1. Animal Reproductive Organs
3.3 Animal Reproduction
Animal Reproductive Organs
Gonads are specialized organs that produce sperm or eggs.
Testes are male gonads that contain a network of coiled tubes in which sperm cells form.
Ovaries are female gonads that produce egg cells.

2. Internal Fertilization
3.3 Animal Reproduction
Internal Fertilization
Internal fertilization happens inside the body of an organism.
Internal fertilization ensures that an embryo is protected and nourished until it leaves the female’s body.
Examples
Earthworms, spiders, insects, reptiles, birds, and mammals

3. External Fertilization
3.3 Animal Reproduction
External Fertilization
External fertilization occurs in the environment, outside of an animal’s body.
Most animals that reproduce using external fertilization do not care for the eggs or young.
Examples
Jellyfishes, clams, sea urchins, sea stars, many fish species, and amphibians

4. External Embryo Development
3.3 Animal Reproduction
External Embryo Development
Animals whose embryos develop outside the mother are usually protected inside an egg.

5. 3.3 Animal Reproduction
Metamorphosis
A developmental process in which the form of the body changes as an animal grows from egg to adult

6. Incomplete Metamorphosis
In incomplete metamorphosis, insects look like miniature adults when they hatch.
There are three life stages of incomplete metamorphosis.
larva
nymph
adult
nymph stage
larvae
adult

7. Complete Metamorphosis
In complete metamorphosis, the insect changes form entirely.
Larva
Egg
Pupa
Adult
There are three life stages of incomplete metamorphosis.
egg
larva
pupa
adult

8. 3.3 Animal Reproduction
Internal Development
The embryos of some animals, including most mammals, develop inside the mother.
A tissue or organ transfers nourishment from the mother to the embryo.
Other embryos—some snakes, insects, and fishes—develop in an egg with a yolk inside the mother.

9. 3.3 Animal Reproduction
Gestation
Gestation is the length of time between fertilization and the birth of an animal.
Gestation varies by species and usually relates to the size of the animal at birth—smaller animals have shorter gestation.