Epigenesis

Wolff proposed this theory.His explanations are based on the observation of the development of chick embryos.it is an antithesis of preformation this theory.states that there is no preformed embryo inside the egg.The egg is formed of only granular substances.These granules during development are arranged to form cellular layers called germinal layers.these layers grow thick in some parts ,grow thin in some other parts and turn into pockets in other parts and at last become the body of an embryo.

Preformation Theory

Preformation theory is an ancient theory giving an interesting  explanation of the development of an organism.It was proposed by Malpighi.According to this theory the Ovum or gametes  contain in them a mini preformed embryo.Malpighi stated that the ovum contains a miniature adult animal called homunculus.During development the homunculus expands and increases in size

Leeuwenhock in 1677 believed that the preformed embryo is inside the sperm.These scientists are called animalculists


  In parthenogenesis the egg develops into an animal without the assistance of spermatozoon.If the egg can develop with out fertilization .The embryo can not be preformed inside the spermatozoon.Anyhow this theory is not at all accepted.

Note: Animalcule is the old name of sperm.
There  are two groups of scientist Animalculists and Ovists.

Fluid Theory

The Greek philosopher ,Empedoes thought that each parent produces a fluid known as semen which arises contiguously from the various parts of the body and is  responsible for the production of an embryo in the uterus of the female.

Aristotle the Greek philosopher (384-322 BC)was of the opinion that the child was produced  by the mixing of semen of man and menstrual fluid during sexual intercourse .He gazed man's semen as a highly purified form of his blood.He considered the woman's menstrual fluid as female semen.

Vapour Theory

The Greek philosopher Pythagoras ex cogitate that a moist vapor liberated from the body of the male is responsible for the development of an embryo in the uterus of the female.