TABLE OF CONTENTS xih 



PAGE 



The vent (anus) . 319 



Histology of the digestive canal 320 



6. 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 csecal 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 larvae . . . 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 :}97 



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 cells . . . . . 420 



Leucocytes or phagocytes in connection with the pericardial 



cells , 421 



