Internal and External Fertilization

There are two mechanisms by which fertilization can take place. 
Internal Fertilization - In some animals  like humans and birds , the sperm fertilize the egg inside the female's body. This is called internal fertilization. Both male and female get close together so that the male can inject the sperm into the females body. This is called mating.

External Fertilization - In other animals , the male deposits the sperm on the eggs outside the body of the female. This is called external fertilization. For some fish and frogs , fertilization is external.

snails eggs