Chapter III: 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