Comparative account of placentation

 COMPARATIVE ACCOUNT OF PLACENTATION

        The placenta is concerned with viviparous animals where the embryos develop within the body of mother. Because the embryo is in contact with stored egg-yolk, there is developed a tissues is called the placenta. 

        This type of relationship with the mother tissues is met with some functional connection with the maternal tissue. This association of maternal tissues with foetal viviparous fishes and reptiles. Here generally yolk sac and chorion are involved.

The differences in placentae of various mammals arise due to :-

 (i) the structure and of the villi and 

(ii) the degree of contact between the maternal and foetal tissues.