Question

Why do most land animals require a more developed embryonic feeding mechanism than aquatic animals?

Answer 1

Answer. Land animals or terrestrial animals shows internal fertilisation whereas the aquatic animals show reproduction by spawning, in which gametes are released into the water and thereafter fertilisation takes place, thus aquatic animals show external fertilisation.

As the development of embryo or embrogenesis takes place inside the female organism in the terrestrial animals, that is why the embryonic feeding mechanism is more developed in them.

As the gametes undergoes internal fertilisation, it leads to the formation of zygote. Zygote then divides to form the embryo. This is known as embryogenesis. In humans, embryogenesis includes the:

• Cleavage
• Gastrulation
• Organogenesis

At the end of the cleavage phase i. e. In blastula the placental initials are formed and this structure becomes more developed in the gastrulation phase and completely developed in organogenesis.

Placenta is chrioallantoic in origin in humans. It is a connection between the fetus and the mother's uterine part.

Placenta is connected to fetus with the help of umbilical cord, which becomes long as the fetal growth increases. Placenta is important structure, because it helps in:

• Providing nutrition to growing embryo which later becomes fetus (in organogenesis) from the mother's blood.
• It helps in excretion.
• It helps in exhalation.
• It helps in digestion.
• It helps in transport of antibodies from the mother's blood to the fetus. Generally, it is IgG. Most important, placenta is endocrine in nature, releasing various hormones like:

1. human Chorionic Gonadotrophin
2. Chorionic thyrotrophin
3. Chorionic corticotrophin
4. Relaxin
5. Progestrone
6. Human placental lactogen

As parturition occurs, the umbilical cord attached to the infant's navel is tied and extra one is discarded and so as with placenta.