Both Hydra and Amoeba reproduce asexually involving only single parent but the modes are different. Hydra reproduces from bulges or buds arising from the parent body that grows and matures into another organism, while Amoeba reproduces by binary fission.

Difference between viviparous and oviparous animals are

Sperm is a male reproductive cell. It is also called a male gamete. It is a single cell with all cell components. It is tiny with a head, a middle piece and a tail. The long tail helps to move through the female tract.

Difference between internal fertilisation and external fertilisation are

Reproduction is important for continuation of species, generations after generations. It also helps in production of new individuals of same kind and transmission of certain characters from parents to off springs.

(i) Examples of viviparous animals Mammals like cat, dog, camecow, dog.
(ii) Examples of oviparous animals All birds, fishes, reptiles, amphibians.

Organisms like honeybees, birds (turkey) and some lizards are reproduce by parthenogenesis.

Embryo grows outside in open in case of external fertilisation.

Two main types of reproduction prevalent in animals are asexual and sexual reproduction.

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

(a) Fertilisation is the term used for the fusion of a male gamete (sperm) and a female gamete (ovum or egg) to form a zygote during sexual reproduction.
(b) Internal fertilisation takes place in humans.
(c) Fertilisation mainly occurs in the Fallopian tube.

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.

The animals in which fertilisation occur in water, i.e. they lay eggs and release sperms outside body and thus the young one too is formed outside the body in water. Such aquatic animals are oviparous with external fertilisation.

Hen is the odd member among the list. Hen lays eggs outside its body, i.e. it is oviparous, while rest gives birth to young ones.