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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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