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1. Life History And Embryogenesis From: Ching Preparedby: Geonyzl L Alviola

12. flat space between epiblast and hypoblast cell disk on surface of yolk, bilaminar meroblastic (incomplete): initial cleavages planes limited to animal pole, the region opposite the yolk) telolecithal reptiles small sphere sphere with layered wall holoblastic mesolecithal (moderate yolk) amphibians, lampreys, lungfish, paddlefish, sturgeon large, central sphere sphere with single layer wall holoblastic (or complete): initial cleavage planes extend through egg) isolecithal, oligolecithal or microlecithal (little yolk) Amphioxus, mammals blastula cavity blastula type of cleavage type of egg Group

26. Cleavage of Microlecithal Eggs This picture is of the unfertilized egg. It can be differentiated from the zygote by the presence of a large, conspicuous nucleus (large arrow) with obvious nucleolus (smaller arrow) and by the lack of a fertilization membrane. Next…..

27. This shows the zygote (fertilized cell). It is recognized by the presence of the fertilization membrane (arrows) surrounding it and the peripheral, fluid-filled perivitelline space. Next….

29. Cleavage of Mesolecithal Eggs

30. Cleavage of Megalecithal Eggs From this enlarged cross-sectional view of the chick blastula, some important anatomical details are visible and labelled: Ao = Area opaca Ap = Area pellucida 1 = Blastocoel 2 = Subgerminal spa

32. All blastulas have two main components--the blastoderm and blastocoel . The blastoderm is the sheet of cells on the outside of the blastula. The blastocoel is the cavity on the inside.