Protection of Embryo

During the early stages of development, embryos are equipped with specialized structures that safeguard them against physical harm. These protective structures exist in all embryos, whether they are developing inside or outside the body.

 

Embryonic Protection

Protective coatings, in the form of membranes or coats, serve as specialized structures to shield the embryo. An excellent example of these protective structures can be observed in the developing chick embryo.

 

Protection through Internal Development

In most mammals, development occurs within the reproductive tract or uterus, providing a secure and moist environment for the embryo's growth.

Duckbill Platypus

Lower Vertebrates

In some lower vertebrates, such as sharks and reptiles, embryos develop in the uterus, where there is no biological connection between the mother's tissue and the embryo. The uterus only provides a secure environment for the embryo, while the nutrition necessary for the developing embryo is supplied by the egg.

 

Mammals

Mammals are divided into three subcategories: Prototheria, Metatheria, and Eutheria.

 

Prototheria

Prototheria, or egg-laying mammals such as the Duckbill platypus, produce eggs similar to those of reptiles. The eggs are retained in the female's body for some time before being laid in a nest and hatched. After hatching, the mammary glands of the mother produce milk, which feeds the neonates or newborns, a critical step in caring for the young.

 

Opossum

Metatheria

Metatheria, also known as pouched mammals, such as the Opossum and Kangaroos, have small eggs with limited yolk. Early development occurs within the female's body, and then the immature infants emerge from the mother's body. They crawl up the female's belly and enter the pouch, where they are sheltered and kept warm. Mammary glands inside the pouch feed each infant as it continues to grow and develop. The young remain in the pouch until they are old enough to survive independently.

 

Eutheria

Eutheria, or placental mammals, such as cows, goats, and humans, develop a structure called the placenta between the developing embryo and the female's uterus. The placenta is responsible for exchanging nutrition and waste materials between the mother and the embryo. Eggs contain a minimal amount of yolk, so the female provides the essential food components to the embryo via the placenta. After birth, the newborns are fed with milk secreted by the mammary glands. Placental mammals, therefore, provide optimal nutrition and protection to the developing embryo.