Comparative Anatomy Early Embryology Kardong Chapter 5 Part 7

Vertebrate Egg Amniotic egg- amnion present Figure 7.1. Cledoic egg. Amniotic egg- amnion present Reptilian egg- possesses shell(cleidoic)

Egg Type Microlecithal egg- small amount of yolk Mammals Mesolecithal egg- moderate amount of yolk Amphibians Macrolecithal egg- large amounts of yolk Reptiles, birds, sharks

Types of Cleavage Holoblastic- division into two equal sized cells (e.g., in mammals) Meroblastic- restricted to periphery, usually in embryos with large amounts of yolk. Meroblastic discoidal - Blastodiscs occur in some fishes, reptiles, birds, and monotremes Figure 7.2. Blastodisc.

Amphibian Embryogenesis Figure 7.3. Frog development; stages of embryogenesis (book fig. 5-12)

Initial: fertilized egg with fertilization membrane (arrows) Cleavage Stages Figure 7.4. Initial: fertilized egg with fertilization membrane (arrows) 2 cell stage; 1st cleavage 4 cell stage; 4 blastomeres 8 cell stage; micromeres and macromeres 16 cell stage (not shown) 32 cell stage; morula 64 cell stage; blastula with blastocoel cavity

Cleavage Stages (cont’d.) Figure 7.5. Cells push inward to form gastrula Eventually eliminates blastocoel

Gastrulation Archenteron- primitive gut Blastopore Figure 7.6. Gastrulation. Archenteron- primitive gut Blastopore Gives rise to anus in deuterostomes Gives rise to mouth in protostomes 3 primary germ layers Figure 7.7. Cross section of frog gastrula.

Dorsal lip - invagination of cells Move around yolk cells Yolk plug Figure 7.8. Early frog gastrula. Dorsal lip - invagination of cells Move around yolk cells Yolk plug Notochord forms from mesodermal cells

Neurulation Neural plate thickens and pushed inward Neurectoderm- gives rise to nerve tube Neural crest cells- between nerve tube and ectoderm Dorsal root ganglion, branchial cartilages cells, and pigment cells Anterior cells- dermis of face, cephalic armor, sensory capsules Figure 7.9. Embryonic neurulation.

Figure 7.10. Neural crest cell differentiation. (Table 5.2; page 189).

Dorsal Mesoderm Dermatome- associated with ectoderm Myotome Figure 7.11. Dermatome- associated with ectoderm Dermis in most of body Myotome Skeletal muscle Sclerotone- associated with nerve tube Skeletal and vertebral column

Dorsal mesoderm (somite) splits to form coelom cavity Somatic mesoderm - bound to ectoderm Splanchnic mesoderm- bound to endoderm Somatopleure - somatic mesoderm meets ectoderm Splanchnopleure - splanchnic mesoderm meets ectoderm Figure 7.12. Mesoderm specialization (book Fig. 5.6).

Dorsal Mesoderm Differentiation Figure 7.13. Dorsal mesoderm (somite)- Epimeric mesoderm Intermediate mesoderm- Mesomeric mesoderm Lateral plate mesoderm- Hypomeric mesoderm

Primary Germ Layers Figure 7.14. Formation of the three primary germ layers.

Germ Layers (cont’d.) Figure 7.15. Organs derived from the germ layers.

Structures formed from the three germ layers. Figure 7.16.

Ectodermal placodes in a representative vertebrate. Figure 7.17.

Extraembryonic Membranes Figure 7.18. Extraembryonic membranes of cledoic egg.

Extraembryonic Membrane Formation in a Bird Figure 7.19. Extraembryonic membranes.

Principles of Embryology Figure 7.20. Embryological development.