The skeletons of all vertebrate embryos are made up of cartilage but are usually replaced by bone as they grow
Warm-blooded animals warm their bodies by capturing the heat released by chemical reactions in their cells
Cold-blooded animals only live in cold places
Gills allow organisms to breathe in the water as well as on land
A flexible tissue that gives support and protection but is not rigid like bone
Animals that maintain a constant body temperature despite changes in the environment
The fertilization of eggs by sperm in side the female's body
Animals whose body temperatures change with the environment.
The fertilization of eggs by sperm outside of the female's body
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