what is the e.g. of tertiary egg membrane ?
Answers
Answer:
The tertiary membranes are secreted by cells of the female’s genital tract when the ovum moves through the oviduct.
Tertiary membranes include the gelatinous membranes of the eggs of echinoderms, mollusks, fish, and amphibians.
They also include the tough protein membranes that are clad in the horny shells of cephalopods and selachians, the fibrous and calcareous shells of reptiles, and the undershell membranes and the calcareous shells of birds.
In many invertebrates a tough tertiary shell, called a cocoon, surrounds several eggs. The cocoon contains protein fluid, which serves as a fluid tertiary membrane.
If the tough membranes form before the egg cell and the spermatozoon unite, special canals known as micropyles form. The micropyles enable the spermatozoon to reach the cytoplasm of the ovum without obstruction.
On the basis of origin, egg- membranes are divided into three parts
(1) Primary egg membrane: Oocyte secretes this membrane Examples: Zona Pellucida, Vitelline membrane etc.
(2) Secondary egg membrane: This is seen outside the primary egg membrane & is secreted by the ovary. Examples: Chorion, corona radiata
(3) Tertiary egg membrane: This is present outside the primarveca membrane
uterus or the oviduct. Examples: Jelly coat, Shell & Shell membrane.
Some functions of Egg-membranes are as follows:
1. To provide protection
2. To prevents the egg from dessiciation.
3. To provide buovence to the ambian exis
4. To check polyspermy.