$A$ : Fertilin protein is present in the egg membrane.
$R$ : It helps in agglutination reaction

During the development, the point of entry of sperm in the eggs at fertilization

Mesoderm gives rise to all the structures except

The amnion of mammalian embryo is derived from

$A$ : All copulations do not lead to fertilisation and pregnancy.
$R$ : Fertilisation can occur if the ovum and sperms are transported simultaneously to the ampullary-isthmic junction