PART II. EMBRYOLOGY OF INSECTS

_a._ The egg 515

Mode of deposition 518 Vitality of eggs 520 Appearance and structure of the ripe egg 520 The egg-shell and yolk-membrane 520 The micropyle 522 Internal structure of the egg 524

_b._ 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

_f._ Formation of the external form of the body 542

Origin of the body-segments 542 The procephalic lobes 544 Fore-intestine (stomodæum) and hind-intestine (proctodæum), labrum 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 Hymenoptera true limbs? 552 The tracheæ 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

_l._ 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