdopods ; rh' , inner etc.). In Mantis they are seen i'air- A> side view- to have the same relations as the cerci, as shown by Heymons (Fig. 200). In the Phasmidoi, in Anabrus, and in the Odonata the cercopods, which are not jointed, are converted into claspers, and in the Odonata the claspers are spiny within, so as to give a firmer hold. The suranal plate is apparently so modified as to aid in grasping the female. In nearly all the Trichoptera there are, besides the suranal plate, which is sometimes forked FIG. 198. — End of abdomen of (Nosopus), a pair of superior and of Corydalus cornutus, rf : rh. rhabdo- • £ -, • pod ; c, cercopod. interior claspers, and in certain genera 178 TEXT-BOOK OF ENTOMOLOGY VIII (Ascalapliomerus, Macronema, Rhyacophila, Hydropsyche, Amphi- psyche, Sniicridea, and Ganonema) the lower pair are 2-jointed like those of Ephemeridse. The number of abdominal segments in the adult Trichoptera is nine, and McLachlau states that the genital armature consists of three pairs of appendages, i.e. a superior, inferior, and intermediate pair, besides the suranal plate (vestige of a tenth seg- ment) and the penis. Judging by his figures, these three pairs of append- ages arise from the last or ninth uro- mere, and the upper pair seem to be the homologue of the cercopoda of ephemerids. It needs still to be FIG. 199. — End of abdomen of embryo ascertained whether the intermediate of Mantis : r, rhabdopod ; c, cercopod ; sp, suranal plate; st, stigma on 8th segment, pair is a separate set, or merely sub- — After Heymons. -, • • • i j divisions of the upper or lower, and whether one of the latter may not arise from the penultimate seg- ment, because we should not expect that the last segment should bear more than one pair of appendages, as we find to be the case in arthropods in general, and in the Neuroptera. from which the Trichoptera may have originated. In most larvae of the Trichoptera, especially the Rhyacophilidae and Hy dropsy chidae, the last abdominal segment bears a pair of 2-jointed legs (cerco- poda), ending in either one or two claws, which under various forms, sometimes forming long processes, persist in the pupa; and there appears to be a suranal plate, the vestige of the tenth uro- mere. In the pupa, judging by Klapalek's Fy(, 20(V _Enf1 of abllmnon of peri plan eta americana, figure Of LeptOCerUS rf. *i'l«- view: <-. cen-.,p..d : .< stilus; /,. penis; t titillator; ra-analis, as we have called it) (Fig. 88, 89, .0- The podical plates or paranal lobes. --Tn the cockroach and other insects, also in the nymphs of Odonata, the anus is bounded on each side by a more or less triangular plate, the two valves being LITERATURE OF THE ABDOMEN AND APPENDAGES 183 noticeable in lepidopterous larvae. They are the valmdce of Bur- meister, and podical plates of Huxley, who also regarded them as the tergites of an eleventh abdominal segment ; ! and the subanal laminae of Heymons. They are wanting in Ephemeridae. The infra-anal lobe. — Our attention was first called to this lobe or flap, while examining some geometrid larvae. It is a thick, conical, fleshy lobe, often ending in a hard, chitinous point, and situated di- rectly beneath the vent. Its use is evidently to aid in tossing the pellets of excrement away so as to prevent their contact with the body. The end may be sharp and hard or bear a bristle. Whether this lobe is the modified ventral plate of the ninth urite, we will not undertake at present to say. The egg-guide. --In the Acrydiidse the external opening of the ovi- duct is bounded on the ventral side by a movable, triangular, acute flap, the egg-guide (Fig. 88, B, eg). Whether this occurs in other orders needs to be ascertained. LITERATURE ON THE ABDOMEN AND ITS APPENDAGES a. General (including the cerci, stili, etc.) Cornelius, C. Beitrage zur naheren Kenntnis von Palingenia longicaitda. (Pro- gramm d. Real- u. Gewerbeschule zu Elberfeld, 1848, pp. 1-38, 4 Taf. ) Schiodte, J. G. Bemerkungen iiber Myrmecophilen. Ueber den Bau des hin- terleibes bei einigen Kafergattungen. (Gerraar's Zeits. f. Ent., 1844.) De metamorphosi Eleutheratorum observationes. (Naturhist. Tidsskr. i-xiii, 1801-1883.) Meinert, F. Anatomia Forficularum. Anatomisk undersogelse af de Danske Orentviste, i. (Naturhist. Tidsskr. 