­American Football is played by two opposing teams of eleven. The football field measures 91.4m by 48.8m and is markedoff by latitudinal stripes every 4.57m. At either end there is and end-zone which measures 9.14m across. In the center of each end-zone stand g­oal posts 6.1m high, with a crossbar ­3.05m above the ground and with the uprights on either end 7.2m apart. The object of the game is to move the ball across the opponent's goal line, thereby scoring a touchdown, worth six points.

Amphibians (class Amphibia, from Amphi- meaning "on both sides" and -bios meaning "life"), such as frogs, toads, salamanders, newts, and caecilians, are ectothermic (or cold-blooded) animals that metamorphose from a juvenile water-breathing form, either to an adult air-breathing form, or to a paedomorph that retains some juvenile characteristics. Proteidae (mudpuppies and waterdogs) are good examples of paedomorphic species.