Difference between internal fertilisation and external fertilisation are

The process of transformation of larva into an adult through drastic changes is called metamorphosis, e.g. development of caterpillar or pupa into silkworm and development of tadpole into frog.

Embryo gets embedded in the uterus of female for further development.

The mode of reproduction in which a single organism is able to produce one or more individuals of its kind is called asexual reproduction. It does not require both male and female parent.
The two methods of asexual reproduction in animals are given below:
(i) Budding It is the mode of asexual reproduction in which small bulges called buds develop and get separated from parent to form new individuals, e.g. in Hydra.
(ii) Binary fission It is the division of nucleus into two nuclei followed by the division of cytoplasm body. Each part receiving a nuclei and develops into two new individuals, e.g. in Amoeba.

The process of development of tadpole into an adult frog is known as metamorphosis.

Yes, there are organisms that have both male and female reproductive organs in the same body, e.g. earthworm, leech.

Reproduction is the biological process of formation of young ones of their own kind by living organisms.

Hydra (multicellular) and Amoeba (unicellular) are two animals which can reproduce by asexual methods.

In human beings, male gamete is known as sperm and female gamete as egg or ova.

A fertilised egg is also called zygote.

Hens lay eggs after fertilisation, therefore their eggs are covered with hard shell to protect the young ones. This shows that fertilisation in hen is internal. The frogs on the other hand lay both sperms and eggs in water prior to fertilisation. Thus, the fertilisation in frog takes place in water, hence it is external.

Female fish lay eggs in water while male fish release their sperms in water. Sperms swim and reach the eggs of fish, randomly due to water currents.
When a sperm comes in contact with the viable egg, nuclei of both the cell fuses to form a zygote. This process of fertilisation takes place in water outside the female body, hence fertilisation is external in fishes.