3 raekke, ii, 1863, pp. 427-482, 1 PI.) Om dobbelte Saedgange hos insecter. (Naturhist. Tidsskrift, 3 raekke, v, 1868.) Tullberg, Tycho. Sveriges Podurider. (Svenska Vetensk.-Akad. Handl., 1872, x, Nr. 10, 12 Pis.) Davis, H. Notes on the pygidia and cerci of insects. (Journ. R. Micr. Soc., 1879, ii.) Westhoff, F. Ueber den Bau des Hypopygiuuis der Gattung Tipula Meig. (Minister, 1882, pp. 1-62, 6 Taf.) Saunders, Edward. Further notes on the terminal segments of aculeate Hyme- noptera. (Trans. Entom. Soc. London, 1884, pp. 251-267, 1 PI.) Palmen, J. A. Ueber paarige Ausflihrungsgange der Geschlechtsorgane bei Insekten. (Helsingfors, 1884, 5 Taf.) Haase, E. Die Abdominalanhange der Insekten mit Beriicksichtigung der Myriopoden. (Morpholog. Jahrbuch, 1889, xv, pp. 331-435, 2 Taf.) Abdominalanhange bei Hexapoden. (Sitzungsber. d. Gesellsch. natur- forsch. Freunde, 1889, pp. 19-29.) 1 In my account of the anatomy of Mel, pigmented . e layer; hy, hypoder- and are usually situated at the outlet of a pore-canal, which connects with an underlying cell of the hypo- dermis (Fig. 212). They are, then, bristle or hair-like processes arising from the hypodermis. Where the hairs or setae are rubbed off, their site is indicated by a minute ring like a follicle in the of SETM, OR HAIRS, BRISTLES, ETC. 189 chitinous integument. The cuticular hair, says Leydig, is in its first condition the secretion of the cellular element of the skin, and a thread-like continuation of the cell-body may rise up through the pore-canal into the centre of the hair, remaining there permanently. While the setae are usually simple, they are often branched, plumose, or spinulose, as in larval Hemerobidae, Anthrenus, and Dermestes, the larvae of certain coccinellid beetles, notably Epi- lachlia, and of Cassida, the larvae of arctians, etc., and in bees (Anthophila, Megachile, Osmia, Colletes, Apis, etc.). The use of these spinulose, plumose, and twisted hairs in the bees is clearly shown by J. B. Smith, who states that as these insects walk over flowers, the pollen grains adhere to the vestiture, " and this also accounts for the fact, probably noticed by every observant fruit-grower, that bees frequently bury themselves completely in the blossoms, or roll over every part of them. Such insects are after pollen, not honey, and by so rolling about, the pollen grains are brought into contact with and adhere to the surface of the insect." The syrphid flies also pollenize flowers, the pollenizing of chrysan- themums being effected, as Smith states, by Eristalis tenax, and he adds that the body vestiture of the syrphids " is often composed of spurred and branched hairs." (For reference to gathering hairs, see p. 45.) Certain remarkable spines occur in limacodid larvae, notably Em- pretia and Adoneta. These we have called caltrops spines, from FIG. 213. — Cuticular spinnles of larva of Adoneta: a, b, c, d, different forms; e, e', caltrops. their resemblance to the caltrops formerly used in repelling the attacks of cavalry. They are largely concerned in producing the poisonous and irritating effects resulting from contact with the cater- pillars of these moths, and are situated in scattered groups near the end of the tubercles. A group of three is represented at Fig. 213, e. They are not firmly embedded in the cuticle, but on the contrary 190 TEXT-BOOK OF ENTOMOLOGY appear to become very easily loosened and detached, and they prob- ably, when brought into contact with the skin of any aggressor, burrow underneath, and are probably in part the cause of the con- tinual itching and annoyance occasioned by these creatures. It will be seen by reference to Fig. 213, e', that the body of the spine is spherical, with one large, elongated, conical spine arising from it, the spherical base being beset with a number of minute, somewhat obtuse spinules. Glandular hairs and spines. — In some insects occur fine, minute, hollow setae from which exude, perhaps through pore-canals of ex- a b a A FIG. 214. — Glandular hairs of caterpillars. A, Daxylophitt aiitjtiiini : a. of l>oily ; b, of head ; e, of prothoraeie shield. B, < ', /•'<(' : ); pglc, four