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Fertilization and Development. Gestation. Fertilization. Internal Fertilization Mammals, Birds, Reptiles Small # of offspring External Fertilization Fish, Amphibians Large #’s of offspring. Internal vs. External Development. Internal . External.
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Fertilization and Development Gestation
Fertilization • Internal Fertilization • Mammals, Birds, Reptiles • Small # of offspring • External Fertilization • Fish, Amphibians • Large #’s of offspring
Internal vs. External Development Internal External Offspring develop outside of the female’s body, usually in water Large # of offspring Offspring are not well protected Birds, reptiles, amphibians and fish • Offspring develop inside of the mother’s uterus • Small # of offspring • Offspring are protected during development • Mammals - mainly land dwelling but whales and dolphins are exceptions
Early Stages of Development • Zygote – fertilized egg • Morula – solid ball of cells • Blastula – larger hollow sphere of cells • Gastrula – infolding of the blastula forms layers
Layers of the Gastrula • Endoderm • Inner layer • Forms organs spinal cord and brain • Mesoderm • Middle layer • Forms muscles and bones • Ectoderm • Outer layer • Forms skin
Placenta • Delivers oxygen, water, sugar and nutrients to the fetus • Removes carbon dioxide, urea and other waste products produced by the fetus