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 ........ 524 



6. Maturation or ripening of the egg 525 



c. Fertilization of the egg .......... 525 



d. Division and formation of the blastoderm ...... 526 



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 (stomodaeum) and hind-intestine (proctodseum), 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 tracheae 553 



h. Nervous system ........... 554 



Completion of the definite form of the body 555 



t. 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 



TO. Length of embryonic life 582 



n. The process of hatching 583 



The hatching spines * . . . . 585 



