Discuss internal and external methods of fertilization

Sexual reproduction starts with the combination of a sperm and an egg in a process called fertilization. This can occur either outside the bodies or inside the female. Both methods have advantages and disadvantages. Once fertilized, the eggs can develop inside the female or outside. If the egg develops outside the body, it usually has a protective covering over it. Animal anatomy evolved various ways to fertilize, hold, or expel the egg. The method of fertilization varies among animals. Some species release the egg and sperm into the environment, some species retain the egg and receive the sperm into the female body and then expel the developing embryo covered with shell, while still other species retain the developing offspring through the gestation period.

What You’ll Learn to Do

• Define the term fertilization
• Discuss external methods of fertilization
• Discuss internal methods of fertilization
• Describe the anatomical adaptations that occurred in animals to facilitate reproduction

Learning Activities

The learning activities for this section include the following:

• Fertilization
• External and Internal Fertilization
• The Evolution of Reproduction
• Self Check: Fertilization