CBSE Class 8 Answered

Internal fertilisation

• Fertilisation that takes place inside the female body is called internal fertilisation.  
• During internal fertilisation, the male inserts its sperms into the body of female.
• The sperms then fertilise the egg within the female's body.
• Internal fertilisation is seen in many mammals like dogs, cats, cattle, cows, human beings as well as in birds like hens and also in reptiles.

External fertilisation

• Fertilization that takes place outside the body of female animal is called external fertilisation. 
• When the male and female come together in water, the female lays hundreds of eggs.
• The eggs are not covered by a shell and are very delicate. They are held together by a layer of jelly which provides protection to the eggs.
• The male releases its sperms in water. With the help of their long tails, they swim randomly in water and when they collide with the eggs, it results in fertilization.
• External fertilisation is seen in amphibians like toads and frogs as well as in other aquatic animals like echinoderms, star fish and other fishes.