What are mammalian eggs?
Answers
Mammalian eggs have very less amount of yolk, that's why eggs are oligolecithal & isolecithal or microlecithal & homolecithal. 0.1 mm is the usually size of mammalian eggs.
These type of eggs has 2 egg-membranes:
(1) Zona pelucida: It is a transparent membrane like covering & is a primary membrane secreted by the ovum or oocyte.
(2) Corona radiata: It is a layer of follicular cells & these cells are attached to the surface of egg with hyaluronic acid. This is constituted as the secondary membrane, which is secreted by the ovary. These eggs do not have tertiary membrane.
Answer:
Mammalian eggs
In placental mammals, the egg itself is void of yolk, but develops an umbilical cord from structures that in reptiles would form the yolk sac. Receiving nutrients from the mother, the fetus completes the development while inside the uterus.