The ovum secretes a chemical substance called fertilization and the sperm secretes a protein called antifertilizin .
This fertilizin - antifertilizin interaction causes agglutination of egg and sperm .
The sperm generally comes in contact with ovum in the animal pole .
Ovulation in the human female occurs at secondary oocyte stage in which meiosis -I have been completed and first polar body has been released but second maturation is yet to complete .
Penetration of sperm is a chemical mechanism .
In this acrosome of sperm undergoes acrosomal reaction and releases certain sperm lysins which dissolve the egg envelopes locally and make the path for the penetration of sperm .
These sperm lysins contain a lysing enzyme hyaluronidase which dissolves the hyaluronic acid polymers in the intercellular spaces which holds the granulose cells of corona radiata together , corona penetrating enzyme and acrosin .
Then it dissolves the zona pellucida .
Only sperm nucleus and middle piece enter the ovum . The tail is lost .
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