32.1    The Natural History of Amphibians

	Most amphibians start life as aquatic larvae but live their adult lives on land.
	Amphibians were the first vertebrates to live on land.
	The strong bones, girdles and muscles of amphibian limbs enable them to support their bodies and move on land.
	Fossil evidence points to be lobe-finned fish as the ancestor of modern amphibians.
	The Devonian period was a time of mild temperatures and alternating floods and droughts.
	Amphibians evolved in the late Carboniferous period.
	Insects provided a source of food for amphibians.
	On land, amphibians had little competition for food and there was no predators.
	Urodels retain their tails throughout life.
	Salamanders are brightly colored with stripes and spots.

32.2    Structure and Function in Amphibians

	Many amphibians breathe through gills as larvae but breathe through lungs as adults.
	The bumps or "warts" on the skin of a toad are actually poison glands under the skin.
	Alkloids - toxic chemicals in frog and toad's skin.
	Liver - organ that produces bile.
	Pancreas - secretes enzymes into small intestine that breaks down food.
	The double-loop circulatory system with a three-chambered heart helped distribute oxygen to cells and remove wastes and CO2.
	This arrangement allows more oxygen-rich blood to circulate than a two-chambered heart.
	Kidneys regulate the amount of water in the body according to the amphibians environment.
	Nictitating membranes keeps the eye moist in air and protects it in water.
	Tympanic membrane are capable of receiving sound waves.
	Male frogs have special pouches in the throat that amplify the calls.
	Salamanders have strong homing instincts.
	Salamanders respond to the Earth's magnetic field and polarized light from the sun.

32.3    Reproduction and Development

	Jellylike coating on eggs protect them from injury, disease and temperature.
	It also provides nourishment for developing embryos.
	Females of poison-arrow frogs lay eggs in moist places on land.
	Tadpoles get on parent's back to be carried to water for further development.
	Thyroxine - hormone that triggers metamorphosis.
	Neoteny - reproductive adults retain larval characteristics.

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