Development Lab

1. Development Lab Biology 113

2. Yolk Distribution • Isolecithal • Telolecithal

3. Holoblastic versus Meroblastic cleavage • Holoblastic cleavage, the complete division of the egg occurs in species whose eggs have little or moderate amounts of yolk, such as sea urchins and frogs • Meroblastic cleavage, incomplete division of the egg occurs in species with yolk-rich eggs, such as reptiles and birds

4. Gastrulation

5. Neurulation

6. Sea Star Development • Identifiable stages are: • ovum, an unfertilized egg; nucleus and nucleolus are visible • zygote, a fertilized egg (diploid); the nucleus is not visible • 2 cells, the product of mitosis of the zygote, cells size is halved • 4 cells • 8 cells

7. Sea Star Development • Identifiable stages are: • morula (like a compact cluster of grapes) • blastula, a hollow ball of cells—early, middle, and late stages are determined by cell size, which gets smaller with each round of mitosis

8. Sea Star Development Gastrula in which the surface pushes into the interior at a point called the blastopore to form a tube that will become the digestive system. In a gastrula the cells on the outside are ectoderm, those lining the inner tube are endoderm, and cells that migrate and multiply between these layers will become the mesoderm.

9. Unincubated Chicken egg

11. 24 hr chick (neurulation)

12. 48-hr Chick

13. 56-hr Chick

14. 96-hr Chick

15. Fetal Membranes of the Chick