After implantation, finger-like projections on the trophoblast are called $...A....$ which are surrounded by $...B..$ and maternal blood. Here $A$ and $B$ refers to
$A-chorion; B-foetal\; cell$
$A-chorionic\; villi; B- uterine\; tissue$
$A-uterine\; tissue; B-chorionic\; villi$
$A-foetal\; cell; B-chorion$
In eggs which have very thick and resistant membrane e.g., fishes and insects sperm penetrate through a special canal called
The blastopore develops into future
The longest gestation period is found in
A hatching egg of chick is covered by plaster of paris. It is harmful for
Which hormone is secreted only post pregnancy in women?