Development and Growth

Where Do Embryos Develop? Growing offspring, or the embryo, may develop outside or inside of the parent’s body. The offspring of some animals develop inside an egg laid outside of the parent’s body. Most animals without backbones lay eggs. The eggs of land vertebrates such as reptiles and birds, that develop in an egg outside of the parent’s body are called amniotic eggs.

Amniotic Egg

Egg Retaining Animals In some animals, an embryo develops inside an egg that is kept within the parent’s body. The developing embryo gets all of its nutrients from the egg’s yoke. What are some egg-retaining mammals that you can think of?

Placental Mammals In placental mammals the embryo develops inside the mother’s body. What are some examples of placental mammals? Materials are exchanged between the embryo and the mother through an organ called the placenta.

Placental Mammals Blood carrying food and oxygen from the mother flows to the placenta and then the embryo. Blood carrying wastes and carbon dioxide from the embryo flows to the placenta and then to the mother. The mother’s blood does not mix with the embryo’s blood and the placental mammal develops inside the mother’s body until its body systems can function on their own.

Placental Mammals

How Do Young Animals Develop? Some animals look like small versions of adults. Other animals go through a process of metamorphosis, or major body changes, as they develop from young organisms into adult organisms. What are some examples of animals that undergo metamorphosis?

Crustaceans Most crustaceans such as lobsters begin their lives as tiny, swimming, larvae that do not resemble adults. Through metamorphosis, crustacean larvae develop into adults.

Insects Insects undergo complete or incomplete metamorphosis.

Complete Metamorphosis Complete metamorphosis had 4 stages: egg, larva, pupa, and adult. In the pupa stage the insect is enclosed in a protective covering and major changes in body structures are taking place. The pupa does not eat and moves very little.

Incomplete Metamorphosis Incomplete metamorphosis has no distinct larval stage and has 3 stages: egg, nymph, and adult. An egg hatches into a nymph which usually looks like an adult without wings. As the nymph grows it may shed it’s exoskeleton several times.

Amphibians Amphibians such as frogs begin their life cycles as fertilized eggs in water. The larva of a frog is called a tadpole. The frog undergoes metamorphosis to become an adult. Does a frog go through complete or incomplete metamorphosis?

How Do Animals Care For Their Young? Most amphibians and reptiles do not provide parental care, while most birds and mammals typically care for their offspring. Offspring that do not receive parental care must be able to care for themselves from their time of birth.

Parental Care Most bird species lay their eggs in nests that one or both parents build. Some species can move around and find food right after they hatch while others are helpless and must be fed by the parent. Most parent birds feed and protect their young until they are able to care for themselves.

Parental Care Most mammals are usually quite helpless for a long time after they are born. All young mammals are fed with milk from the mother’s body and one or both parents may continue caring for their offspring until the young animals are independent.