Immunology | Immune system| Immunity

STRUCTURE OF OVUM

The egg of frog is spherical in shape and about 2mm in diameter.It is surrounded by three membranes viz.,outer jelly coat,middle vitelline membrane and inner plasma mambrane.
The jelly coat is formed of albumin and vitelline membrane is made up of mucopolysaccharide. The egg cytoplasm (ooplasm) has 2 regions.viz.,peripheral cortex and central endoplasm.

The cortex is granular .It shows presence of cortical granules and dark brown pigment granules.Cortical granules are arranged in a layer close to the plasma membrane. The endoplasm contains numerous plate like structures called as yolk platelets.
The egg shows well-marked polarity.On one side is the animal pole containing nucleus. The polar bodies also containing nucleus. The polar body also occupy region near animal pole whereas vegetal pole containing nucleus. The polar bodies also occupy region near animal pole whereas vegetal pole containing yolk granules the animal pole appears darker whereas vegetal pole is yellowish or whitish(lighter) in colour. As the egg contains large amount of yolk it is also called as megalecithal.
As the yolk platelets are highly concentrated at one end,polarity is distinct and hence the egg is called as Telolecithal egg.
The shell is absent.Hence the egg is non-cleidoic egg.