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Oviparous and Viviparous Animals

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Oviparous and Viviparous Animals - Lesson Summary

Based on the production of young ones, animals can be oviparous or viviparous animals.

       •  Oviparous animals are the animals which lay eggs. e.g. Hen, Frog, Fish.
       •  Viviparous animals are the animals which give birth to the youngones. e.g. Human being, Cat, Tiger.

Most of the oviparous animals undergo external fertilisation, while viviparous animals undergo internal fertilisation.
       •  External fertilisation is the process which involves the union of male and female gametes outside the body.
       •  Internal fertilisation is the process which involves the union of male and female gametes  takes place inside the body.

EXTERNAL FERTILISATION   INTERNAL FERTILISATION   Fertilisation process occurs in the outside environment.  Fertilisation occurs inside the female body.  Organisms of opposite sexes release their gametes into the same medium such as water.  Male discharges male gametes into the female body during copulation.  Development occurs completely in the outside environment. ·        Development takes place in the female body during gestation period. Fishes, frogs exhibit external fertilisation. Human beings, cow, birds exhibit internal fertilisation. 

Reproduction in oviparous animals
Development in insects
Fertilisation in insects is internal. Mother lays fertilised eggs on a leaf or any other support. Eggs develop into larva. Larvae are also called as caterpillars. Caterpillars undergo moulting to form a pupa. Pupa undergoes moulting to transform itself into an adult.

Development in chick
       •  Hen is said to be oviparous as it lays the egg.  But the fertilisation is internal.
       •  After fertilisation, the zygote undergoes rapid division and moves down the oviduct.
       •  As it travels down the oviduct, many protective layers form as a hard shell around the developing embryo.
       •  Egg contains only the embryo when laid by the hen. Embryo is not fully developed. Hen sits on the egg to provide warmth necessary for the development of chick. All the developmental stages are completed within the egg. 
       •  The chick hatches from the egg after three weeks. Young chick hatching out of the shell is  has all the body part though they are immature.

Development in frog
During rainy season as female frog lays eggs entangled in jelly like substance on the surface of water. This mass of eggs surrounded by jelly is called as spawn. Immediately, male frog deposits sperms over the eggs. Sperms swim with the help of their tail and randomly fertilise the eggs. 

There are three distinct stages in the life cycle of a frog - egg, tadpole and adult.
       •  During external fertilisation, the egg fuses with a sperm to form a zygote.
       •  The zygote further divides to form an early tadpole, which matures into a late tadpole. Tadpole is totally different from that of an adult. Tadpole has a tail which is later lost in the adult. Tadpole uses gills for respiration. Slowly gills are replaced by lungs when these tadpoles grow and come out on to the land.
       •  During metamorphosis, the tadpole transforms into an adult frog. Metamorphosis is the process which involves drastic changes transforming larva into an adult.
       •  Adult frog can live both on land and in water. Frogs are cold blooded animals which can respire through skin, gills and lungs at different stages of their life cycle.

Reproduction in viviparous animals
Development in humans
Human male ejaculates semen with sperms into female reproductive tract during the process of copulation.
       •  Sperms swim up to meet the ovum.
       •  Fertilisation is internal and takes place in the fallopian tubes. Zygote is formed as a result of fertilisation.
       •  Zygote undergoes cleavage by forming 2,4,8,16,32 celled stages. These cells differentiate themselves into organs forming an embryo.
       •  Embryo comes down and gets implanted in the wall of uterus. There is a connection established between embryo and the uterus which is called as placenta.
       •  As the embryo becomes 5- weeks old, it has rudimentary eyes and a beating heart.
       •  As the embryo becomes 12-weeks old, the embryo is almost developed and is now called as foetus. Gestation period in human beings is about 9 months.
       •  A fully developed foetus is delivered from the mother by the process of parturition.
       •  Human beings give birth to fully developed youngones.
       •  Almost all the organs are formed in human beings at the time of birth itself. Metamorphosis is not observed in human beings.
       •  As human beings grow, body undergoes certain changes during transformation from childhood to adolescent stage.



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