poison cells ; p, the poison in the hollow of the spine. hypodermal cells situated under the base of the spine. In the venomous spines of Lagoa crispata the poisonous fluid in the larger spines (Figs. 215, C, 216, b) is secreted in several large cells situated at the base of the spine, and this is the usual form. In the finer spines of a large tubercle (Figs. 215, A, 216) there appears to be a differentiation of the hypodermal cells into two kinds, the large, basal deep-seated, setigenous cells (216, sc) and the poison-secreting nuclei (216, pylc) situated nearer the base of the setae. The spines being filled with poison and breaking into bits in the skin of the hands or neck, caxise great irritation and smarting. These nettling or poisonous hairs or spines are especially venomous in the larva of 192 TEXT-BOOK OF ENTOMOLOGY Orgyia, Empretia stimulea, Hyperchiria io, the larvae of the saturnians (Fig. 217) and lasiocampids, etc. They rarely occur in insects of other orders, though the skin of Tele- phorus is said by Leydig to bear glandular hairs. Leydig states that in the stout bristles of Saturnia there is, as in the integument of the body, a homogeneous cuticula, under which is the cellular matrix (hypodermis), and the clear contents (hyaloplasma) are secreted from the blood. The cell-structure of the hairs consist, as in the cells of the body, of spongioplasma and hyaloplasma. Leydig has observed the droplets of the secretion of the caterpillar of Saturnia carpini oozing through distinctly observ- able pores, and states that there are similar openings in the hairs and scales. Dewitz found easily observable openings at the end of the hair of a large exotic weevil (Fig. 130) . The advanced nymph of Psylla is also armed with clavate glandular hairs (Fig. 178). The tubercles are outgrowths of the body- walls ; they are either smooth, warty, or spiny, as in many caterpillars. While the armature of insects is of little morphological sc--- Fio. 216. — Section of a subdorsal tubercle from a larva in stage I : fte, the setigenous cells, one for each seta ; pglc, nuclei by which the poison is secreted ; «, seta ; p, poison in middle of a broken spine ; out, cuticle ; s ^ 7. i H p j ! i\ A' Hi * ' > r 1 rfl: « • a \ v \ 1 ' , IS ' I <; r 1 Fio. 221. — Flattened and spinulated hairs of tufts of larva of Acronyota hastulifera. acteristic of the Lepidoptera, not a species of this great order being known to be entirely destitute of them. The scales vary much in shape, but are more or less tile-like, attached to the surface of the body or wing by a short slender pedicel, and are more loosely connected with the in- tegument than the hairs, •which are thicker at the base or insertion than beyond. The markings of the scales, both of Synaptera and Lepidoptera, are very elaborate, consist- ing of raised lines, ridges, or striae with transverse ridges between. " The striae of the transparent scales of Micropteryx are from about 500 to 300 to the millimetre, varying in different species. The Fio. 222. — Scales from dorsal tuft on second thoracic segment of larva of Qastropaeha querc/'J/i/in. 'USE OF THE SCALES 195 opaque scales of Morpho, which show metallic reflections, have about 1400 striae to the millimetre." (Kellogg.) The primary use of scales, as observed by Kellogg, is to protect the body, as seen in. Synaptera and Lepidoptera. A nearly as important use is the production of colors and patterns of colors and markings, while in certain butterflies certain scales function as the external openings of dermal scent-glands, and they afford in some case's (as first claimed by Kettelhoit in I860) generic and specific characters. Spuler has shown that the scales are strengthened by internal chitinous pillars. Burgess has observed in the scales of Danais plexippus that the under surface of the scales is usually smooth, or provided with few and poorly developed ridges, and this has been confirmed by Spuler and by Mayer (Fig. 226). In the irised and metallic scales the ridges, says Spuler, are not divided into teeth, and they converge at the base to the pedicel and also toward the end of the scale (Micropteryx), or end in a single process beyond the middle (the brass-colored