Chapter II: Part I: Morphology and Physiology

PAGE 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,
arthromeres, etc.) 30

_d._ Mechanical origin of the limbs and of their jointed
structure 35

THE HEAD AND ITS APPENDAGES 42

_a._ 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

_b._ Appendages of the head 57

The antennæ 57
The mandibles 59
The first maxillæ 62
The second maxillæ 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 tegulæ 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 111
Climbing 116
The mode of swimming of insects 116

_d._ The wings and their structure 120

The veins 121
The squamæ 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

_f._ The primitive origin of the wings 137

The development and structure of the tracheæ and veins of
the wing 144

_g._ Mechanism of flight 148

Theory of insect flight 150
Graber’s views as to the mechanism of the wings, flight,
etc. 153

THE ABDOMEN AND ITS APPENDAGES 162

The median segment 163
The cercopoda 164
The ovipositor and sting 167
The styles and genital claspers (Rhabdopoda) 176
Velum penis 181
The suranal plate 181
The podical plates or paranal lobes 182
The infra-anal lobe 183
The egg-guide 183

THE ARMATURE OF INSECTS: SETÆ, HAIRS, SCALES, TUBERCLES, ETC. 187

The cuticula 187
Setæ 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
Musculature of a beetle 213
Minute structure of the muscles 215
Muscular power of insects 217

THE NERVOUS SYSTEM 222

_a._ The nervous system as a whole 222

_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 antennal or olfactory lobes (Deutocerebrum) 237
The œsophageal lobes (Tritocerebrum) 237

_c._ Histological elements of the brain 238

_d._ The visceral (sympathetic or stomatogastric) system 238

_e._ The supraspinal cord 240

_f._ 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
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
movements of animals 259
How far can insects see? 260
Relation of sight to the color of eyes 260
The color sense of insects 260

_b._ The organs of smell 264

Historical sketch of our knowledge of the organs of smell 264
Physiological experiments 268
Relation of insects to smelling substances before and
after the loss of their antennæ 269
Experiments on the use of the antennæ in seeking for food 270
Experiments testing the influence of the antennæ 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 282
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
Orthoptera and other insects 288
Antennal auditory hairs 292
Special sense-organs in the wings and halteres 293

_e._ The sounds of insects 293

THE DIGESTIVE CANAL AND ITS APPENDAGES 297

_a._ The digestive canal 302

The œsophagus 303
The crop or ingluvies 303
The “sucking stomach” or food-reservoir 305
The fore-stomach or proventriculus 306
The œsophageal valve 311
Proventricular valvule 313
The peritrophic membrane 313
The mid-intestine 314
Histology of the mid-intestine 316
The hind-intestine 316
Large intestine 316
The ileum 317
The gastro-ileal folds 317
The colon 317
The rectum 318
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 cæcal appendages 347

_d._ The excretory system (urinary or Malpighian tubes) 348

Primitive number of tubes 353

_e._ Poison-glands 357

_f._ 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
Fœtid 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 larvæ 377
Dorsal and lateral eversible metameric sacs in other larvæ 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 supraspinal 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 cells 420

Leucocytes or phagocytes in connection with the
pericardial cells 421

_c._ The œnocytes 423

_d._ The phosphorescent organs 424

Physiology of the phosphorescence 426

THE RESPIRATORY SYSTEM 430

_a._ The tracheæ 431

Distribution of the tracheæ 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 tænidia 444

_e._ Origin of the tracheæ and of the “spiral thread” 447

Internal, hair-like bodies 451

_f._ 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 larvæ 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 spermatozoön 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