scales of Phisia chrysitis). The arrangement of the scales on the wings is, in the generalized moths, irregular ; in the more specialized forms they are arranged in bands forming groups, and in the most specialized Lepidoptera they are more thickly crowded, overlapping each other and inserted in regular rows crossing the wings, these rows either uniting with each other or running parallel. (Spuler.) The scattered irregular arrangement seen in Micropteryx is also characteristic of the Tri- choptera and of Amphientomum. Development of the scales. - - The mode of origin of the scales was first worked out by Semper in 1886, who stated that in the wing of the pupal Sphinx and Saturnia they are seen, in sections, to arise prc. Fi«. 223. — Portion of a longitudinal section throiii,rh Mm- of thf younir pupal wings of a sum- mer pupa of I'niit'tstHt (Hif/njiii : s, young scale; leu. c//., leucocyte : iiil>i . jir., ground membrane ; J>rc, liyitoclermis-cells. brpr FIG. 224. — Portion of a longitudinal section through one wall only of the pupal wing of a specimen slightly older than that of Fig. 2'2M ; .v, older scale. from large roundish cells just under the hypodermis and which have a projection which passes out between the hypodermis (his " epidermis ") cells, expanding into a more or less spherical vesicle, the latter being the first indication of the future scale. He 196 TEXT-BOOK OF ENTOMOLOGY observed that the scales are not all formed at once, but arise one after another, so that on one and the same wing the scales are in different stages of development. More recently Schaeffer has stated that the scales and also the hairs are evaginations of greatly enlarged hypodermis cells, and still more complete evidence has been afforded by A. G. Mayer (1896). In the wings of Lepidoptera, about three weeks before the imago emerges, certain of the hypodermis cells, which occur at regular inter- vals, begin to increase in size and to project slightly above the level of the hypodermis ; these are Semper's " formative cells," and are des- tined to secrete the scales. They increase in length, and appear as in Fig. 223. In the next stage observed, the projections are much longer (Fig. 224). The hypodermis is now thrown up into a regular series of ridges, which run across the wing. Each ridge, says Mayer, corresponds in position with a row of formative cells, and each furrow with the interval between two ad- jacent rows. The scales always project from the tops of these ridges. The ground or basal mem- brane has not participated in this folding, and the deep processes of the hypodermis (p?r) that once extended to this membrane have largely disappeared. Figure 225 represents a more advanced stage almost eight days before the emer- gence of the imago. The scales are originally filled with protoplasm, which gradually withdraws, leaving behind it little chitinous bars or pillars which serve to bind together the upper and lower surfaces of the scales, and finally the scales become " merely little flattened hollow sacs containing only air." As Mayer shows (Figs. 226, 227), from the study of scales examined four days before emergence of the butterfly (Danais), "the striations upon the upper surface of the scale are due to a series of parallel longitudinal ridges," while the under side is usually smooth. The mode of insertion is seen in Fig. 227. The narrow cylindri- cal pedicel of the scale is merely, according to Semper, inserted into a minute close-fitting socket, which perforates the wing-membrane, Fio. 225. — Portion of a longitudinal section through a pupal wing about. eight days before emergence : xy formative scale-cell ; upper «, a scale. SPINULES AND HAIR-SCALES 197 and not into a tube, as Landois supposed. Spuler describes a sort of double sac structure or follicle (Schuppenbalg) which receives the hollow pedicel of the scale. This was originally (1860) observed by F. J. Carl Mayer, but more fully examined by Spuler (Fig. 228) though not detected by A. G. Mayer. Spinules, hair-scales, hair-fields, and androconia. — Besides the scales, tine spinules occur on the thickened veins of the wings of eual FIG. 226. — Portion of a cross-section through the pupal wing of D